Recuperative Potential of Cardiac Muscle following Relief of Pressure Overload Hypertrophy and Right Ventricular Failure in the Cat

Transcription

1 RECUPERATIVE POTENTIAL IN HYPERTROPHY AND FAILURE/Coulson et al. 41 trolyte balane, and aldosterone and ortisol seretion in normal man and in irrhosis with asites. J Clin Invest 44: , Aiken JW, Vane JR: Intrarenal prostaglandin release attenuates the renal vasoonstritor ativity of angiotensin. J Pharmaol Exp Ther 184: , Hoobler SW, Romero JC: Experimental hypertension; the role of renin in the blood pressure elevation. Exerpta Media International Congress Series No. 302, 1973, pp Romero JC, Strong CG, Torres VE, Ott C, Knox FG: Plasma prostaglandins, plasma renin ativity and blood pressure in normal and renal hypertensive rabbits treated with indomethain. In Abstrats of the Annual Meeting of the Amerian Soiety of Nephrology, 1973, p Romero JC, Strong CG, Ott CE, Walker R, Shryver S, Manahan D: The effet of indomethain on the renin-angiotensin system (abstr). Clin Res 23: 372A, Romero JC, Dunlap CL, Strong CG: The effet of indomethain and other anti-inflammatory drugs on the renin-angiotensin system. J Clin Invest 58: , 1976 Reuperative Potential of Cardia Musle following Relief of Pressure Overload Hypertrophy and Right Ventriular Failure in the Cat RICHARD L. COULSON, SHAHRIAR YAZDANFAR, EMIR RUBIO, ALFRED A. BOVE, GERALD M. LEMOLE, AND JAMES F. SPANN SUMMARY This study examined the reuperative potential of at hearts subjeted to experimental right ventriular pressure overload (for a 10- to 14-day period) whih provoked hypertrophy with and without ongestive heart failure. Five groups of ats were studied: normal ontrols; one group with 70% pulmonary artery onstrition whih produed right ventriular hypertrophy (); one group with an 87% onstrition whih also produed right ventriular hypertrophy but with ongestive heart failure (); and two groups whih had been similarly subjeted to pressure overload but whih had been allowed a reovery period of 30 days after relief of the pressure overload. Both the 70% and 87% pulmoni onstritions were assoiated with extensive right ventriular hypertrophy, depression of myoardial ontratile funtion, and severe redution of ardia norepinephrine stores (normal, 1.42 /xg/g:, 0.11 /ig/g;, 0.01 /ig/g) - After a 30-day period of relief from the pulmoni onstrition normal hemodynami funtion returned. In ats in whih had been MYOCARDIAL ontratile funtion and funtion of the ardia sympatheti system are impaired when ventriular hypertrophy and ongestive heart failure result from a pressure overload on the heart.'" 5 There is well established therapy to relieve the pressure overload; for example, systemi hypertension an be treated by pharmaologial means and aorti stenosis an be relieved by ardia surgery. However, relatively little is known of the potential for reovery of ontratile funtion and repletion of my- From the Setion of Cardiology and the Setion of Cardia and Thorai Surgery, Temple University Health Sienes Center, Philadelphia, Pennsylvania. Supported by the Southeastern Pennsylvania Heart Assoiation and by Grants 5T01-HL and 3R01-HL from the National Institutes of Health. This work was ompleted during the tenure of fellowships granted to Dr. Coulson by the Medial Researh Counil of Canada and the Canadian Heart Foundation. Dr. Bove is an Established Investigator, Amerian Heart Assoiation. Dr. Yazdanfar's present address is: Albert Einstein Medial Center, Northern Division, Philadelphia, Pennsylvania Reeived July 28, 1975; aepted for publiation August 26, relieved, right ventriular weight and ontratile funtion were normal but ateholamine depletion persisted. Cats with relieved showed depressed ontratile funtion and depleted myoardial norepinephrine, and the right ventriular weight did not return to normal. Cardia musle of all pressure-overloaded nonrelieved hearts showed depressed veloity of shortening and depressed ability to sustain load. Cats with alone regained normal musle shortening veloity and load-bearing ability after relief. However, ardia musle from the -relieved group reovered only unloaded shortening veloity while the ability to sustain load remained depressed. We onlude that the reuperative potential of myoardium damaged by pressure overload is adequate provided ongestive heart failure has not ourred. Heart failure produes a persistent redution in fore-generating ability of the myoardium. Hypertrophy due to pressure overload, with or without, leads to ardia ateholamine depletion whih is not readily reversed by relief of the overload. oardial ateholamine stores following relief of a pressure overload, despite the linial relevane of suh information for the orret timing of therapeuti interventions. s ~ 9 Even less is known of fators that may determine the potential for return of ontratile funtion and norepinephrine stores. A reent study 10 has established that the ontratile defet of hypertrophy due to pressure overload without heart failure, produed by experimental pulmoni onstrition, is totally relieved after relief for approximately 4-5 weeks from the pulmoni stenosis. The mehanis of at papillary musle an be desribed in a manner similar to that employed for skeletal musle." It has been shown that the variation in mehanial musle funtion is small within different groups of ats, thus funtional parameters from different groups an be ompared quantitatively. 12 Sine it is possible by onstrition of the pulmonary artery in the at to produe right ventriular hypertrophy with and without overt ongestive heart failure, 1 a soure of myoardium from hypertrophied and failing hearts is available. In addition, surgial reversal of

