Effect of the Angiotensin II Blocker 1-Sar-8-Ala-Angiotensin II on Renal Artery Clip Hypertension in the Rat

Transcription

1 Effect f the Angitensin II Blcker 1-Sar-8-Ala-Angitensin II n Renal Artery Clip Hypertensin in the Rat By Graham J. Macdnald, Graham W. Byd, and W. Stanley Peart ABSTRACT Twenty-fur cnscius male Wistar rats, with hypertensin induced by left renal artery clipping (tw-kidney hypertensin) were infused intravenusly with l-sar-8-ala-angitensin II a cmpetitive angitensin II antagnist. The spectrum f respnses was wide, ranging frm a mild elevatin in bld pressure t a marked fall in bld pressure, despite effective and specific angitensin blckade in all cases. The change in bld pressure during l-sar-8-ala-aii infusin activity shwed a significant crrelatin with the level f plasma renin prevailing immediately befre the infusin (r = , P < 0.01) but nt with the prevailing bld urea level (r = 0.27, 0.1 > P> 0.05), the degree f hypertensin (r = 0.42, 0.1 > P > 0.05), r the time since clipping (r = 0.02, P > 0.05). There was n significant crrelatin between the degree f hypertensin and the plasma renin activity (r = 0.42, 0.1 > P > 0.05). In rats with bld pressure drps > 20 mm Hg in respnse t l-sar-8-ala-aii, the final bld pressure level was still abve the nrmtensive range. Excisin f the clipped kidney reduced bld pressure t nrmal r t near nrmal within 24 hurs in all f the rats tested. It is cncluded that the degree f dependence f renal hypertensin n the renin-angitensin system is directly related t the increase in circulating angitensin itself and nt t an increase in sensitivity t angitensin. Other factrs appear t be invlved in renal clip hypertensin in additin t circulating renin and angitensin, especially when the measured activity f plasma renin is nrmal. The develpment f specific cmpetitive antagnists t angitensin II has prvided a means f assessing the imprtance f renin and angitensin in the maintenance f experimental renal hypertensin (1, 2). Studies utilizing such an inhibitr, l-sar-8-ala-angitensin II, have, hwever, yielded cnflicting results. Pals and c-wrkers (2) in their riginal studies fund a significant hyptensive effect f the drug in the first 2 weeks after the inductin f tw-kidney hypertensin by artic ligatin between the renal artery rigins. During the chrnic phase (4-5 weeks after inductin), infusin f the inhibitr had n significant effect. In cntrast, Brunner and cwrkers (3) shwed a significant mean fall in bld pressure in a grup f six tw-kidney hypertensive anesthetized rats given l-sar-8-ala-aii, but they culd nt demnstrate this effect in a similar grup f ne-kidney rats. Bing and Nielsen (4) fund a variable hyptensive effect during infusin f 1- Sar-8-Ala-AII int ne- and tw-kidney renal hypertensive rats, bth cnscius and anesthetized. Frm the Medical Unit, St. Mary's Hspital Medical Schl, Lndn W.2, United Kingdm. Please address reprint requests t G. J. Macdnald, University f New Suth Wales, Schl f Medicine, Prince Henry Hspital, Little Bay, N.S.W., 2036, Australia. Received Octber 21, Accepted fr publicatin August 11, The present study was undertaken t examine the nature, extent, and pssible reasns fr the variability in the respnse t l-sar-8-ala-aii in tw-kidney hypertensin in the rat between 2 and 12 weeks after clipping, taking int accunt such factrs as the time since clipping, the plasma renin levels, the severity f the hypertensin, and the degree f impairment f renal functin. Since acute surgery and anesthesia may have intrduced sme unwanted variability in previus studies (4), all f ur experiments were perfrmed in cnscius rats studied 2 days after the implantatin f arterial and venus catheters. Methds INDUCTION OF