ISOSMOTIC ABSORPTION OF FLUID FROM RAT JEJUNUM IN VITRO

Transcription

1 GASTROENTEROLOGY Copyright 1968 by The Williams & Wilkins Co. Vol. 54, No.3 Printed in U.S.A. SOSMOTC ABSORPTON OF FLUD FROM RAT JEJUNUM N VTRO J. S. LEE, PH.D. Department of Physiology, University of Minnesota, Minneapolis, Minnesota n most studies on intestinal absorption in which the disappearance of a given solute from the mucosal side or its appearance on the serosal side or in the blood has been determined, the effect of the simultaneous movement of water and other solutes has too often been disregarded. However, the close relationship between the absorption of solutes and water has long been known; the literature has been reviewed among others by Durbin et al. l n a previous report 2 it was shown that water and solutes are transported across at least a part of the rat intestinal wall of an in vitro preparation as a current of lymph via the lymphatics. The fluid transported is isosmotic with mucosal fluid, and thus the absorption of the total solutes and water by this route would be mutually dependent. The purpose of this investigation was a further attempt to elucidate the interrelationship between the absorption of water and solutes. The osmolarity and composition of the absorbed fluid as well as the water absorption were determined under various conditions. Experimental Procedure A modified Fisher and Parson's in vitro intestinal preparation' as described previously' Received December 27, Accepted October 24, Address requests for reprints to: Dr. J. S. Lee, Department of Physiology, University of Minnesota Medical School, Minneapolis, Minnesota This investigation was supported by Grant PHS AM from the National nstitute of Arthritis and Metabolic Diseases of the National nstitutes of Health. The author wishes to express his sincere gratitude to Drs. Eugene Grim and N. Lifson for critically reading the manuscript and to Miss Kathyryn Duncan and Mr. Robert Schanz for valuable technical assistance. 366 was used. A short segment (15 to 25 cm in length) of upper jejunum of rats (350 to 420 g) fasted for 18 to 24 hr was employed; its upper end commenced 5 cm from the ligament of Treitz, and its mesentery was cut away as completely as possible. The serosal side of the segment was bathed in liquid petrolatum. A large volume of mucosal fluid (100 ml) was circulated by a pumping system through the lumen at a of about 20 ml per min to ensure a practically constant composition over the absorption period, 30 min in most experiments. The mucosal fluid was bicarbonate-buffered salt solution containing (millimolar concentration per liter) : Na+, 142; Ct, 124; K+, 5.8; Ca++, 1.5; H 2PO.-, 0.34; Mg++, 1.2; SO.=, 1.2; HCO,-, 25.4; glucose, 27, and having an osmolarity of 300 milliosm. The solution was aed with 5% CO,-95% O2 n some experiments, N ac was partially replaced with other solutes. The intraluminal distention pressure was maintained at 20 mm Hg unless otherwise specified. The absorbed fluid dripped to the bottom of the warm oil chamber and was collected in a graduated tube; its volume was measured and its composition determined with respect to glucose, Na, K, C, and Ca. The collection of the absorbed fluid always began after an equilibration period of 10 min. A longer period of equilibration (20 to 30 min) yielded no appreciable difference in results. The osmolarity of the mucosal and absorbed fluids was determined. n an absorption period of 30 min, the composition of the mucosal fluid remained constant except for a slight decline in glucose concentration (less than 10%). The mean mucosal solute concentrations or the averages between the initial and final concentrations are used throughout this paper. n the presentation of results, the solute concentration ratio and osmolarity ratio are used. The concentration ratio of a solute is defined as CA:CJ, i.e., between its concentration in the absorbed fluid (C A ) and that in the mucosal fluid (C M ). The osmolarity ratio is similarly the ratio between the osmolar concentrations of the absorbed and mucosal fluids. The net solute absorption is expressed as micromolar concentration per centimeter (of loop length) per