2 42 CIRCULATION RESEARCH VOL. 40, No. 1, JANUARY 1977 the pressure overload is possible. In the present study, in addition to examining the reversibility of right ventriular hypertrophy and depressed myoardial funtion, 10 the potential for repletion of depleted norepinephrine stores was investigated. Methods Hemodynamis of the intat at, ontratile performane of isolated right ventriular papillary musles, and ventriular norepinephrine onentrations were assessed in five groups of ats: normal nonoperated ontrols (C); ats with pulmoni onstrition of a degree whih produed right ventriular hypertrophy without ongestive heart failure (); ats prepared as in but with the onstrition removed for 30 days (); ats with severe pulmoni onstrition produing ongestive heart failure as well as hypertrophy (); and ats prepared as in but with the pulmoni onstrition removed for 30 days (R). An additional group of ats reeived a pulmoni onstrition as in but did not have the stenosis relieved after 2 weeks as in the group. This group remained onstrited for an additional period whih was approximately equal to the relief period aorded to the group. Cats of either sex, weighing kg, were anesthetized with intravenous sodium pentobarbital (25 mg/kg). Suinylholine (1 mg/kg) was injeted intravenously and ventilation was supported by endotraheal positive-pressure ventilation. Cirular lips were plaed around the proximal main pulmonary artery under asepti onditions through a left interostal thoraotomy. The lumina of the onstrited portion of the pulmonary arteries averaged 30 % and 13 % of normal, with lips having average diameters of 3.5 mm and 2.8 mm, respetively. The lips with smaller diameters produed and the larger lips produed. It has been shown previously by histologial examination 1 that this method of produing right ventriular hypertrophy also auses hypertrophy of the assoiated papillary musles. Regular diet was maintained postoperatively. After days the ats were again anesthetized with sodium pentobarbital (25 mg/kg). Cannulas were plaed in the desending aorta through a femoral artery and in the right ventrile through the right external jugular vein. Right ventriular and aorti pressure was measured with Hewlett-Pakard (1280 series) pressure transduers. The zero referene point was taken at the midhest position with the ats supine. All signals were reorded on a multihannel Hewlett-Pakard (7888A) pressure ink osillograph. A ardia index (defined as ardia output/ body weight) was measured by the indiator-dilution tehnique employing thermal dilution. Saline (1 ml) at room temperature was injeted into the right ventrile and temperature was sampled in the proximal aorta with a thermoouple introdued through the left arotid artery. Following the hemodynami study, if the pulmoni band was to be removed, the left hest was opened at the 4th interostal spae and the pulmonary arterial onstrition was relieved. Any intrapleural fluid was withdrawn with a syringe. The hest was losed and the at was allowed to reover for 30 days. For ats from the nonreovery ( and ) and the ontrol (C) groups the hearts were rapidly exised and a papillary musle from the right ventrile was removed and transferred immediately to a myograph ontaining oxygenated Krebs' solution. The myograph has been desribed in detail previously. 13 The papillary musle was held at its nontendinous end by a lip attahed to a rigid pin. The pin penetrated the bottom of the myograph bath through a silione grease seal and was fixed to a Statham fore transduer (GI-4-25). The upper, tendinous, end of the musle was attahed to an isotoni lever for the measurement of musle shortening. The isotoni lever, mounted on an adjustable Palmer stand, ould be lamped in a fixed position, allowing the fore of isometri ontration to be measured. Musle length ould be ontrolled by adjusting the elevation of the fixed lever with the adjustable Palmer stand. When the lever was unrestrained and an appropriate load applied, the extent and veloity of shortening of the musle ould be determined at various preloads and afterloads. Thus both the length-tension and fore-veloity relations of the papillary musle were assessed. Fore, musle length, their time derivatives, and the stimulus artifat were reorded on a Hewlett-Pakard (7888A) multihannel osillograph. Musles were stimulated by an AEL stimulator with square wave pulses 5 mse in duration and with voltage limited to 15-25% above threshold; stimuli were delivered through field eletrodes plaed parallel to the vertial axis of eah musle. The limited stimulus strength prevented augmentation by release of ateholamines from the papillary musle stores. 14 Musle bath temperature was maintained at 30 C and ontration frequeny was 12/min. All studies were onduted after the musle had ontrated for at least 1 hour in the myograph and performane had beome stable. Preparations remained stable for a period exeeding that neessary for all studies (at least 3 hours). Effets of paired stimulation, inluding peak tension, maximum isometri dp/dt, and the time from stimulus to peak tension, were examined for the first ontration following the essation of paired stimulation whih had produed 12 augmented ontrations in whih the interpair-stimulus interval did not exeed by more than 20 mse the point at whih the tension response hanged from a simple augmented ontration to a doublehumped biphasi response. Musle length was determined at a preload approximately equal to that of the ontrol group at an absolute load of 0.4 g and at the apex of the length tension urve. The latter length was used to alulate ross-setional area and the former to express ontration veloity in musle lengths per seond. Fore-veloity urves representing a mean for eah group were obtained by a widely used method whih has never been desribed in the literature. The method of averaging shortening veloities at normalized loads of 0.5, 1.0,1.5 (et.) g/mm 2 onsists of plotting for eah papillary musle in a given group the fore-veloity urve at the atual loads employed. The absissae are then altered to reflet load normalization with respet to musle rosssetional area. The urves are drawn through the experimentally obtained points and the veloities at the desired loads are read off the urves to obtain the average for the group. An analogous proedure was employed for obtaining the mean length-tension urves.