HYPERTENSION Male white Wistar rats weighing g were anesthetized with ether, and the left renal artery was cnstricted with a preset silver clip with an internal gap f 0.2 r 0.25 mm. After 1-2 weeks, bld pressure measurements were cmmenced using the micrphnic methd f Friedman and Freed (5). Additinal grups f rats were subjected t sham-clipping: the left renal artery was expsed, and a silver strip was placed in the perinephric fat. Thrughut the experiments, the rats were fed a regular pellet diet (Oxid SG10) and given free access t tap water. N attempt was made t cntrl sdium intake, since it has been shwn that sdium status may be an imprtant determinant f the renin levels achieved in this frm f hypertensin (6, 7); we wished t study hypertensive rats with spntaneusly achieved variables. Circulatin Research, Vl. 37, Nvember 1975

2 1 Sar 8-Ala-AII AND RENAL ARTERY CLIP HYPERTENSION 641 ADMINISTRATION OF 1 Sar 8 Ala All Rats with established hypertensin (systlic bld pressure ver 200 mm Hg by tail measurements) were prepared fr the experiment by inserting tapered plyethylene catheters int their right internal and external jugular veins and their right cartid artery under sdium pentbarbital anesthesia. The catheters were filled with heparinized saline, plugged, and implanted subcutaneusly dwn the rats' backs. After a recvery perid f 2 days, the catheters were recvered, and the arterial line was cnnected t a pressure transducer and a Devices tw-channel recrder. Bld (0.5 ml) was then taken fr the estimatin f plasma renin activity. After the bld pressure had stabilized, dse-respnse curves t 5-Ile-angitensin II (infused at 0.05, 0.1, and 0.2 Atg/kg min" 1 ) and Z-nrepinephrine (Levphed, Winthrp) (injected in dses f ng) were btained. A base-line bld pressure trace f at least 30 minutes was then recrded, and l-sar-8-ala-aii 1 was subsequently infused at 4 /ig/min (a slutin f 133 Mg/ml in nrmal saline infused using a Meltec syringe pump at 0.03 ml/min). After 30 minutes f infusin, All blckade was cnfirmed by the lss f the pressr respnse t an All infusin at 0.2 Mg/kg min" 1, and the nrepinephrine dse-respnse curve was repeated. After an additinal minutes, the l-sar-8-ala-aii infusin was stpped, but the bld pressure recrding was cntinued until a steady level had been regained fr 30 minutes. At the end f such studies, 15 f the rats were anesthetized with a small dse f intravenusly administered sdium pentbarbital, and the left (clipped) kidney was excised in 11 rats. In the remaining 4 rats, a sham-nephrectmy was perfrmed (expsure and brief manipulatin f the left kidney). The fllwing day, direct bld pressure measurements were again made in a cnscius state, and the fur sham-nephrectmized rats were reanesthetized and subjected t a left nephrectmy. Their bld pressures were measured directly again n the fllwing day. PLASMA RENIN ACTIVITY MEASUREMENTS Bld (0.5 ml) was taken frm the arterial catheter int a heparinized tube standing in ice. Fllwing centrifugatin at 2,050 g fr 10 minutes at 4 C, 0.2 ml f plasma was added t 0.02 ml f 0.3M ethylenediaminetetraacetic acid (EDTA) and 0.01 ml f 0.2M 2,3-dimercapt-l-prpanl (BAL) and incubated at 37 C fr 4 hurs. The incubate was diluted t 1 ml with immunassay buffer, heated t 85 C fr 10 minutes t stp the reactin, and then frzen. Fr assay, the samples were thawed and centrifuged, and the supernatant fluid was assayed directly by the methd f Byd et al. (8) using 5-Ile-angitensin I as the standard. Recvery f 60 ng f 5-Ile-AI added t the riginal plasma sample was 83.4 ± 6.1% (SE). Assay f replicate samples gave a within-assay cefficient f variatin f 3%. In separate experiments, it was established in nrmal and hypertensive rats that bleeding f this amunt f bld did nt result in an increase in plasma renin activity in bld taken 1 hur later. 