Fasting and postprandial hepatic bile flow in unanesthetized opossums.

In conscious opossums, we evaluated the relationship between hepatic bile flow and the intestinal motor function during fasting as well as after feeding. In six opossums, bipolar electrodes were implanted from the gastric antrum to the terminal ileum. After cholecystectomy, the common duct was ligated, and a catheter was tied into the proximal common duct for collecting hepatic bile. During subsequent studies, hepatic bile flow was measured, and bile was returned to the duodenum through an externalized duodenal catheter. Cyclic increases in bile flow during fasting did not show a close correlate with the duodenal migratory motor complex (MMC) cycle. Rather, bile flow showed peak values [0.11 +/- 0.02 (SE) ml/min] when phase III MMC activity reached the midileum. Hepatic bile flow correlated closely with the amount of bile acid secreted by the liver. When the bile acid pool was depleted by diverting bile from the intestine, hepatic secretion of bile fell to uniformly low values of approximately 0.04 ml/min that did not show cyclic variation. Hepatic bile flow after feeding increased to a maximal value of 0.12 +/- 0.01 ml/min at 90 min. We conclude that increases in hepatic bile flow during fasting and after meals are determined mainly by variations in intestinal motor activity that alter small bowel transit and thereby affect the enterohepatic circulation of bile acids.

Cl- secretion induced by bile salts. A study of the mechanism of action based on a cultured colonic epithelial cell line.

When applied to the basolateral (serosal) side of the T84 colonic epithelial monolayer, taurodeoxycholate caused net Cl- secretion in a dose-dependent manner with a threshold effect observed at 0.2 mM. In contrast, when applied to the apical (luminal) surface, concentrations of taurodeoxycholate below 1 mM had little or no effect. Only when the concentration of taurodeoxycholate present on the apical side was greater than or equal to 1 mM did apical addition results in an electrolyte transport effect. This apical effect on electrolyte transport was associated with an abrupt increase in the permeability of the monolayer. Cyclic AMP and cyclic GMP in the T84 monolayers were not increased by the bile salt, but in the presence of extracellular Ca2+, free cytosolic Ca2+ increased with a graded dose effect and time course that corresponded approximately to the changes in short circuit current (Isc). The results suggest that luminal bile salts at a relatively high concentration (greater than or equal to 1 mM) increase tight junction permeability. Once tight junction permeability increases, luminal bile salts could reach the basolateral membrane of the epithelial cells where they act to increase free cytosolic Ca2+ from extracellular sources. The resulting increases in free cytosolic Ca2+, rather than in cyclic nucleotides, appear to be involved in transcellular Cl- secretion.

Effects of oral laxatives on colonic motor complexes in dogs.

The effect of oral laxatives on the organisation of colonic motor complexes was investigated in four conscious dogs. Six strain gauge transducers were implanted on the colon of each dog. After a control period of two to three hours, dogs were orally dosed with 1, 2, or 4 ml/kg of castor oil, or 0.5 g/kg magnesium citrate. Oral olive oil, 4 ml/kg, was used as control. The recording was continued for another 10 hours or until defecation occurred. Each dog showed spontaneous cyclic bursts of contractions (contractile states) at all recording sites during the control period. Contractile states migrating orad or caudad over at least half the length of the colon were called colonic migrating motor complexes (CMMC). Castor oil and magnesium citrate significantly increased the period of colonic motor complexes, but olive oil had no significant effect. None of the above substances changed the percentage of orad migrating motor complexes, as compared with the control values. Periods in which colonic motor activity was completely absent for at least 60 min over at least three consecutive recording sites occurred more frequently after all of the substances. The occurrence of these periods of inhibition, however, was not a consistent feature and there seemed to be no relationship between the occurrence of inhibitory periods and defecation during the recording period. The dogs defecated within 10 hours after administration of magnesium citrate, 1, 2, and 4 ml/kg of castor oil in 12.5, 25, 37.5, and 88.8% of experiments respectively, but never with olive oil. Defecation was generally accompanied by giant migrating contractions in the colon. We conclude that oral laxatives, magnesium citrate and castor oil have a profound effect on colonic motor complexes and colonic motor activity. The period of CMMC is significantly prolonged after their oral administration because of an increased number of non-migrating motor complexes or periods of inhibition of motor activity.