3 RECUPERATIVE POTENTIAL IN HYPERTROPHY AND FAILURE/Coulson et al. 43 In onsideration of the fat that preload determines P o (the minimum load whih just preludes musle shortening) in the fore-veloity relationship, and sine musle ross-setional area is not measured until after the experiment, the atual area-normalized preloads are not known until after the experiment. To allow for variability arising in this manner, fore-veloity urves were obtained at absolute preloads of 0.2, 0.4, 0.6, and 0.8 g and the speifi urves used were seleted for the area-normalized preload whih most nearly approximated the preload of the ontrol group at an absolute preload of 0.4 g. After removal of the papillary musle the free wall of the ventrile was removed, blotted dry, and weighed; the interventriular septum was weighed together with the left ventrile. Within 2 minutes after exision of the heart, approximately one-half of eah ventrile, ut from base to apex and inluding half of the septum in the ase of the left ventrile, was frozen in liquid nitrogen for norepinephrine assay by a modified trihydroxyindoleaeti aid method. 4 The perentage of water in the ventriles was determined by weighing a portion of tissue before and after drying at 60 C for 72 hours. Left and right ventriular weights were expressed as ratios of the body weight at the time of papillary musle study. At the time of heart exision the 5-mm setion of pulmonary artery immediately above the pulmoni valves in the C,, and R groups was removed, ut longitudinally and flattened under a mirosope slide. The width dimension whih previously had been the irumferene was measured and the luminal ross-setional area was alulated aording to a right ylindrial model. In the two groups whih still had bands on at the time of study ( and ) the area was determined by inserting a suession of ylindrial metal probes of known dimensions through the arterial segment with the band still in plae. The diameter of the largest probe whih just fit was taken as the pulmonary arterial diameter. Sine the size of great vessels varies somewhat with body size, all ross-setional areas were normalized with respet to body weight (Table 1). DEFINITION OF EXPERIMENTAL GROUPS Congestive Heart Failure () In this group of ats the lumen of the pulmonary artery was redued to 13% of normal and the heart was studied days after onstrition. In reognition of the diffiulty of defining ongestive heart failure in absolute terms, and beause animal models of heart failure mimi but are not neessarily idential to linial heart failure, the following riteria were seleted to define the presene of : pleural effusion; asites; abnormally elevated right ventriular end-diastoli pressure (>7 mmhg). All ats in this group satisfied all riteria. Cardia index as already defined was measured for three ats from eah group and was low (<50 ml/min per kg) in the three ats for whih it was determined. Right Ventriular Hypertrophy without Heart Failure () This group of ats had the pulmonary arterial lumen redued to 30% of normal for days prior to study. Cats were inluded in this group only if they ould be exluded from the ategory of failure by the riteria outlined above. All ats in both and groups exhibited right ventriular systoli hypertension when ompared to normal ontrols (Tables 1 and 2). Pure Control vs. Sham-Operated Controls Spann et al. 4 found no signifiant differenes in the mehanial properties of papillary musles from shamoperated guinea pigs when ompared to normal. Thus, unoperated ats were onsidered suitable for ontrol of experimental mehanial properties in our investigation. Consideration was given to the question of myoardial norepinephrine onentration sine an earlier study 15 re- TABLE 1 Hemodynami Parameters of All Groups of Cats; Comparison of Experimental Croups with Normal Group R Group Pulmonary artery ross- Heart rate Aorti pressure RVEDP (mm Cardia index setional area (mm 2 /kg Body wt No. of ats (beats/min) (mm Hg) RVSP (mm Hg) Hg) (ml/min) wt) 3095 ± ± ± ± ± ± t ± ±14 272t ±8 248 ±18 199/149 ±12/9 148/107* ±5/6 178/134 ±10/7 174/127 ±8/8 192/133 ±12/ ± * ± ± * ± ± ± * ± ± ± ± ± * ± ± * ± ± ± ± ± ± ±0.54 Data are expressed as mean ± SEM. Cardia index was determined in three ats in eah group. See Methods for determination of pulmonary artery dimensions normalized with respet to body weight. RVSP = right ventriular systoli pressure; RVEDP = right ventriular end-diastoli pressure. C = ontrols; = ongestive heart failure; R = ongestive heart failure-relief group; = right ventriular hypertrophy; = right ventriular hypertrophy-relief group. * P < 0.01, signifiantly different from ontrol group. t P < 0.05, signifiantly different from ontrol group.