1 Generusly supplied by Dr. A. Castallin f the Nrwich Pharmacal Crp. Circulatin Research, Vl. 37, Nvember 1975 STATISTICAL ANALYSIS Significance testing was based n duble-tailed Student's t-testing r crrelatin cefficient calculatins. Base-line bld pressures were calculated by taking the average f the mean bld pressure at 1-minute intervals ver the 30 minutes immediately befre the start f the l-sar-8-ala-aii infusin. Mean bld pressure was calculated as the diastlic pressure plus ne-third f the pulse pressure. The mean bld pressure change induced by the l-sar-8-ala-aii infusin was taken as the difference between the base-line bld pressure and the average f the readings between 20 and 30 minutes after the start f the infusin. Results 90" On the day f the experiment, directly measured mean bld pressure varied frm 108 t 127 mm Hg in the 9 sham-clipped rats and frm 131 t 227 mm Hg in the 24 clipped renal hypertensive rats. The tw grups were f cmparable weight at the time f the experiment; the sham-clipped rats weighed 313 ± 31 (SD) g and the hypertensive rats weighed 335 ± 55.4 g. Plasma renin activities in the sham-clipped rats ranged frm 1.1 t 5.5 ng Al/ml hur" 1 (mean 3.0 ± 1.58 [SD] ng Al/ml hur" 1 ) and in the hypertensive grup (N = 22) frm 4.2 t 85 ng Al/ml hur" 1 (mean 20 ± 18.2 ng Al/ml hur 1 ) (Fig. 1). Infusin f l-sar-8-ala-aii at 4 jig/min resulted in cmplete blckade f the pressr effects f 5-Ile- AII infused at 0.2 fig/kg min" 1 in 19 rats (Fig. 2). In the remaining 5 rats, the maximum respnse was 10 mm Hg, a respnse indistinguishable frm the slight spntaneus fluctuatins in base-line bld pressure. The average mean bld pressure respnse t this dse f 5-Ile-AII prir t l-sar-8-ala- 80- (ngal/ml/hr) Plasma 40 " Renin Activity Mean ^ / * 0 Nrmal (n=27)2kidneyht(22) Sham clip (n-9) FIGURE 1 Plasma renin activity in nrmal, tw-kidney hypertensive (HT), and sham-clipped rats. Open circles in the hypertensive grup represent rats whse mean bld pressures fell by mre than 20 mm Hg during angitensin II blckade with l-sar-8-ala-aii.

3 642 MACDONALD. BOYD. PEART mm Hfl Angkrtensin II dse (pg/kg/min) 0,1 V 02? in Nrepinephrine dse (ng) FIGURE 2 Dse-respnse curves t infusins f 5-Ile-AII (squares) and injectins f l-nrepinephrine (circles) befre (pen symbls) and during (clsed symbls) infusin f l-sar-8-ala-aii. All symbls = means ± SE. A B.P. = change in mean bld pressure. All administratin was 34 ± 2.1 (SE) mm Hg. During l-sar-8-ala-aii infusin it was 1.3 ± 1.4 mm Hg. Figure 2 als shws that the respnse t /-nrepinephrine injectins was unimpaired. The bld pressure respnse t l-sar-8-ala-aii varied widely frm rat t rat. In 3 rats bld pressure fell by 5 mm Hg r less, and in 4 it actually rse slightly. In the ther 17 rats, falls in bld pressure varied cntinuusly up t a maximum f 65 mm Hg. The maximum average fall in bld pressure fr the whle hypertensive grup was 18 ± 3.5 (SE) mm Hg between 21 and 25 minutes f infusin. This decline was significant (P < 0.01), but, as seen in Figure 3, it was less than the fall bserved 24 hurs after the excisin f the clipped kidney even in thse rats shwing greater declines (> 20 mm Hg) with l-sar-8-ala-aii (P < 0.05). During l-sar-8- Ala-AII infusin, nly fur rats achieved bld pressures within the nrmal range bserved in sham-perated rats. In all f the rats subjected t left nephrectmy, bld pressure fell t within the sham-clipped range within 24 hurs, regardless f the respnse previusly seen t All blckade with l-sar-8-ala- AII. This fall was nt a result f anesthesia and surgery, since fur rats subjected t sham-nephrectmy failed t shw a