Acid pH enhances the effects of taurodeoxycholate on water and solute transport in the human and rat jejunum.

The relative rate of unspecific binding of bile acids to brush border membrane vesicles resembles their relative potencies as intestinal secretagogues. This interaction of bile acids with brush border membranes is enhanced in an acid environment. We, therefore, studied the effects of taurodeoxycholate and taurocholate on water and solute transport at pH 7.6 and pH 4.0 in the human and rat jejunum. Five mM taurodeoxycholate induced significantly greater fluid secretion in the human jejunum at pH 4.0 than at pH 7.6 (p less than 0.02; n = 5), 10 mM taurocholate (n = 4) had no effect at either pH. In the rat 15 mM taurodeoxycholate at pH 4.0 induced greater fluid secretion (p less than 0.01; n = 6), released more phospholipid (p less than 0.001; n = 4) and enhanced absorption of mannitol more than at pH 7.6 (p less than 0.05; n = 6). In contrast fluid secretion and release of phospholipids induced by Triton X-100 were not affected by pH (n = 6), nor was fluid secretion induced by cholera toxin (n = 8). The data suggest that the enhancement of the secretory effect of taurodeoxycholate in an acid environment is due to its increased interaction with the mucosal surface, and support the concept that the ability of detergents to interact with the intestinal brush border membrane determines their effectiveness as intestinal secretagogues.

Effects of auranofin and myochrysine on intestinal transport and morphology in the rat.

Auranofin (SKF-D 39162) is an oral gold preparation for the treatment of rheumatoid arthritis. One of its major side effects is diarrhoea. To determine one possible mechanism for this we compared the effects of auranofin and myochrysine on intestinal water and solute transport in the rat. Jejunal perfusion with 2 mM auranofin (n = 5) induced fluid and electrolyte secretion and inhibited glucose absorption (p less than 0.01). Auranofin (0.2 mM) induced fluid secretion in the jejunum (n = 5; p less than 0.01) and colon (n = 6; p less than 0.01). In contrast, 2 mM myochrysine enhanced jejunal water and electrolyte absorption (n = 6; p less than 0.02). Both compounds enhanced absorption of mannitol (p less than 0.01). Perfusion of 0.2 mM auranofin for two hours had no significant effect on mucosal c-AMP levels (n = 4). After perfusion for two hours with 2 mM auranofin the jejunal mucosa showed severe injury by light and scanning electronmicroscopy while myochrysine had no apparent effect. The damage after perfusion with 0.2 mM auranofin for two hours was less severe. Auranofin was more rapidly absorbed than myochrysine (p less than 0.05). These effects provide an explanation for the diarrhoea associated with auranofin therapy.

Effects of taurodeoxycholate on in vivo water and solute transport in rat jejunum in absence and presence of calcium.

Bile acids and fatty acids enhance the permeability of brush-border membrane vesicles for calcium. It has been postulated that increased influx of calcium into the enterocyte might be responsible for the fluid secretion induced by dihydroxy bile acids and fatty acids. During in vivo perfusion studies of the rat jejunum, 15 mM taurodeoxycholate induced secretion of electrolytes and water (P less than 0.001), reduced glucose absorption (P less than 0.001), and enhanced the absorption of mannitol (P less than 0.0125) and calcium (P less than 0.001). Calcium absorption continued to be enhanced during perfusion of a CaCl2-containing solution following the perfusion with taurodeoxycholate (P less than 0.05). In view of the previously demonstrated enhanced permeability of the apical brush-border membrane in the presence of bile acids, it is very likely that some calcium enters the enterocyte along the steep concentration gradient in the presence of taurodeoxycholate. In spite of enhanced calcium absorption, 15 mM CaCl2 had no effect on control absorption rates or on fluid secretion induced by taurodeoxycholate. The data indicate that the effects of bile acids on intestinal transport are not mediated by an influx of calcium into the enterocyte.