4 44 CIRCULATION RESEARCH VOL. 40, No. 1, JANUARY 1977 TABLE 2 Hemodynami Comparison of Relief Groups (R and ) prior to Relief of Stenosis with Corresponding Nonrelieved Groups ( and ) Heart rate (beats/ Aorti blood pres- RVEDP (mm Group No. of ats min) sure (mm Hg) RVSP (mm Hg) Hg) Congestive heart failure 5 R before relief of 5 stenosis Right ventriular hypertrophy 6 before relief of 4 stenosis 182 ± ± ±8 228t ±18 148/107 ±5/6 160/117 ±17/±11 174/127 ±8/±8 186/141 ±6/± ± * ± ± ± ± ± ± ±0.5 Data are expressed as mean ± SEM. RVSP = right ventriular systoli pressure; RVEDP = right ventriular end-diastoli pressure; group identifiations as in Table 1. * P < 0.05, signifiantly different from group. t P < 0.05, signifiantly different from group. ported that regional neural ablation resulted in depleted norepinephrine stores in the dog heart. However, shamoperated ontrols in the studies of Cooper et al. 15 and Chidsey et al. 16 showed no signifiant differenes in ardia norepinephrine onentration from that found in normal dogs. The same observation has been made in the guinea pig. 4 In view of these findings and in reognition of the fat that effetive, deliberate surgial ardia sympathetomy is ahieved only with virtual autotransplantation, 15 the unoperated at was onsidered to be adequate for ontrol experiments on myoardial ateholamine onentration. Attempted Regression of Right Ventriular Hypertrophy () and Congestive Heart Failure (R) These two groups of ats met the same riteria and were treated exatly as their orresponding nonreovery groups exept that after days of pulmoni onstrition they were studied hemodynamially, then had their onstriting lips removed and were allowed to reover for 30 days, at whih time they were studied as the other groups. An additional group, prepared initially as the and groups, was studied. In this extra group, however, after the 10- to 14-day period of onstrition the group was neither killed nor studied as in the group nor relieved of the onstrition as in the group. This group was provided in order to ontrol for the ontingeny of regression of hypertrophy without relief of the stenosis. Results BODY WEIGHTS The weights of the ats in the and groups were mathed at the onset and remained stable, exhibiting no signifiant (P > 0.1) gains or losses during the experiment. Similarly, the body weights of the and R groups were mathed initially and also did not develop differenes (P > 0.1) during the experiment. Body weight values of ats in the and groups were intermediate between C group and those of the and R groups. There was no signifiant hange in weight of ats within any group during the ourse of the experiment although there were differenes between groups (Table 1). Pleural and asiti fluid, withdrawn with a syringe from the group at the time of the study and from the R groups at the time of band removal, was responsible for less than 10% of total body weight. HEMODYNAMICS Hemodynami values for the two reversal groups, obtained just before removal of the lip, were omparable to the data for orresponding and groups as shown in Table 2 with the exeption that before relief of stenosis the right ventriular systoli pressure of the R group was less than the orresponding pressure in the group. It was, however, signifiantly higher (almost double) than the ontrol value (Tables 1 and 2). Table 1 summarizes and ompares the hemodynami parameters of all five groups of ats at the time of final study. Comparisons were made with an unpaired Student's /-test for populations with essentially similar variane (Ftest). Both the group and the group exhibited right ventriular systoli hypertension. The group had depressed systemi blood pressure when ompared with the C group. The values of systemi pressure in the group were less than ontrol, although the differene was not signifiant. The group exhibited an elevation of right ventriular end-diastoli pressure as well as a depressed ardia index. Both reovery groups, and R, had normal hemodynami parameters 30 days following band removal. VENTRICULAR WEIGHT AND TISSUE WATER Right ventriular weight always inreased after the onstriting operation (Table 3), whereas left ventriular weight was unaltered. The R ats ontinued to exhibit abnormally high right ventriular weight after the relief period. Ventriular weight in the R group was less than that found in the group. Cats from the group had normal right ventriular weights. Left ventriular tissue water did not vary from normal in any of the experimental groups. Right ventriular tissue water was normal exept for group with ongestive heart

5 RECUPERATIVE POTENTIAL IN HYPERTROPHY AND FAILVRE/Coulson et al. 45 TABLE 3 Heart Weight (HW)-Body Weight (BW) Ratios and Perentage Water of Left and Right Ventriles Groups R No. of ats Left ventrile HW/BW (g/kg) 2.06 ± ± ± ± ±0.16 % H 2O 76.3 ± ± ± ± ±0.6 Right ventrile HW/BW (g/kg) 0.52 ± * ± t ± * ± ±0.03 % H 2O 73.4 ± * ± ± ± ±0.9 Results are expressed as mean ± SEM. Group identifiation as in Table 1. * P < 0.01, signifiantly different from normal, by unpaired r-test. t P < 0.05, signifiantly different from normal. failure in whih it was slightly elevated. Table 3 summarizes these results. NOREPINEPHRINE CONCENTRATION Marked depression of the ardia norepinephrine onentration below that found in the normal group (P < 0.05) was observed in both right and left ventriles of all experimental groups. The normal (C group) value of norepinephrine onentration in the myoardium was 1.42 ± 0.29 /xg/g in the right ventriular free wall 1.35 ± 0.33 /xg/g in the ombined left ventriular free wall and septum. In hypertrophy ompliated by ongestive heart failure () the right and left ventriular values were 0.01 ± 0.02 and 0.72 ± 0.08 /xg/g, respetively. The R group was found to have ardia norepinephrine stores of 0.27 ± 0.09 and 0.63 ± 12 jxg/g in the right and left TENSION g/mm*4 *- IN- ACTIVE TENSION R ~Q 15} (5) (5)...]A RESTING TENSION ventriles, respetively. The orresponding values for hypertrophied nonfailing hearts () were 0.11 ± 0.03 /u.g/g and 0.72 ±0.14 /xg/g for the right and left ventriles, respetively. Cats reovered from hypertrophy without failure () had right and left ventriular norepinephrine onentrations of 0.21 ± 0.09 /xg/g and 0.61 ±0.14 /xg/g, respetively. MYOCARDIAL ISOMETRIC LENGTH-TENSION RELATIONSHIPS The length of the papillary musle at the apex of the length-tension urve was defined as L max, and hanges in length were expressed as perentages of L max. Tension (fore) was alulated as fore per unit of ross-setional area of musle. The ross-setional areas of normal (C) papillary musle averaged 0.94 ± 0.17 mm 2. The group was not signifiantly different from ontrol (P > 0.10) and averaged 1.25 ± 0.29 mm 2. The musles were signifiantly larger than ontrol (P < 0.01) and averaged 1.93 ± 0.26 mm 2. The R group had musles, signifiantly larger than ontrol (P < 0.05), averaging 1.62 ± 0.28 mm 2. The group had papillary musles not signifiantly different from ontrol (P > 0.10) and averaged 0.84 ±0.1 mm 2 in ross setion. Figure 1 illustrates the ative and resting length-tension (mean ± SEM) relationships of the various groups. Resting tensions were not signifiantly (P > 0.1) altered from normal in any group. While resting tension in the and groups appears high and that of the R group appears low, within group variation preludes definition of a signifiant differene between the means of these groups and the C group. Ative tensions were depressed at all lengths along the urves in both the and groups. The R group ontinued to exhibit a depressed length-ative tension relationship but the group was found to have a normal length-ative tension relationship. The isometri tension developed atively at the apex of i- [ > - 11) (6) 'd n LENGTH PERCENT CHANGE FROM LMAX LENGTH FIGURE 1 Ative and passive length-tension relationships of right ventriular papillary musles. Points on urves are means and error bars are ± / SEM. Solid and broken lines are ative and passive length-tension urves, respetively. Left panel: data from ontrol (C), ongestive heart failure (), and ongestive heart failure relieved (R) groups. Right panel: data from the same ontrol group as in the left panel, and from the right ventriular hypertrophy () and right ventriular hypertrophy relieved () groups. Parenthetial numbers are sample size (see text for numerial detail).