fall in bld pressure at 24 hurs but subsequently did return t nrmal bld pressure fllwing excisin f the clipped kidney (Fig. 3). Varius factrs were analyzed t determine the basis fr the variatin in the individual respnses t l-sar-8-ala-aii (Table 1). There was n significant crrelatin with the bld urea level at the time f study (r = 0.27, P > 0.05), the time since clipping (15-80 days) (r = 0.02, P > 0.05), r the degree f hypertensin indicated by average baseline bld pressure measured directly n the day f the experiment (r = 0.42, P > 0.05). Plasma renin levels in the hypertensive grup were significantly higher than thse in the shamclipped cntrl grup cnsidered as a whle (P < 0.01) (Fig. 1). When the hypertensive rats were divided int thse with marked falls in bld pressure (> 20 mm Hg) and thse with lesser falls, the plasma renin activity in the frmer grup was significantly higher (P < 0.01) (Fig. 1). Plasma renin activity in bth grups was significantly higher than that in the sham-clipped cntrl rats (P < 0.01 fr the grup with the lwer bld pressure fall [13 ± 10 (SD} ng Al/ml hur"', N = 13] and P < fr the grup with a fall > 20 mm Hg [34.4 ± 20.5 ng Al/ml hur" 1, N = 9]). The fall in bld pressure during l-sar-8-ala-aii infusin shwed a highly significant crrelatin with the lg f plasma renin activity (Fig. 4) (r = 0.78, P < 0.01). In additin, the regressin line intercepted the zer pint n the y-axis at a plasma renin activity f 5.7 ng Al/ml hur" 1, within the nrmal range but just abve the upper limit f values btained in the sham-clipped rats. This fact suggests that tw-kidney hypertensive rats with a mmhg 140 Mean B.R i ft Mean ±SEM ft 80 n= 14 ' 2 8 ' 10 i 2 7 B.R fall<20mm Hg B.P.fall>20mm Hg FIGURE 3 Effects f l-sar-8-ala-aii (P113) infusin cmpared with thse f excisin f the ischemic kidney in rats shwing mre than and less than a 20-mm Hg fall in bld pressure with l-sar-8-ala- AII. Nte the difference in bld pressure (B.P.) even in thse rats with the larger declines (P < 0.05). Nte als in the ther grup that the bld pressure fllwing recvery' is cmparable t base-line bld pressure, i.e., the failure t induce a fall in bld pressure is prbably nt due t an intrinsic pressr effect f l-sar-8-ala-aii r t reflex stimulatin f renin secretin by l-sar-8-ala-ah. Circulatin Research, Vl. 37, Nvember 1975 lil (D 1

4 1-Sar-8-Ala-AII AND RENAL ARTERY CLIP HYPERTENSION 6 Data Used in Statistical Analysis f the Results TABLE 1 Rat Initial B P (mm Hg) ABP (mm Hg) Bld urea (mg/looml) Days since clip PRA (ng Al/ml hur" 1 ) A ar (mm Hg) There is a lack f crrelatin between the change in bld pressure (A BP) and the initial bld pressure (BP) (r = 0.42, P > 0.05), the bld urea level (r = 0.27, P > 0.05), and the days since clipping (r = 0.02, P > 0.05). The crrelatin between the bld pressure change and plasma renin activity (PRA) is shwn in Figure 4. r 0.78 p<o Plasma Renin Activity FIGURE (ng Al/ml/hr) Regressin line between the lg f plasma renin activity and the change in bld pressure (A B.P.) during l-sar-8-ala-aii infusin, shwing a highly significant crrelatin. The line intercepts the zer-change pint n the y-axis at a plasma renin activity f 5.7 ng All ml hur'', almst exactly the mean nrmal value (5.6 ng/ml hur''). Circulatin Research, Vl. 37, Nuember nrmal plasma renin activity wuld nt shw a fall in bld pressure with l-sar-8-ala-aii infusin, as suggested in Figure 1. In cntrast, there was n statistically significant crrelatin between the rats' bld pressures, assessed as the base-line bld pressure recrded directly n the day f the experiment, and their plasma renin activities (Fig. 5) (r = 0.42, P > 0.05). In five rats, the l-sar-8-ala-aii infusin rate was increased t 10 jtg/min