2 March 1968 SOSMOTC ABSORPTON 367 hour and water absorption, as microliters per centimeter per hour. Chemical analysis. Glucose was determined by the glucose-oxidase method." Chloride was ana!yzed by the method of Shales and Shales ; N a and K, by flame photometer. Osmolarity was determined by the Mechrolab vapor pressure osmometer. The osmolarity of an aqueous solution containing g of NaC per liter was taken as 300 milliosm. Calcium was determined by the fluorescent method of Klass: Results Effect of mucosal fluid osmolarity. The osmolarity of the mucosal fluid was varied by changing its NaCl concentration. The results are presented in table 1. The water absorption decreased with increasing osmolarity of the mucosal fluid. Water absorption with hypotonic fluid (306 ".liters per cm per hr) was more than 5 times greater than that (58 ".liters per cm per hr) with about 1 % times isotonic fluid. The osmolarity of the absorbed fluid was approximately the same as that of the mucosal fluid (osmolarity ratio around 1), whether the latter was iso-, hypo-, or hypertonic. The osmolarity ratio with hypotonic fluid was slightly larger than 1 (1.10) and that with hypertonic fluid slightly less than 1 (0.97). This small difference could have been due to mixing of the absorbed fluid with the residual plasma or intracellular fluid during passage through the intestinal wall. The glucose concentration ratio (C A : em) increased with increasing osmolarity of the mucosal fluid, the ratio being 0.89, 1.49, and 1.80 for hypotonic (202 milliosm), isotonic (304), and hypertonic (507) fluids, respectively. The sodium concentration ratio was slightly greater than 1 (1.11) with hypotonic mucosal fluid and less than 1 with isotonic or hypertonic fluids. The concentration ratios of potassium and chloride were less than 1 under all circumstances. The calcium concentration ratio was very small (0.17) with hypotonic fluid but increased with increasing osmolarity of the mucosal fluid. The net absorption s of individual and total solutes are listed in table 2. When the mucosal fluid was hypertonic, the absorption of total solutes was slightly reduced. The absorption s of glucose, Na, K, and Cl were all reduced, but that of Ca did not change. The absorption s of the individual and total solutes from hypotonic mucosal fluid differed very little from those with isotonic mucosal fluid, except for that of K, which was 87% higher with hypotonic fluid. Effect of hypertonicity of mucosal fluid due to excess of various solutes. The results of the effect of hypertonicity of the mucosal fluid caused by adding about 200 milliosmoles per liter of various solutes to the hypotonic mucosal fluid (about 200 milliosmoles per liter) on solute concentration ratio and water absorption are presented in table 3. The solutes studied were N acl, mannitol, sucrose, and urea. Mucosal concentration TABLE 1. Effect of osmolarity of mucosal fluid on water absorption and solute concentration ratio a Solute concentration ratio (CA :CM) Osmolarity Na Cl Glucose Na K Cl Ca Osmolarity ratio Water absorption mil!iosm/liter mm/liter ",liters/ em/hr 202 (5) ± ll± ± ± ± ± ± (11) ± ± ± ±0.06 b 0.34± ± ± (5) ± ± ± ± ± ± ± (2) a Composition of mucosal fluid (millimolar concentration per liter): glucose, 27; K+, 5.8; Ca++, 1.5; H 2 P04-, 0.34; HCO a-, 25.4; Mg++, 1.2; 804 -, 1.2, with varying concentrations of Na+ and C1- as shown in table. Values are means ± SD. Numbers in parentheses indicate number of experiments. b Mean of seven experiments.