6 46 CIRCULATION RESEARCH VOL. 40, No. 1, JANUARY 1977 the length-tension urve was 6.06 ± 0.86 g/mm 2 in the normal ats (C). In the group this was redued from the value of C group to 2.78 ± 0.33 g/mm 2 (P < 0.01). The R group ontinued to exhibit redued (from the value of C group) developed tension at the apex of the length-tension urve and averaged 2.17 ± 0.29 g/mm 2 (P < 0.01). This value in the group was redued to 3.58 ± 0.49 g/mm 2 (P < 0.01). The group averaged 5.87 ± 0.31 g/mm 2, a value whih was not different from C group (P > 0.1). The tensions of the and groups were not different from eah other (P > 0.1). EQUIVALENT PAPILLARY MUSCLE CROSS-SECTIONAL AREAS Beause the ross-setional areas of the papillary musles from the and R group were signifiantly greater than those found in the other three groups, the signifiane of the depressed isometri maximum tension in these two groups warranted further examination. Subgroups from these two experimental groups, seleted speifially for small ross-setional areas, were ompared with a randomly seleted subset obtained from the normal ontrol group. The subset seleted from the normal (C) group inluded musles whose ross-setional area averaged 1.21 mm 2 and whih developed peak isometri tension that averaged 5.74 ± 0.65 g/mm 2 (n = 3). The group subset had papillary musle ross-setional areas that averaged 1.26 ±0.12 mm 2 ; this value was not signifiantly different (P > 0.10) from that of the ontrol subset but peak isometri tension, the average value of whih was 3.70 ± 0.25 g/mm 2 (n = 2), was nonetheless signifiantly less (P < 0.05) than that of the normal subset. Similarly, a VELOCITY L/s A A R (5) (5) (5 R subset (n = 2) with papillary musle ross-setional areas averaging 1.11 ± 0.25 mm 2 [not signifiantly different (P > 0.10) from the normal subset] had a peak isometri tension of 2.08 ± 0.77 g/mm 2, a value signifiantly less (P < 0.05) than the normal subset value. The subset tension was not signifiantly different from that of the R subset (P > 0.1). FORCE-VELOCITY RELATIONS Figure 2 illustrates the fore-veloity (mean ± SEM) urves for the various groups. Maximum veloity of shortening was assessed at 0.5 g/mm 2 (Vmax.5) in order to avoid extrapolation of the urves to zero load. Veloity was expressed in musle lengths per seond (L/se). L was the length of the musle at the preload losest to that of ontrol musles at an absolute preload of 0.4 g. Fore was expressed in g/mm 2 of ross setion. The values of the area-normalized preloads for the various groups were: C, 0.43 ± 0.06 g/mm 2 ;, 0.48 ± 0.09 g/mm 2 ; R, 0.49 ± 0.07 g/mm 2 ;, 0.41 ± 0.05 g/mm 2 ; and, 0.48 ± 0.05 g/mm 2. None of these values was signifiantly different from ontrol or any other group (P > 0.1). Mean veloities were obtained by averaging veloities at speifi levels of area-normalized load. For the normal group (C) Vmax.5 was 0.90 ± 0.07 L/se. In the group Vmax.5 was redued to 0.30 ± 0.02 L/se (P > 0.01). The R group exhibited a normal Vmax.5 of 0.82 ± L/se (P > 0.25). In the group Vmax.5 was redued to 0.50 ± 0.07 L/se (P < 0.01). Vmax.5 in the group was a value not different from normal ontrols and averaged 1.12 ± 0.13 L/se (P > 0.10). The lightest load at whih the musle failed to shorten A (5) (6) 14) LOAD 2 3 LOAD g /mm z FIGURE 2 Fore-veloity relationships of right ventriular papillary musles. Points on urves are means and error bars are ± 1 SEM. Veloity is in musle lengths per seond (L/s). Load- (fore) is normalized for ross-setional area. The left panel ompares C group with the and R groups. The right panel ompares the same C group with the and groups. Note the R urve whih has depressed isometri load but normal unloaded veloity of shortening (see text for detail). Abbreviations as in Figure 1.