Protection by dietary proteins against the effects of bile acids on rat jejunum and stomach.

Because bile acids bind to certain proteins we examined whether the effect of dihydroxy bile acids on jejunal water transport and gastric mucosal function could be blocked by the presence of protein. In the rat jejunum 2.5% bovine serum albumin blocked the secretion of water and electrolytes induced by 2 mM deoxycholate, whereas 5% ovalbumin, which does not bind bile acids, had no effect. Bovine serum albumin protected large unilamellar liposomes from damage by taurodeoxycholate and reduced the monomer concentration of taurodeoxycholate, whereas ovalbumin afforded no protection. In equilibrium dialysis studies whey protein and bovine serum albumin reduced the free taurodeoxycholate concentration (150 mM HCl enhanced this effect). In the rat stomach taurodeoxycholate (2.5 or 10 mM) in the presence of 150 mM HCl reduced potential difference and enhanced sodium secretion and hydrogen ion loss. These effects were reduced in the presence of whey protein. We conclude that proteins that bind bile acids have the potential to protect mucosal membranes from the adverse effects of bile acids.

Effects of sulfodeoxycholate on rat and rabbit small intestine.

To determine how sulfation alters the biological properties of dihydroxy bile acids, we compared the effects of 3-sulfodeoxycholate (SDC) and deoxycholate (DC) in the rat and rabbit intestine. While 5 mM DC induced water and electrolyte secretion and inhibited glucose absorption in the rat, SDC enhanced jejunal and ileal water and solute absorption. SDC had no effect in the rabbit ileum. In the rat jejunum DC caused mucosal injury and enhanced mucosal permeability while SDC had no effect. In vitro in the rabbit ileum, 10 mM SDC enhanced net sodium flux and decreased net residual flux, while 0.5 mM DC reduced net sodium flux and induced Cl- secretion. Both bile acids increased short-circuit current and potential difference and decreased tissue conductance. During reversed-phase, high-performance liquid chromatography SDC was more polar than DC. Sulfation reduced the ability of DC to destroy large unilamellar liposomes by a factor of 10. Thus, sulfation abolishes the effects of DC on the intestine by enhancing the polarity of this molecule. The enhancement of intestinal solute and water absorption by SDC requires further study.

Effects of amphotericin B and cholera toxin on intestinal transport in the rat. An in vivo model for the effects of dihydroxy bile acids and fatty acids on intestinal transport.

In vivo perfusion experiments were performed in the rat jejunum and colon to test the hypothesis that the changes in intestinal solute transport induced by dihydroxy bile acids and fatty acids are the result of the combined effects of fluid secretion and enhancement of mucosal permeability. The hypothesis predicts that absorption of organic solutes will be reduced in inverse relationship to the absorption rates under control conditions and that absorption of small, nonabsorbable solutes such as mannitol will be enhanced by these agents. Fluid secretion was induced either by administering cholera toxin or by increasing the osmolality of the perfusion solution to 365 mOsm/L. Permeability was enhanced by adding amphotericin B, 50 micrograms/ml, to the perfusion solutions. The isotonic perfusion solutions contained 11.2 mM glucose and 4 mM triethylene, tetraethylene, pentaethylene, and hexaethylene glycol or mannitol as probes of passive permeability. In the jejunum cholera toxin induced fluid and electrolyte secretion and reduced organic solute absorption to a small but significant degree (p less than 0.05). Amphotericin B alone enhanced absorption of organic solutes, water, and electrolytes (p less than 0.01). In the presence of fluid secretion induced by an osmotic load, only absorption of triethylene and pentaethylene glycol was reduced. Addition of amphotericin B after exposure to cholera toxin or to the hypertonic solutions resulted in a further significant reduction of absorption of glucose and ethylene glycols (p less than 0.05). The combination of amphotericin B and cholera toxin resulted in enhanced absorption of mannitol (p less than 0.02). Similarly, 5 mM deoxycholate enhanced jejunal absorption of mannitol (p less than 0.01) and reduced the absorption of glucose and the low-molecular-weight ethylene glycols (p less than 0.01). In the colon the administration of amphotericin B after the exposure to cholera toxin resulted in enhanced absorption of glucose (p less than 0.05) in spite of continuing fluid secretion. The combination of fluid secretion and enhancement of mucosal permeability, therefore, reproduced all in vivo effects of bile acids and fatty acids on intestinal transport of organic solutes.