near the end f the infusin. Nne f these rats shwed an additinal fall in bld pressure r any fall at all if the 4-^g/min infusin rate had had n effect. These results indicate that 4 /ig/min represented a maximal dse and suggest that differences in the bld pressure respnse were nt due t differences in the effective infusin rates frm rat t rat. This finding is in keeping with the bservatin f ttal blckade f the pressr effect f All with 4 /xg l-sar-8-ala-aii/ min. In the sham-clipped grup (N = 9), the maximum bld pressure fall was 15 mm Hg, bserved during tw separate l-sar-8-ala-aii infusins in a

5 644 MACDONALO. BOYD. PEART Plasma Renin Activity (ngai/ml/hr) 50- IDr-0.42 p ij ' 160 ' Initial Mean B.P. (mm Hg) FIGURE 5 Crrelatin between plasma renin activity and initial (baseline) mean bld pressure (B.P.). The crrelatin falls utside the 95% cnfidence limits. rat with a nrmal plasma renin activity f 4.4 ng/ml hur" 1. Only ne ther rat shwed a fall (5 mm Hg). Of the ther seven rats, five shwed n fall and tw shwed transient rises f 3 and 5 mm Hg, respectively. In five sham-clipped rats, a left nephrectmy was perfrmed as it was in the hypertensive grup. Three f these rats shwed n detectable fall in bld pressure, ne shwed a 2-mm Hg decrease, and the fifth (whse bld pressure had fallen by 5 mm Hg during l-sar-8- Ala-AII infusin) shwed a similar 5 mm Hg fall fllwing nephrectmy. Statistically, the shamclipped grup shwed n significant fall in bld pressure with either angitensin blckade r left nephrectmy. Discussin The extent f invlvement f the renin-angitensin system in all types f renal hypertensin is unsettled. Recent attentin has fcused n the tw-kidney type (unilateral renal ischemia r cnstrictin with the cntralateral kidney left untuched). Varius grups have presented data which suggest that this type f renal hypertensin represents a mdel f renin- and angitensindependent hypertensin based n studies with All blckers r antibdies (3, 4) r with inhibitrs f AI cnversin (9, 10). Such studies have nt been unanimus. Eide (11) failed t relieve tw-kidney hypertensin with active All immunizatin in the rat, and Pals and c-wrkers (2), althugh they were able t reduce tw-kidney hypertensin in the early (up t 2 weeks after inductin) phase using l-sar-8-ala-aii, failed t find any significant effect in mre chrnically hypertensive rats (5-6 weeks frm inductin). Bing and Nielsen (4) fund a variable effect using l-sar-8-ala-aii in cnscius and anesthetized twkidney hypertensive rats 1 and 4 mnths after clipping. It is true that plasma renin levels may be elevated in this frm f hypertensin (6, 12), but this phenmenn may be secndary t the hypertensin because f sdium lss frm the untuched kidney (6, 7). In many instances, hwever, plasma renin levels are within nrmal limits bth in man and experimental animals (13, 14), and much wrk has been dne n the physilgy f renal hypertensin and the pharmaclgy f renin and angitensin t shw hw this hrmne system might exert abnrmal physilgical effects in the presence f nrmal measured plasma renin levels. Varius neural mechanisms f secndary hypertensin fllwing initial inductin by renin and angitensin have been suggested (15). The pssibility that renin and angitensin levels, althugh within the nrmal range, are "inapprpriately" high fr the prevailing bdy sdium status r the prevailing angitensin receptr sensitivity (13, 16) has als been mentined. In the rats studied in the present series f experiments, the mean plasma renin activity f the hypertensive grup was significantly elevated (P < 0.01) cmpared with that f the sham-clipped grup. The hypertensive rats were readily divisible int thse with bld pressure declines during l-sar-8-ala-aii infusin f mre