7 RECUPERATIVE POTENTIAL IN HYPERTROPHY AND FAILURE/Coulson et al. 47 (P o ) for the normal musles (C) was 4.64 ± 1.29 g/mm 2. In the group P o was redued to 2.04 ± 0.28 g/mm 2 (P < 0.05) as it was for the group, 2.00 ± 0.25 g/ mm 2 (P < 0.05). The R musles demonstrated severely redued values of P o, 1.22 ± 0.16 g/mm 2 (P < 0.025) despite the return of Vmax.5 to normal. Conversely, the musles demonstrated P o values unhanged from ontrol, 5.14 ± 1.07 g/mm 2 (P > 0.10), in onert with the return of Vmax.5 to normal. AUGMENTATION OF MYOCARDIAL CONTRACTILE FUNCTION-PAIRED ELECTRICAL STIMULATION Table 4 ompares peak isometri tension (P k ), maximum dp/dt, and time from stimulus to peak tension (TTP k ), all of whih varied from the normal ontrol values in every group exept the group. In the R group, the TTP k for a single stimulus was not signifiantly inreased over the normal (P > 0.1) although the time to peak tension after paired stimulus was still prolonged (P < 0.01). The differene between single and paired stimulation values for P k and maximum dp/dt, respetively, produed by paired stimulation, were signifiantly redued from the normal (C) values of 3.25 ± 0.39 g/mm 2 and ± 6.22 g/mm 2 per se in both the group [2.06 ± 0.43 g/mm 2 (P < 0.01), and ± 4.34 g/mm 2 per se (P < 0.01)] and the group [1.40 ± 0.42 g/mm 2 (P < 0.05), and ± 4.31 g/mm 2 per se (P < 0.01)]. For the R group the inrements were only 0.88 ± 0.39 g/mm 2 (P < 0.01) and 9.03 ± 4.19 g/mm 2 per se (P < 0.05). The inrements for the group were normal [3.76 ± 0.86 g/mm 2 (P > 0.1) and ± 8.25 g/mm 2 per se (P > 0.1)]. The normal (C) derement in the time from stimulus to peak tension (TTP k ) produed by paired stimulation was 58 ±15 mse. The derement in TTP k did not differ signifiantly from ontrol at the P = 0.05 level in any of the other groups:, 85 ± 18 mse; R, 42 ± 11 mse., 79 ± 21 mse;, 67.5 ± 8 mse. CONDITION OF RELIEF GROUPS PRIOR TO RELIEF OF STENOSIS Consideration was given to the question of the similarity of ondition between the and the ats and their orresponding relief groups ( and R). Table 2 shows for ats in the R group just prior to band removal, hemodynami parameters that were not signifiantly different from those of the ats. Similarly, the ats in the group, at the time of relief, had hemodynami parameters that were not signifiantly different from those of the group, with the exeption of heart rate, whih was lower in the group. The right ventriular systoli pressure of the R group before relief of stenosis was less than the orresponding pressure in the group. It was, however, signifiantly higher (almost double) than the ontrol (Table 2). COMPARISON BETWEEN CONTRACTILE PARAMETERS OF PAPILLARY MUSCLES OF GROUP AND A GROUP NOT RELIEVED OF PULMONIC STRESS FOR A TOTAL TIME SIMILAR TO THE SUM OF THE CONSTRICTED PERIOD PLUS THE RECOVERY PERIOD Table 5 illustrates that ontratile funtion, haraterized by the parameters of P k, dp/dt, and Vmax.5, was depressed in a group of musles obtained from ats treated similarly to the group but in whih the pulmoni onstrition remained in plae for an additional period similar in duration to the relief period of the group. Disussion Little is known of the fators that influene the degree of return to normality following relief of pressure overload. It would be helpful to know whether there is a gradual derease in the reuperative potential of depressed pressure-overloaded ventriular musle as severity of overload inreases or whether there is a sudden "break point" beyond whih reovery is minimal. The studies desribed in this paper indiate that the mehanially depressed, hypertrophied, but nonfailing right ventrile reovers normal mehanial funtion and weight after relief of pressure overload. This finding onfirms the work of Cooper et al. 10 The extension of this study to the failing, hypertrophied right ventrile, however, indiates that a more lasting defet ours when heart failure is a ompliating fator. SEVERITY OF PRESSURE OVERLOAD STRESS In the present investigation the more severe stress (87% onstrition of the pulmonary artery), whih superimposed ongestive heart failure on a bakground of right ventriular hypertrophy, was not assoiated with reovery of full ontratile funtion in the 30-day relief period. A Deriod of 30 days, however, was suffiient for full reovery of ontratile funtion in the ase of the less severe stress TABLE 4 Effets of Sustained Post-extrasystoli Potentiation on Peak Tension (Pk), Maximum dp/dt, and Time to Peak Tension (TTP k ) of Right Ventriular Papillary Musle P k dp/dt (g/mm 2 )/se TTP k Group R Single 6.28 ± ± 0.20* 2.70 ± 0.29* 3.12 ± 0.53* 5.87 ± 0.31 Paired 9.53 ± ± 0.69t 3.58 ± 0.63* 4.52 ± 0.80* 9.63 ± 0.72 Single ± ± 1.03* 9.03 ± 1.06* ± 2.00* ± 4.45 Paired ± ± 5.33* ± 2.99* ± 5.98* ± 5.33 Single 340 ± ± 15* 388 ± ± 16* 355 ± 5 Paired 282 ± ± 17* 346 ± 10* 363 ± 28* ± 10 Results are expressed as mean ± SEM; group identifiations as in Table 1; TTP k * Signifiantly different from ontrol (P < 0.01). t Signifiantly different from ontrol (P < 0.05). time from stimulus to peak tension.