Comparison of cholesterol and beta-sitosterol: effects on jejunal fluid secretion induced by oleate, and absorption from mixed micellar solutions.

Jejunal fluid secretion induced by perfusion with oleic acid can be reduced by the addition of cholesterol. The present study was performed to test the specificity of this effect by comparing the effects of cholesterol with that of a plant sterol, beta-sitosterol during perfusion of the jejunum in healthy volunteers. In addition, we compared the solubilities of cholesterol and beta-sitosterol in micellar solutions and their jejunal absorption rates. One millimolar beta-sitosterol was as effective as 1 mM cholesterol in reducing jejunal fluid secretion induced by 6 mM oleate (n = 7). In mixed micellar solutions consisting of 10 mM taurocholate and 6 mM oleate, solubility of beta-sitosterol is about one third of cholesterol solubility. When cholesterol was gradually replaced by beta-sitosterol in the incubation mixture, beta-sitosterol reduced cholesterol solubility to a greater extent than would be expected from an equimolar replacement of cholesterol by beta-sitosterol. Absorption of beta-sitosterol was limited by its solubility in mixed micellar solutions and both sterols were absorbed at equal rates as long as their solubility limits were not exceeded (n = 5).

Effects of lysophosphatidylcholine on jejunal water and solute transport in the rat in vivo.

The effects of lysophosphatidylcholine on jejunal water and solute transport were studied in vivo in the rat. Five mM lysophosphatidylcholine significantly reduced absorption of water, electrolytes and glucose (P less than 0.05) and 10 mM lysophosphatidylcholine induced net fluid secretion. The effects of 10 mM lysophosphatidylcholine were significantly reduced in the presence of 5 mM phosphatidylcholine (P less than 0.05) and 2 mM cholesterol (P less than 0.05). The fractional absorption of lysophosphatidylcholine decreased with increasing concentration of the detergent in the perfusion solution. Increasing concentrations of taurocholate in the perfusion solutions potentiated the effects of lysophosphatidylcholine (P less than 0.01), although 10 mM taurocholate by itself had no significant effect on intestinal water and electrolyte transport. The data establish that lysophosphatidylcholine, a zwitterionic detergent, affects intestinal transport in the same way as bile acids, fatty acids and synthetic cationic or nonionic detergents. By comparison with the response of the human jejunum to taurodeoxycholate, it is likely that lysophosphatidylcholine generated during the normal process of digestion has an effect on intestinal water and solute transport in man.

Hepatic free fatty acids in alcoholic liver disease and morbid obesity.