than 20 mm Hg and thse with lesser falls. Renin levels shwed an almst clear-cut difference, with rats with the larger declines having significantly higher plasma renin levels than rats with the smaller declines (P < 0.01). Fr the hypertensive grup as a whle, there was a strng crrelatin (r = 0.78, P < 0.01) between plasma renin activity and the bld pressure fall induced by l-sar-8-ala-aii. The susceptibility f the hypertensin t angitensin blckade suggests that renin and angitensin cntribute t the bld pressure elevatin. Hwever, ur data shw that this cntributin is n simple relatinship, since (1) the degree f hypertensin did nt crrelate significantly with the plasma renin levels (Fig. 5) and (2) althugh l-sar-8-ala-aii caused bld pressure falls in many rats, the levels reached were within the sham-clipped cntrl range in nly fur rats and the mean levels reached during angitensin blckade were significantly higher than the levels 24 hurs after nephrectmy even in thse rats with Circulatin Research, Vl. 37, Nvember 1975

6 1-Sar-8-Ala All AND RENAL ARTERY CLIP HYPERTENSION 645 majr (> 20 mm Hg) l-sar-8-ala-aii-induced declines (Fig. 3). Similar findings have been reprted by Bing and Nielsen using l-sar-8-ala-aii (4) and by Bumpus and his clleagues (17) using a slightly different angitensin blcker. The strng crrelatin between plasma renin activity and the fall in bld pressure with l-sar-8- Ala-AII suggests that in these rats the dependence f the hypertensin n renin and angitensin is clsely related t the degree f elevatin f plasma renin activity. Pals and Masucci (18) have reprted a similar relatinship between plasma renin activity and the depressr effect f l-sar-8-ala-aii in cnscius dgs with different types f hypertensin, including chrnic malignant ne-kidney r acute tw-kidney hypertensin. If renin levels were fr any reasn inapprpriately high in the nrmalrenin grup, their hypertensin shuld still have been susceptible t angitensin blckade. In ur series f experiments it was nt. It may be inferred that in this nrmal-renin grup, renin and angitensin are nt imprtant factrs in the maintenance f the hypertensin. Gavras et al. (16) have shwn that sdium depletin can change the status f nrmal and ne-kidney hypertensive rats, usually unrespnsive t angitensin blckade, s that bld pressure falls similar t thse previusly described in twkidney hypertensin ccur (3). They have prpsed that sdium depletin reveals a dependence f bld pressure n renin and angitensin which exists even when l-sar-8-ala-aii is ineffective. Our data are cnsistent with their experimental findings, since renin levels in salt-depleted rats are sure t be elevated, althugh these data were nt presented by Gavras et al. (16). The rats wuld therefre fall int the grup whse bld pressures we wuld expect t fall (Fig. 1). Rather than revealing an inherent dependence n renin and angitensin, hwever, we think that the elevated renin levels represent an increased quantitative cntributin t bld pressure maintenance regardless f the cntemprary bld pressure. In this case, angitensin blckade is predictably successful in reducing bld pressure. The distinctin t be made, therefre, is nt between ne-kidney and tw-kidney hypertensin but between highrenin and lw-renin hypertensin. If, in severe hypertensin, sdium lss leads t elevated plasma renin levels (10), the hypertensin will t sme extent be dependent n renin and will be susceptible t angitensin blckade, withut renin and angitensin being the initial causal factrs in the elevatin f bld pressure. The Circulatin Research, Vl. 37, Nvember 1975 failure f l-sar-8-ala-aii-respnsive rats t achieve bld pressures within the nrmal range (assessed by the sham-clipped rats' bld pressure