8 48 CIRCULATION RESEARCH VOL. 40, No. 1, JANUARY 1977 TABLE 5 Comparison between Contratile Parameters of Papillary Musles of Group and a Group Not Relieved of Pulmoni Stress for a Total Time Similar to the Sum of the Banded Period plus the Reovery Period Group No. of RV wt/body wt ats Body wt (g) (g/kg) Weeks banded Weeks unbanded Total weeks after banding Papillary musle ross-setional area (mm 2 ) P k (g/mm 2 ) dp/dt (g/mm 2 ) Vmax.5 (L/se) Unrelieved group P values for omparison between and unrelieved group ± 214 NS, P > ±0.03 l.o5±o.o7 P < NS,P> ± ±0.47 P < ± ±2.90 P < P < 0.01 Values are given as means ± SEM. = right ventriular hypertrophy-relief group; Vmax.5 = maximum veloity of shortening [in musle lengths per seond (L/se)] at 0.5 g/mm! ; P k = maximum isometri fore. (70% onstrition of the pulmonary artery) whih produed the same degree of right ventriular hypertrophy but not ongestive heart failure. A hypertrophy stimulus of 2 weeks' duration was used beause, due to permanent vessel sarring, it has not been possible, in this laboratory, to remove a pulmonary artery onstrition of greater severity than 70% after more than 2 weeks without some residual stenosis persisting. Cooper et al. 10 have suessfully unbanded animals after 3-4 weeks with an experimental stenosis similar to the and groups in our present work. Their results after 3-4 weeks of banding were essentially idential to those in our present work. However, in their study 10 no attempt was made to produe pulmoni onstrition of the severity produed in the and R groups of the present work. RECOVERY FROM CONGESTIVE HEART FAILURE AND RIGHT VENTRICULAR HYPERTROPHY Despite resumption of normal right heart pressures, reovery of resting ardia pump funtion, and absene of residual stenosis (Table 2) after removal of the onstriting lip, the mehanial ontratile properties of the R group remained severely depressed after the 30- day reovery period. The length-tension urve (Fig. 1), P o (the isometri point in the fore veloity relation), and the isometri parameters (P k, dp/dt, and TTP k ), all remained depressed in the R group (Table 4). The ontinued depression of the ontratile funtion in the R group is in marked ontrast to the return to omplete normality of mehanial ontratile funtion observed in the ats of the group whih had the same degree of right ventriular hypertrophy but in response to a less severe pulmoni onstrition and with no. Sine the ats reovered ompletely normal heart weight, but those in the R group did not although the degree of initial hypertrophy was the same for both (Table 3), the degree of hypertrophy per se annot be responsible for the different reuperative performanes of the two groups of ats. Sine all the ats resumed normal ardia funtion after a relief period of 30 days, it would not be illogial to assume that ats subjeted to less severe onstritions would also reover under similar irumstanes. Above the 70% onstrition there does, however, appear to be a "break point" in reserve and reuperative potential of the musle, beause all ats subjeted to the more severe stress of an 87% pulmoni onstrition presented with symptoms of ongestive heart failure and failed to reover normal ontratile funtion despite idential relief of the experimental damaging stimulus. In view of an observation" that the depressed myoardial ontratile funtion of the pressure-overloaded at heart reovers with time without relief of the pressure overload or regression of hypertrophy, it was neessary to exlude the possibility that reovery of ontratile funtion in the group would ultimately have ourred, anyway, without relief of the pressure overload. If the group had not been unbanded after 14 days, would the reovery of funtion have ourred nonetheless, after a total of 44 days? Aordingly, a omparison was made between the behavior of musles from the group and from a group of seven ats whih had been subjeted to the same degree of pulmoni onstrition as the group but whih had not been relieved of the pulmonary stress after 14 days. The musles of this group were studied after 7.0 ± 0.43 weeks, a period approximately equal to the 6.3-week total of the onstrition and relief periods in the group. Sine the ontratile parameters of the unrelieved group remained depressed and those of the group reovered (Table 5), the possibility mentioned is exluded. THE NATURE OF LESIONS DEPRESSING CONTRACTILE PERFORMANCE The same depressed ontratile parameters haraterized the hypertrophied papillary musles from ats whether they had an 87% pulmoni onstrition and ongestive heart failure or a 70% pulmoni onstrition and no ongestive heart failure. The fat that the former group failed to reover and the latter group did reover suggests that the failure group may have been an example of a more advaned depression, similar in nature but resulting from a more severe stress stimulus. However, the return of Vmax.5 to normal in the R group with persistene of depressed P o (Fig. 2) is in marked ontrast with the omplete reovery of the group whih had been depressed but had not presented with ongestive heart failure. This observed disrepany permits some speulation about the lesions whih may be involved in ongestive heart failure and whih ould ontribute to the poor musle funtion. All the ontratile depression observed in both the group and group ats (Table 4) ould be