3 1 368 LEE Vol. 54, No.3 TABLE 2. Comparison of mean solute absorption s with mucosal fluid of different osmolarities a Mucosal osmolarity Water absorption Mean solute absorption s Glucose Na K C Ca Total solutes milliosm/liter ",liters/cm/hr p,m/cm/hr p,osm/cm/hr a Based on the data in table 1. TABLE 3. Effect of hypertonicity of mucosal fluid due to excess NaC, mannitol, sucrose, or urea on water absorption and solute concentration ratio a Mucosal concentration Osmolarity Na Cl Additional solute Solute concentration ratio (CA :CM) Glucose Na K Ca C Osmolarity ratio Water absorptiod milliosm/liter mm/liter p,liters/ cm/hr 202 (5) 95' 69 None 0.89± ±O.02 O. 82± ± ±0.1O 1.lO± ± (5) NaC 1.65± ± ± ± ± ± ± (9)b Sucrose 1.91±0.34 a 1.89± ± ± ± ± ±7 417 (23)b Mannitol 2.20± ± ± ± ± ± ±8 395 (6) Urea 1. 71± ± ± ± ± O1± ±51 a Mucosal fluid contained (millimolar concentration per liter): K+, 5.8; Ca++, 1.5; Mg++, 1.2; S04~. 1.2; H ap04-, 0.34; HCOa-, 25.4; glucose, 27, with varying concentrations of Na+ and Cl- and additional solutes as shown in the table. Values are means ± SD. Numbers in parentheses indicate number of experiments. b Absorption period, 1 hr; others, 30 min. a Four experiments. Glucose CA:C M was less than 1 (0.89) with the hypotonic mucosal fluid, but was much greater than 1 (1.65 to 2.20) with all hypertonic fluids regardless of the nature of the solutes or NaCl concentrations. This result indicates that it is the hypertonicity per se rather than excess Na or any specific solute, which increases the glucose CA:C M Na CA:C M was less than 1 with fluid hypertonic by excess NaCl. However, in the presence of mannitol, sucrose or urea, Na CA:C M became much greater than 1 (1.36 to 1.89). Potassium CA:C M was less than 1 (0.62 to 0.85) in all cases except with urea, in which it was about 1 (1.05). Calcium CA:CM was greater than 1 (1.28 to 2.05) with fluid hypertonic by excess mannitol or sucrose, but less than 1 with other fluids. Chloride CA:C M was less than 1 (0.56 to 0.65) in all cases. The osmolarity ratio between the absorbed and mucosal fluids was equal to 1 with all fluids, indicating no change of total solute concentration in the absorbed fluid from that in the mucosal fluid. The water absorption was decreased when mucosal fluid was hypertonic due to the excess of any kind of solutes, but most markedly in the presence of the poorly absorbed solutes, mannitol and sucrose. When excess urea was present in the mucosal fluid, the water absorption (147 ""liters per cm per hr) was slightly greater than that (118 ""liters per cm per hr) when excess N acl was present. Effect of glucose concentration at constant osmolarity. The glucose concentration in the mucosal fluid was varied from 11 to 118 mm and the osmolar concentration (about 300 milliosm) was maintained by adjusting NaCl concentration. The results

4 March 1968 SOSMOTC ABSORPTON 369 TABLE 4. Effect of glucose concentration on water absorption and solute concentration ratio" Mucosal concentrations Na Solute concentration ratio (CA :CM) Glucose C Osmolarity Glucose Na K C mm/liter milliosm/ liter Osmolarity 'ratio Water,absorption lliters/ em/ hr 11 (6) ± ± ± ± ± ±29 27 (11) ± ± ± ± ± ±31 55 (4) ± ± ± ± ± (5) ± ± ± ± ± ±1O " Mucosal fluid composition (millimolar concentration per liter): K+, 5.8; Ca++, 1.5; H 2 P0 4 -, 0.34; Mg++, 1.2; S04~' 1.2; HCO a-, 25.4, with varying concentrations of glucose, Na+, and Cl- as shown in the table. Values are means ± SD. Numbers in parentheses indicate number of experiments. are presented in table 4. There was no significant difference in water absorption s when glucose concentration was in the range of 11 to 27 mm. When glucose concentration was raised to 55 mm or higher, water absorption declined considerably. The osmolarity ratio between the absorbed and mucosal fluids was equal to 1 in all cases, indicating no change of total solute concentration in the absorbed fluid from that in the mucosal fluid. Potassium and Cl C A : C M were less than 1 and showed no correlation with glucose concentration. Glucose C A: C M decreased with increasing glucose concentration and the reverse was the case for Na CA:C M Glucose CA:C M was greater than 1 when glucose concentration was 11 to 27 mm, but less than 1 at higher concentrations. Sodium C A : C M was less than 1 at low glucose concentration but greater than 1 at higher concentrations. The inverse changes of sodium and glucose CA:C M must be related to the maintenance of isosmolarity between the absorbed and mucosal fluids. The net absorption s of Na and glucose are shown in table 5. n the range of 11 to 27 mm of glucose in the mucosal fluid, the glucose concentration in the absorbed fluid increased proportionally with the mucosal concentration. Since water absorption was about the same