range and by bld pressures reached in the hypertensive grup 24 hurs after left nephrectmy) further suggests that, even when renin and angitensin are implicated, they cannt accunt fully fr the bld pressure elevatin. It might be pstulated that these experiments have nt cvered the pssibility that All exerts effects n a prlnged time curse which are nt altered by the infusin f an inhibitr fr 2 hurs r less. This situatin wuld include the effects f aldsterne. It has been shwn, hwever, that in hypertensin induced in rabbits by All infusin ver several mnths (102 days), cessatin f infusin results in a fall t nrmal levels r belw within as shrt a perid as 2 minutes (19). Such a thery wuld als require that angitensin induce these secndary mechanisms in inverse relatinship t its plasma level, since they are apparently absent when renin levels are high and angitensin blckade acts t reduce bld pressure. Other factrs which might have influenced the respnse t l-sar-8-ala-aii were als studied. Hwever, the severity f renal impairment (bld urea), the changing dependence n renin and angitensin (time since clipping), and the initial bld pressure did nt appear t influence the results f angitensin blckade. Bing and Nielsen (4) have pstulated that a failure t reduce bld pressure with l-sar-8-ala- AII may be related t an inherent pressr respnse t the drug which they assessed by the pst-1- Sar-8-Ala-AII increase in bld pressure ver cntrl levels. In ur experience, such an increase was uncmmn and was nt evident frm the grup mean pstrecvery bld pressure. Neither was there any assciatin between the presence r the absence f a preliminary rise and the absence r the presence, respectively, f a subsequent fall in bld pressure. It is pssible that this rebund increase in bld pressure is due t an increase in renin release frm the kidneys induced by inhibitin f angitensin negative feedback by l-sar-8-ala-aii (4, 20). Such an increase in renin may have partially ppsed the depressr effect f l-sar-8-ala-aii. It is unlikely that this phenmenn is the basis fr the failure f many rats' bld pressures t fall in view f the highly effective blckade t a high dse f All infused during l-sar-8-ala-aii administratin, whether the analgue was assciated with a bld pressure fall r nt.

7 646 MACDONALD, BOYD. PEART Our data suggest that renin and angitensin cntribute t tw-kidney hypertensin when plasma renin levels are elevated, althugh, even then, the evidence indicates that they are nt the nly factrs invlved. With nrmal circulating renin levels, there is n evidence f a significant rle fr renin r angitensin n the basis f levels inapprpriately high in relatin t factrs such as sdium status r increased receptr sensitivity. Other factrs besides renin and angitensin therefre appear t be invlved in tw-kidney hypertensin. Their nature is unclear, but, since, withut exceptin, bld pressure falls t nrmal within 24 hurs f nephrectmy, ur findings are strngly in favr f their riginating in the kidney. Addendum Since the preparatin f this paper, tw relevant publicatins have appeared. Thurstn and Swales (Circ Res 35: , 1974) cmpared the effects f anti-angitensin serum administratin, l-sar-8-ala-aii infusin, and nephrectmy n bld pressure in the tw-kidney hypertensive rat. Since l-sar-8-ala-aii and nephrectmy reduced bld pressure and the antiserum did nt, they cncluded that renin may be active utside the circulatin in a site which is inaccessible t antiserum. Plasma renin values were nt measured, and the rats were anesthetized during the blcking experiments. Anther difference frm the present experiments is that individual data were nt given, even thugh individual variatins may be f great imprtance t a cmparisn f the