9 RECUPERATIVE POTENTIAL IN HYPERTROPHY AND FAILVRE/Coulson etal. 49 explained by failure of any of a variety of mehanisms whih lead to inomplete ativation of the ontratile mehanism. In the reent study by Cooper et al. 10 of pure hypertrophy reversal, the depression of ontratile funtion was assoiated with an observed abnormality of state 4 mitohondrial respiration whih has been linked to alium ion transport. 18 It reently has been demonstrated 19 that rabbit papillary musles depressed by pressure overload hypertrophy developed the same amount of tension as normal musles when the sarolemma was rendered permeable by glyerination, and the ontratile mehanism was ativated by externally applied Ca 2+. This finding is onsistent with a lesion assoiated with the pressure overload whih redues effetive alium ativation of the ontratile mahinery but does not modify the atual ontratile mehanism itself. However, in our present study, the R group had papillary musles whih ontrated with normal veloity at low loads (Fig. 4) but had little apability for fore development. This is a ondition onsistent with a redued number of effetive ontratile units whih are nonetheless adequately ativated. In terms of the sliding filament theory of musle ontration this ould represent normal funtion of ontratile mahinery with far less than the normal numbers of ontratile units operating. The impliation is that myoardium from animals with ongestive heart failure as well as right ventriular hypertrophy was the subjet of a double lesion whih redued both ontratile ativation and effetive numbers of partiipating ontratile units, suh that when the reovery period was over (30 days) the ativation defet had been orreted but the depleted numbers of effetive ontratile units had not been restored. Cooper et al. 10 have also demonstrated that ardia musle from ats with right ventriular hypertrophy but no signs of ongestive heart failure reovered normal funtion after a similar relief period. This reovery would not prelude the sort of double lesion invoked to explain the behavior of musles from the R group if suh a double lesion were repaired in less time when the initiating stress had been less severe. The work of Henry et al. 19 provides evidene that the presene of a double lesion affeting both the aliumativating mehanism and the ontratile mehanism is unlikely in hypertrophied but nonfailing heart musle. In that study 19 hypertrophied musles biologially ativated after experimental eletrial stimulation developed subnormal fore but exhibited a fore development potential equal to that of normal musles when artifiially ativated with external alium. This is in ontrast with the musles of the R group in the present work whih appeared to have adequate ativation, as evidened by normal shortening veloity at low loads, but little potential for fore development assessed as either P o or P k. Sine the essential differene between the R group and the group was the presene of ongestive heart failure we onlude that in and R before the relief period there was a defet of both the ativation mehanism and the ontratile mahinery while in and before reovery the ativation mehanism was the prinipal limiting fator. DEPLETION OF NOREPINEPHRINE STORES The ateholamine stores of both the left and right ventriles were depleted in both the and groups. Neither of the orresponding reovery groups ( and R) demonstrated normal norepinephrine stores. Sine the left ventriles were never hypertrophied but exhibited a redution in norepinephrine store, both hypertrophi strutural hanges and a mass-dilution effet an be eliminated as likely soures of the adrenergi lesion evidened by ateholamine store depletion. The importane of the persistene of this adrenergi lesion annot be ignored, sine it suggests that an important soure of ontratile augmentation potential afforded neurogenially by the sympatheti nervous system may be denied the weakened heart during the reovery whih is possible after relief of a hroni pressure overload. Referenes 1. Spann JF Jr, Buino RA, Sonnenblik EH, Braunwald E: Contratile state of ardia musle obtained from ats with experimentally produed ventriular hypertrophy and heart failure. Cir Res 21: , Spann JF, Covell JW, Ekberg DL, Sonnenblik EH, Ross J Jr, Braunwald E: Contratile performane of the hypertrophied and hronially failing at ventrile. Am J Physiol 223: , Rutenberg HL, Spann JF Jr: Alterations of ardia sympatheti neurotransmitter ativity in ongestive heart failure. Am J Cardiol 32: , Spann JF, Chidsey CA, Pool PE, Braunwald E: Mehanisms of norepinephrine depletion in experimental heart failure produed by aorti onstrition in the guinea pig. Cir Res 17: , Vogel JHK, Joobowitz D, Chidsey CA: Distribution of norepinephrine in the failing bovine heart. Cir Res 24: 71-84, Krayenbuehl HP, Brunner HH, Steiger U, Senning A: Effets of orretive valve surgery on ontratility in aorti stenosis. Cirulation 48 (suppl IV): 105, Ross J Jr, Sobel BE: Regulation of ardia ontration. Ann Rev Physiol 34: 47-90, Gault JH, Covell JW, Braunwald E, Ross J Jr: Left ventriular performane following orretion of free aorti regurgitation. Cirulation 42: , Simon JK, Lee SJK, Haraphongse M, Callaghan JC, Rossal RE, Fraser RS: Hemodynami hanges following orretion of severe aorti stenosis using the Cutter-Smiloff prosthesis. Cirulation 42: , Cooper G IV, Satava RM, Harrison CE, Coleman HN: Normal myoardial funtion and energetis after reversing pressure overload hypertrophy. Am J Physiol 226: , Sonnenblik EH: Impliations of musle mehanis in the heart. Fed Pro21: , Spann JF Jr, Sonnenblik EH, Cooper T, Chidsey CA, William VL, Braunwald E: Cardia norepinephrine stores and the ontratile state of heart musle. Cir Res 19: , Sonnenblik EH: Fore-veloity relations in mammalian heart musle. Am J Physiol 202: , Koh-Weser J: Role of norepinephrine release in the interval-strength relationship of heart musle. J Pharmaol Exp Ther 150: , Cooper T, Gilbert JW, Bloodwell RD, Crout JR: Chroni extrinsi ardia denervation by regional neural ablation. Cir Res 9: , Chidsey CA, Kaiser GA, Sonnenblik EH, Spann JF, Braunwald E: Cardia norepinephrine stores in experimental heart failure in the dog. J din Invest 43: , Williams JF, Potter RD: Normal ontratile state of hypertrophied myoardium after pulmonary artery onstrition in the at. J Clin Invest 54: , Drahota Z, Caratoli E, Rossi CS, Gamble RL, Lehninger AL: The steady state maintenane of aumulated Ca ++ in rat liver mitohondria. J Biol Chem 240: , Henry P, Ahumada GG, Friedman WF, Sobel BE: Simultaneously measured isometri tension and ATP hydrolysis in glyerinated fibers from normal and hypertrophied rabbit heart. Cir Res 31: , 1972