in both cases, the glucose absorption thus increased proportionally with the mucosal glucose concentration. When glucose concentration was increased to 55 mm or higher, however, there was no further ap- TABLE 5. Effect of glucose and N a concentrations in the mucosal fluid on mean net absorption s of glucose, Na, and water" Mucosal Mean absorbed Mean net coneen tra tiod fluid concentration absorption s Glucose Na Glucose Na Glucose Na Water mm/liter mm/liter lm/ cm/hr lliters/ cm/hr a Calculated from the data in table 4. preciable increase in glucose concentration in the absorbed fluid. Since there was a decrease in water absorption, glucose absorption was reduced as compared with that obtained when mucosal fluid contained 27 mm glucose. This is in agreement with the observations of others. 8-1o Since the Na concentration in the absorbed fluid varies rather slightly with increasing mucosal glucose concentration, the change of net Na absorption was parallel to that of water absorption. At glucose concentrations from 11 to 27 mm, both Na and water absorption did not change while glucose absorption increased by more than 100% (from 3.8 to 7.9 p,m per cm per hr). When glucose concentration was 55 mm or more, both Na and water absorption decreased considerably while glucose absorption was still maintained. Effect of intraluminal distention pressure. The results for the effect of distention

5 370 LEE Vol. 54, No.3 TABLE 6. Effect of distention pressure on water absorption and solute concentration ratio a Solute concentration ratio (GA: GM) Distention pressure Glucose Na K Ca Cl Osmolarity ratio Water absorption mmhg p.liters/ em/ hr 2 (9) ± ± ± ± ± ± ± (10) ± ± ± ± 0.05 b 0.62 ± 0.05 b 1.00 ± ± 1g e 5 (8) 1.25 ± O':'r" ± ± ± O.~~ 0.60 ± ± ± (11) ± ± ± ± ± ± ± (7) 1.35 ± ± o.me 0.74 ± 0.05 e 0.39 ± 0.05 e 0.58 ± O.01e 1.00 ± ± 25 a Mucosal fluid composition (millimolar concentration per liter): glucose, 27; N a+, 142; Cl-, 124; K+, 5.8; Ca++, 1.5; H 2 P0 4-, 0.34; Mg++, 1.2; S04-, 1.2; HCOg-, 25.4; osmolarity, 304 milliosm. Values are means ± SD. Numbers in parentheses indicate number of experiments. b Five experiments. e Four experiments. TABLE 7. Effect of distention pressure on mean water absorption and mean solute absorption u Disten- Solute absorption sian pressure Glucose Na K Ca Cl Total solute Water absorption absorption mmhg p.m/em/hr p.osm/ em/hr p.liters/ cm/hr u Calculated from the data in table 6. pressure on water absorption and composition of the absorbed fluid are presented in table 6. t can be seen that the water absorption was much greater at high distention pressures (20 to 45 mm Hg). There was, however, no significant difference in s at pressures from 2 to 5mmHg. The osmolarity ratio was equal to 1 at all distention pressures tested, indicating no change of osmolar concentrations in the absorbed fluid. At low distention pressure (2 to 3.5 mm Hg), Na and glucose CA:C M were fairly close to 1 but, at distention pressures at or above 5 mm Hg, glucose concentration ratio increased considerablv above 1 (1.25 to 1.49) and Na C A: C M 'decreased to slightly below 1 (0.94 to 0.97). The C A: C M of K, Ca, and Cl were below 1 and were not correlated with distention pressure. Since the osmolarity of the absorbed fluid 'was the same as that of the mucosal fluid, the total solute absorption increased proportionally with the increase of water absorption at higher distention pressures, but glucose absorption increased to a larger extent than ion absorption, because of the concomitant large increase of glucose concentration in the absorbed fluid. This is shown in table 7 on net absorption s of solutes and water at various pressures. For instance, when pressure was increased from 2 to 45 mm Hg, the increase of total solute absorption (93%) was about the same as that of water (95%) or of Na (91%), while the increase of glucose absorption was much greater (204%). Other ion absorption s also 'increased but to a lesser extent. Discussion The results of this investigation demonst that the absorbed fluid is always isosmotic with the mucosal fluid, regardless of the osmolarity (hypo-, iso-, or hypertonic) or composition of the mucosal fluid or the magnitude of intraluminal distention pressure. This is consistent with the previous observation 2 that lymph formed during water absorption in vitro was always isosmotic with the mucosal fluid. This type of coupling between water and solute absorption has also been seen in dog mucosal membrane,u With isotonic mucosal fluid, Gilman and Koelle l2 13 have observed the transported fluid across rat intestine in vitro to be isotonic. From the