Alcoholic liver disease is characterized by the accumulation of fat and inflammatory changes in the liver. Because free fatty acids, the precursors of triglycerides, can damage biological membranes, accumulation of free fatty acids in the liver might be in part responsible for the functional and morphological changes seen in alcoholic liver disease. We, therefore, determined the hepatic lipid composition in biopsies from 31 patients with alcoholic liver disease, 18 patients with morbid obesity, and 5 patients without evidence of liver disease. Free fatty acids were found in all liver biopsies. Patients with morbid obesity or alcoholic liver disease had significantly higher fatty acid and triglyceride levels than did controls (p less than 0.01). Patients with alcoholic liver disease had significantly higher fatty acid levels than did patients with morbid obesity (p less than 0.05), while there was no difference in the triglyceride concentrations between these two groups. The distribution of the fatty acids in the free fatty acid fraction differed significantly from that in the triglyceride fraction indicating a preferential incorporation of unsaturated fatty acids into triglycerides. This difference in the distribution pattern was lost in patients with the most severe forms of alcoholic liver disease. The data are consistent with the hypothesis that accumulation of free fatty acids in patients with alcoholic liver disease may be responsible for or contribute to the observed functional and morphological damages.

Effect of cholera toxin on ileal water and solute transport after resection of the proximal small intestine in the rat.

Intestinal adaptation after extensive small bowel resection results in mucosal hypertrophy and an increased capacity of the remaining small intestine to absorb solutes and water. We tested the ability of the adapted rat ileum to respond to a secretory stimulus, cholera toxin. Six weeks after 50% jejunal resection (short gut) or sham operation water and solute transport were measured in a 16 cm segment of ileum before and after exposure to cholera toxin in a single pass in vivo perfusion system. During the control periods absorption of glucose, acetate and water per unit length of intestine was significantly greater in short gut animals (P less than 0.05 to 0.001). After exposure to cholera toxin absorption of glucose and acetate was significantly reduced in both groups (P less than 0.05 to 0.01). Sodium and chloride secretion and net change in water movement in response to cholera toxin were significantly greater (P less than 0.05 to 0.01) in short gut animals. Generally the differences between short gut and sham operation animals disappeared when the data were normalised for mucosal weight. Chloride secretion per gram mucosa was less in short gut animals (P less than 0.001). The data indicate that the adapted small bowel is not only capable of enhanced absorption but also of enhanced net secretion in response to cholera toxin. The changes reflect the increased number of enterocytes per unit length of intestine after intestinal adaptation.

Effect of glucose on jejunal water and solute absorption in the presence of glycodeoxycholate and oleate in man.

Jejunal perfusion studies were performed in 12 healthy volunteers to study the effects of 14 and 56 mM glucose on fluid secretion induced by 5 mM glycodeoxycholate on 7 mM oleate. Glucose enhanced water absorption under control conditions and reduced water secretion induced by glycodeoxycholate or oleate (P less than 0.01). As has been observed previously, glycodeoxycholate and oleate inhibited glucose absorption (P less than 0.001) and significant linear relationships existed between net water movement and glucose absorption. Glycodeoxycholate also reduced the absorption of 14 mM arabinose (P less than 0.05) and oleate reduced the absorption of 56 mM mannitol (P less than 0.05). Reduced solute absorption in the presence of glycodeoxycholate and oleate, therefore, cannot be attributed to an effect on active transport alone. The relationships between sodium transport and water absorption varied with the glucose concentration in the perfusion solutions. Similarly, the relationships between glucose absorption and sodium absorption varied with glucose concentration. The data suggest that a significant amount of glucose can be absorbed without concomitant absorption of sodium. The data indicate that glucose absorption can stimulate water absorption directly without the mediation of sodium and that water movement follows glucose at a rate which maintains isotonicity.

Cholesterol reduces the effects of dihydroxy bile acids and fatty acids on water and solute transport in the human jejunum.