effects f l-sar-8-ala-aii. The secnd paper is by Skulan and c-wrkers (Circ Res 35: , 1974). These authrs claim that sensitivity t renin and angitensin develps gradually after the applicatin f a renal artery clip in the tw-kidney mdel and that the renin levels in such animals fall n the dse-respnse curve f the pressr effects f hg renin infused under anesthesia int recently undipped animals. The data are presented as means ± SE. Individual variatins may be f great imprtance, since ne pssible way f recnciling these data with ur wn is t suggest that increasing plasma renin cncentratin in ur unanesthetized rats is assciated with increased renin respnsiveness, s that the ability f l-sar-8-ala-aii t lwer pressure still nly crrelates well with the plasma renin activity. Ackn wledg ment We are grateful fr the expert technical assistance f Ms. J. Smmers and Ms. S. Rddis. References 1. PALS DT, MASUCCI FD, SIPOS F, DENNING GS JR: Specific cmpetitive antagnist f the vascular actin f angitensin II. Circ Res 29: , PALS DT, MASUCCI FD, DENNING GS JR, SIPOS F, FESSLER DC: Rle f the pressr actin f angitensin II in experimental hypertensin. Circ Res 29: , BRUNNER HR, KIRSHMANN JD, SEALEY JE, LARAGH JH: Hypertensin f renal rigin: Evidence fr tw different mechanisms. Science 174: , BING J, NIELSEN K: Rle f the renin-system in nrm- and hypertensin. Acta Pathl Micrbil Scand [A] 81: , FRIEDMAN M, FREED SC: Micrphnic manmeter fr indirect determinatin f systlic bld pressure in the rat. Prc Sc Exp Bil Med 70: , GROSS F, DAUDA G, KAZDA S, KYNOL J, MOHRING J, ORTH H: Increased fluid turnver and the activity f the reninangitensin system under varius experimental cnditins. Circ Res 31(suppl II):II , BLAIR-WEST JR, COGHLAN JP, DENTON DA, ORCHARD E, SCOGGINS BA, WRIGHT RD: Renin-angitensin system and sdium balance in experimental renal hypertensin. Endcrinl 83: , BOYD GW, ADAMSON AR, FITZ AE, PEART WS: Radiimmunassay determinatin f plasma renin activity. Lancet 1: , MILLER ED JR, SAMUELS AI, HABER E, BARGER AC: Inhibitin f angitensin cnversin in experimental renvascular hypertensin. Science 177: , KRIEGER EM, SALGADO HC, ASSAN CJ, GREENE LLJ, FER- REIRA SH: Ptential screening test fr detectin f veractivity f renin-angitensin system. Lancet 1: , EIDE I: Renvascular hypertensin in rats immunized with angitensin II. Circ Res 30: , BIANCHI G, BALDOLI E, LUCCA R, BARBIN P: Pathgenesis f arterial hypertensin after the cnstrictin f the renal artery leaving the ppsite kidney intact bth in the anesthetized and in the cnscius dg. Clin Sci 42: , BIANCHI G, CAMPOLOL, VECETOA, PIETKAV, PIAZZA U: Value f plasma renin cncentratin per se, and in relatin t plasma and extracellular fluid vlume in diagnsis and prgnsis f human renvascular hypertensin. Clin Sci 39: , BOYD GW, JONES MBH, PEART WS: Radi-immunassay f angitensin II and plasma renin activity in human hypertensin. In Hypertensin '72, edited by J Genest and E Kiw. Berlin, Springer-Verlag, 1972, pp PAGE IH, BUMPUS FM (eds): Angitensin. Berlin, Springer-Verlag, GAVRAS H, BRUNNER HR, VAUGHAN ED, LARAGH JH: Angitensin-sdium interactin in bld pressure maintenance f renal hypertensive and nrmal rats. Science 180: , BUMPUS FM, SEN S, SMEBY RR, SWEET C, FERRARIO CM, KHOSLA MC: Use f angitensin antagnists in experimental hypertensin. Circ Res 32(suppl I):I , PALS DT, MASUCCI FD: Plasma renin and the antihypertensive effect f l-sar-8-ala-angitensin II. Eur J Pharmacl 23: , BROWN JJ, CHAPUIS G, ROBERTSON JIS: Effect f prlnged intravenus infusin f angitensin in the rabbit. Clin Sci 26: , VANDONGEN R, PEART WS, BOYD GW: Effect f angitensin II and its nn-pressr derivatives n renin secretin. Am J Physil 226: , 1974 Circulatin Research, Vl. 37, Nvember 1975