6 March 1968 SOSMOTC ABSORPTON 371 linear relationship between the transport s of solutes and of water, many investigators have speculated that the transported fluid is isosmotic with the mucosal fluid. 1, 14, 15 Moreover, we have found under in vivo conditions that, when the mucosal fluid was hypotonic, intravascular hemolysis occurred. 16 This indicates that the absorbed fluid must be hypotonic. Therefore, it appears that the formation of an interstitial fluid approximately isosmotic with the mucosal fluid is involved in the absorption of water and solutes from intestine either in vivo or in vitro. With a similar experimental procedure, Diamond 17 observed in rabbit gall bladder that the absorbed fluid was isosmotic with the mucosal fluid within a large range of mucosal osmolarity. Based on the ratio between the transport s of Na and water from mucosal to serosal bathing medium, Whitlock and Wheeler 18 also reached the same conclusion that the transported fluid across gall bladder is isosmotic with the bathing fluid. The isosmotic absorption of fluid across the wall of gall bladder and of intestine seems to suggest the operation of similar mechanisms of fluid transport in these two systems. n gall bladder, active transport of solutes (mainly Na and Cl) with passive movement of water has been proposed as the primary process in fluid transport,17, 18 Curran 19 has recently discussed the mechanism of intestinal absorption of fluid and maintained that the weight of the present evidence indicates that water transport is secondary to active transport of solutes. The isosmotic absorption of fluid by the present in vitro intestinal preparation is consistent with this hypothesis, as are a number of other observations of this investigation. These are discussed below. Effect of osmolarity on water and solute absorption. t has long been established that water absorption decreases with.the increase of osmolarity of the luminal fluid and it is the basis for assigning a role to osmosis in water absorption from intestine. Parsons and Wingate,20 using an in vitro rat intestinal preparation with isotonic salt solution as the serosal bathing fluid, have also observed the decrease of water absorption with the increase of mucosal osmolarity. n the present investigation the serosal side was initially bathed in oil, but, after a few minutes, the absorbed fluid accumulated on the serosal surface; thus, during most of the absorption period, the serosal side was actually bathed in the absorbed fluid which was found to be isosmotic with the mucosal fluid. Although there was no osmotic difference between the fluid on both sides of intestine, water absorption decreased with the increase of osmolarity of the mucosal fluid. Furthermore, Fisher21 found no change in water absorption by a large favorable or adverse osmotic difference between both sides of intestine. These observations indicate that it is the osmolarity per se of the fluid present but not the osmotic difference between mucosal and serosal fluids that determines the water absorption under these conditions. The decrease of water absorption with the increase of mucosal osmolarity can be at least partly explained by the mechanism of isosmotic absorption of fluid due to active transport of solute. Since the absorbed fluid is nearly isosmotic with the mucosal fluid, the transport of the same amount of solutes would obligate less passive movement of water with increasing mucosal osmolarity. For example, with the increase of mucosal osmolarity, when total solute absorption decreased, a large percentage decrease in water absorption occurred because less water per unit solute is required for isotonicity than with less concentd fluids. With a different rat intestinal preparation, Parsons and Wingate 20 found no appreciable change in total solute absorption but a large reduction of water absorption with the increase of mucosal osmolarity. These findings demonst that, at higher osmolarity of the mucosal fluid, the epithelial transport work on solute is not appreciably altered but passive water movement is greatly reduced. Effect of excess organic solutes on ion concentration ratio. When mucosal fluid

7 372 LEE Vol. 54, No.3 contained 27 mm glucose as the only organic solute, Na concentration ratio approached 1 while other ion concentration ratios (K, Ca, and Cl) were considerably less than 1 under all circumstances. However, in the presence of excess organic solutes such as glucose, mannitol, sucrose, or urea, Na and Ca concentration ratios were significantly greater than 1 (tables 3 and 4). Potassium concentration ratio was somewhat greater than 1 only in the presence of urea. The effect of excess organic solutes in the mucosal fluid on the increase of ion concentration ratio may be explained by the mechanism of isosmotic absorption of fluid due to active transport of ions. When an organic solute (especially one of the poorly absorbable ones) is present in excessive