Jejunal perfusion studies were performed in 16 healthy volunteers to test the hypothesis that intraluminal cholesterol can mitigate the fluid secretion induced by dihydroxy bile acids and fatty acids. Fluid secretion in the presence of 5 mM taurodeoxycholate was somewhat reduced by 4 mM mono-olein which was used for the solubilization of cholesterol. Addition of 0.8 mM cholesterol reduced fluid secretion further (P less than 0.05). Fluid secretion induced by 4 mM oleic acid was changed to net absorption in a linear fashion with increasing cholesterol concentration in the perfusion solutions. 1 mM cholesterol reduced fluid secretion induced by 6 mM oleic acid (P less than 0.005), but had no effect on fluid secretion induced by 6 mM linolenic acid. Glucose absorption was generally affected in a similar manner as water transport. In vitro, 1 mM cholesterol reduced monomer activity of 6 mM oleic acid to 72.3 +/- 0.9% of control and that of linolenic acid to 81.1 +/- 1.7% of control. Although statistically significant (P less than 0.001), the difference in the effects of cholesterol on monomer activities of the two fatty acids was rather small and it is unlikely that changes in monomer concentration of fatty acids and bile acids account for the protective effect of cholesterol. The in vivo observations point to a new physiological role for biliary cholesterol: the modification of the response of the small intestine to the effects of dihydroxy bile acids and fatty acids.

Clinical features and prognosis of severe chronic active liver disease (CALD) after corticosteroid-induced remission.

Disappearance of symptoms, resolution of most biochemical abnormalities, and histologic improvement to mild chronic inflammation were accomplished in 69 of 123 patients (56%) with severe chronic active liver disease treated with corticosteroids for up to 6.5 yr. Remission of at least 6 mo duration was possible in 35 of the 69 (51%) after discontinuation of therapy while others relapsed promptly and required retreatment. The likelihood of sustained remission was not predicted by initial clinical or biochemical features, although patients developing cirrhosis during treatment invariably relapsed. Subsequent courses of treatment after relapse were equally effective in again inducing remission, but the probability of another relapse increased after each successive therapy and was 86% after three treatments. Six of twenty-two patients (27%) followed for at least 4 yr after initial remission had three or more relapses. Although patients who relapsed were more likely to develop cirrhosis, manifestations of portal hypertension and immediate survival were not affected by relapse. Complete disappearance of all manifestations of active disease was possible in 12 of the patients entering remission (17%), but only patients without cirrhosis consistently sustained this improvement. We conclude that relapse after cessation of therapy frequently follows corticosteroid-induced remission of severe CALD, especially if cirrhosis develops, but does not jeopardize response to subsequent treatments or alter early prognosis.

Effect of lecithin on jejunal absorption of micellar lipids in man and on their monomer activity in vitro.

The effect of lecithin on jejunal absorption of fatty acids and octadecenoylglycerol was studied in healthy volunteers with a jejunal perfusion system which excluded pancreatic and biliary secretions from the test segment. Lecithin significantly reduced the absorption of oleic acid (P less than 0.05) and octadecenoylglycerol (P less than 0.01), while it had no effect on the absorption of ricinoleic acid. In vitro, lecithin reduced monomer activities of all three lipids; the changes were greater for oleic acid and octadecenoylglycerol than for ricinoleic acid (P less than 0.02). From these data it is concluded that lecithin reduces monomer activity of fatty acids in mixed micellar solutions and that it can thereby reduce the absorption rates of micellar lipids. Intact lecithin is not absorbed under these conditions. Maldigestion of lecithin in pancreatic insufficiency may, therefore, aggravate the steatorrhea observed in this condition.

Effect of taurine conjugated bile salts with and without lecithin on water and electrolyte transport in the canine gallbladder in vivo.

Because dihydroxy bile salts alter water and electrolyte transport in the intestine, we tested the effects of taurine conjugated bile salts on water and electrolyte transport in the canine gallbladder in vivo. 16.7 mM taurodeoxycholate or taurochenodeoxycholate completely abolished net absorption of water (P less than 0.01). 40 mM taurocholate significantly reduced net water absorption (P less than 0.05), whereas 16.7 mM taurocholate had no significant effect. Net movement of electrolytes was closely related to net water movement. Water and electrolyte absorption continued undisturbed when the gallbladders were exposed to 16.7 mM taurodeoxycholate together with 5.6 mM lecithin. Biliary lecithin, therefore, is important for the protection of the mucosa of the gallbladder from the potentially damaging effects of bile salts.