amount in the mucosal fluid, its concentration in the absorbed fluid would be lower than that in the mucosal fluid. As shown in table 5, glucose concentration in the absorbed fluid was appreciably lower than that in the mucosal fluid when mucosal concentration was 55 mm or more. n the case of mannitol or sucrose, the concentration of these solutes in the absorbed fluid most probably is negligible. Therefore, in the presence of excess organic solutes in the mucosal fluid, the absorbed fluid must contain higher concentrations of ions to attain is osmolarity and thus ion concentration ratios must be increased above unity. n this case the actively transported ions become opposed by an adverse concentration gradient. This is probably the main cause of the decrease in ion transport and consequently the net water absorption. However, it is difficult to explain the effect of urea. As shown in table 3, in the presence of excess of urea, although Na was transported against a large concentration gradient (Na CA~: C M = 1.36), the water absorption was more than 6 times greater than that with sucrose or mannitol and was somewhat greater than that with NaCl. Net Na transport in the presence of urea (18.3 j-tm per cm per hr) approached that with excess N acl (21.2 j-tm per cm per hr). Then, the question arises why urea caused no appreciable change in water or Na transport. t should be pointed out that urea did exert some osmotic effect on water transport; otherwise the water absorption should be the same as that with hypotonic mucosal fluid. These observations seem to suggest that some unknown mechanisms might be involved in this instance. The concentration ratio of Cl was lower than 1 under all circumstances. Electroneutrality is undoubtedly maintained by the presence of large quantities of other negative ions, mainly bicarbonate and lactic acid, which have been reported to be greatly increased in the absorbed fluid of the similar in vitro intestinal preparations. 12, 13, 22 Moreover, an increase of concentration of any solute in the absorbed fluid regardless of mechanism would decrease the concentration of other solutes to maintain osmotic equilibrium and, consequently, their concentration ratios. Glucose concentration ratio. Glucose concentration ratio was increased under the following conditions. (a) Glucose concentration ratio was less than 1 at low distention pressure (2 mm Hg), but increased to above 1 at higher distention pressures. The mechanism of distention pressure on the increase of active glucose transport is difficult to explain. (b) With hypertonic mucosal fluid due to excess of either N acl or organic solutes (mannitol, sucrose, or urea), glucose concentration ratio was increased while water absorption was decreased (tables 1 and 3). The increase of glucose concentration ratio is apparently the result of decrease of water absorption with less or unchanged active glucose absorption. Relationship between absorption of N a and glucose. Although it is well established that Na may play an important role in the absorption of glucose from intestine,19 the absorption s of these two solutes were not closely correlated under certain conditions. As shown in table 5, when glucose concentration in the mucosal fluid increased from 11 to 118 mm, glucose absorption increased from 3.8 to 6.0 p.m per cm per hr (by 58%) while Na absorption decreased from 26.8 to 14.1

8 March 1968 SOSMOTC ABSORPTON 373 ftm per cm per hr (by 48%). Moreover, when distention pressure was increased from 2 to 45 mm Hg, glucose absorption increased by 204% but Na absorption increased only by 91% (table 7). Relationship between absorption of water and individual solutes. Since the absorbed fluid is always isosmotic with the mucosal fluid, the absorption of water and of total solutes is linearly related. This has also been found by others in the everted intestine 23 or in vivo. 24 However, the relationship between the absorption of a particular solute and water is not necessarily the same because the average concentration of the solute is not constant. Variability in this respect differed for individual solutes. Sodium, Cl, and K were fairly closely related to water absorption under all circumstances; that of glucose was markedly contingent on condition in addition to of water transport. Effect of distention pressure on water absorption. The increase of water absorption at high distention pressure (table 6) is a confirmation of the observations made on intestine in situ 25 or in yitro However, in dog mucosal membrane, Hakim et a1. 27 have been unable to demonst the effect of the hydrostatic pressure on the mucosal side of water transport. Since the composition of the absorbed fluid differs much from that of the mucosal fluid, intestinal absorption of fluid is certainly not a simple filtration. Based on the correlation between lymphatic pressure and intraluminal distention pressure during water absorption from rat intestine in vitro, it has been suggested that the distention pressure might play some role in water transport via the lymphatic system. 4 Whether distention pressure may exert some effect on the mucosal epithelial activity remains to be studied. Summary n an in vitro preparation of rat upper jejunum with serosal side bathed in liquid petrolatum, it was found that the absorbed fluid was always isosmotic with the mucosal fluid, whether the latter was iso-, hypo-, or hypertonic. The isosmotic absorption was independent of intraluminal distention pressure or the nature of solutes in the mucosal fluid. Water absorption decreased with the increase of osmolarity of the mucosal fluid, although the bathing fluids on both sides of intestine were isosmotic. The total solute absorption also decreased, but only slightly. Water absorption and total solute absorption increased with the increase of distention pressure. Glucose concentration ratio (concentration in the absorbed fluid: concentration in the mucosal fluid) was less than 1 with hypotonic mucosal fluid and greater than 1 with hypertonic fluid due to excess of either NaCl, mannitol, urea, or sucrose. With isotonic fluid, glucose concentration ratio was greater than 1 only when intraluminal distention pressure was above 3.5 mm Hg. Sodium concentration ratio was greater than 1 when excess organic solute (glucose, mannitol, sucrose, or urea) was present in the mucosal fluid. Calcium concentration ratio was greater than 1 with mucosal fluid hypertonic due to excess of mannitol or sucrose. REFERENCES 1. Durbin, R. P., P. F. Curran, and A. K. Solomon on and water transport in stomach and intestine. Advance. Bio. Med. Phys. 6: Lee, J. S Glucose, electrolytes and water transport from intestine in vitro, p n Abstracts of the Twenty-third nternational Congress of Physiological Science, Tokyo. 3. Fisher, R. B., and D. S. Parsons A preparation of surviving rat small intestine for the study of absorption. J. Physiol. (London) 110: Lee, J. S Role of mesenteric lymphatic system in water absorption from rat intestine in vitro. Amer. J. PhysioL 204: Huggett, A. S. G., and D. A. Nixon Enzymic determination of blood glucose. Biochem. J. 66: 12p. 6. Shales, 0., and S. S. Shales A simple and accu method for the determination

9 374 LEE Vol. 54, No.3 of chloride in biological fluids. J. Bio. Chem.140: Klass, C. S The use of indicator calcein and its fluorescence in a rapid ultramicro titration of serum calcium. Amer. J. Clin. Path. 37: Annegers, J. H ntestinal absorption of hexoses in the dog. Amer. J. Physiol. 206: Fisher, R. B., and D. S. Parsons Glucose movements across the wall of the rat small intestine. J. Physiol. (London) 119: Holdsworth, C. D., and A. M. Dawson The absorption of monosaccharides in man. Clin. Sci. 27: Hakim, A. A Water absorption by dog intestinal mucosa. Minnesota Med. 48: Gilman, A., and E. S. Koelle on transport in the gut. Circulation 21: Gilman, A., and E. S. Koelle Subst requirements for ion transport by rat intestine in vitro. Amer. J. Physiol. 199: Curran, P. F., and A. K. Solomon on and water fluxes in the ileum of rats. J. Gen. Physiol. 41: Wilson, T. H Fluid movement across the wall of the small intestine in vitro. Amer. J. Physiol. 187: Lee, J. S ntravascular hemolysis during water absorption from small intestine. Amer. J. Physio.178: Diamond, J. M The mechanism of isotonic water transport. J. Gen. Physiol. 48: Whitlock, R. T., and H. O. Wheeler Coupled transport of solute and water across rabbit gall bladder epithelium. J. Clin. nvest. 43: Curran, P. F on transport in intestine and its coupling to other transport processes. Fed. Proc. 24: Parsons, D. S., and D. L. Wingate The effect of osmotic gradient on fluid transfer across rat intestine in vitro. Biochim. Biophys. Acta 46: Fisher, R. B The absorption of water and of some small solute molecules from the isolated small intestine of rat. J. Physiol. (London) 130: 651H) Wilson, T. H Concentration gradient of lactate, hydrogen and some other ions across the intestine in vitro. Biochem. J. 56: Barry, R. J. C., D. H. Smyth, and E. M. Wright Short-circuit current and solute transfer by rat jejunum. J. Physiol. (London) 181: McHardy, G. J. R., and D. S. Parsons Absorption of water and salt from the small intestine of the rat. Quart. J. Exp. Physiol. 42: Verzar, F Absorption from the intestine, p Longmans, Green and Co., New York. 26. Smyth, D. H., and C. B. Taylor Transfer of water and solutes by an in vitro intestinal preparation. J. Physiol. (London) 136: Hakim, A., R. G. Lester, and N. Lifson Absorption by an in vitro preparation of dog intestinal mucosa. J. Appl. Physiol. 18: