A. Chung

Bile acid stimulation of colonic adenylate cyclase and secretion in the rabbit

In vitro studies have suggested that the cyclic AMP system may be the mediator of bile acid-induced colonic secretion. The aims of our experiments were to quantify thein vivo effect of various doses of deoxycholic acid (DCA) on adenylate cyclase activity (AC) and net secretion in the rabbit colon. AC increased significantly (P<0.01) with each increasing concentration of DCA; at 8 mM the activity was 126±6 pmoles cAMP/mg protein/min, or 4 times the control. Phosphodiesterase activity (PDE) was affected and significantly decreased (P<0.01) only by 8 mM DCA. The volume of luminal fluid increased significantly (P<0.01) as a bicarbonate-rich solution with 4, 6, and 8 mM DCA in graded fashion. In conclusion, stimulation of a colonic mucosal cAMP system is strongly implicated as mediating DCA-induced colonic secretion.

Treatment of Gallstones with Chenodeoxycholic Acid and Phenobarbital

In a controlled trial, 36 patients with asymptomatic radiolucent gallstones were treated with chenodeoxycholic acid, 750 mg per day, phenobarbital, 180 mg per day, combination of both drugs, and placebo. After one year, chenodeoxycholic acid, phenobarbital and the combination, but not placebo, significantly decreased biliary cholesterol saturation. The effect was significantly greater with chenodeoxycholic acid and the combination than with phenobarbital. Gallstones size decreased more than 50 per cent in nine of 20 patients receiving chenodeoxycholic acid, either alone or combined with phenobarbital, but in no patient receiving only phenobarbital or placebo. Gallstones disappeared completely in tow patients. Abnormalities in liver-function tests in thriee of 36 patients and in five of 16 liver biopsies, occured with equal frequency in the four treatment groups. Thus, after one year, phenobarbital alone was ineffective in gallstone dissolution. Chenodeoxycholic acid alone or combined with phenobarbital, however, offered a partially effective and safe treatment for asymptomatic radiolucent gallstones.

PROPRANOLOL INHIBITS ADENYLATE CYCLASE AND SECRETION STIMULATED BY DEOXYCHOLIC ACID IN THE RABBIT COLON

Bile acids cause diarrhea by inducing colonic secretion, probably mediated through the cyclic AMP system. The aim was to determine the effects of an adenylate cyclase inhibitor, propranolol, on deoxycholic acid (DCA) stimulation of net secretion and the cyclic AMP system in the colon. In each of 30 New Zealand white rabbits, 0.9% NaC1 as control and 6 mM and 8 mM DCA were injected in random sequence into three colonic loops in situ. Propranolol, 4 mg per kg was administered intravenously to 12 of the 30 rabbits 1/2 hr before preparation of the loops, i.e., 5 1/2 hr before the rabbits were killed. In the 18 untreated animals, 6 and 8 mM DCA significantly stimulated colonic net secretion and mucosal adenylate cyclase activity; 6 mM DCA caused no change in mucosal phosphodiesterase activity, whereas 8 mM DCA caused a 25% decrease (P less than 0.01). In propranolol-treated animals compared to untreated animals, the volume of luminal fluid in controls was not different, with 6 mM DCA it was 88% less (P less than 0.01), and with 8 mM DCA it was 45% less (P less than 0.01); adenylate cyclase activity in controls was 43% less (P less than 0.01), with 6 mM DCA it was 67% less (P less than 0.01), and with 8 mM DCA it was 65% less (P less than 0.01); phosphodiesterase activity in controls and with 6 mM DCA was not different and with 8 mM DCA it was 38% greater (P less than 0.02). In conclusion, propranolol prevented DCA stimulation of colonic net secretion and inhibited the cyclic AMP system. Propranolol, therefore, warrants investigation as therapy for diarrhea caused by bile acids in the colon.

Effect of Propranolol on Bile Acid- and Cholera Enterotoxin-Stimulated cAMP and Secretion in Rabbit Intestine

Stimulation of net secretion by deoxycholic acid (DCA) in the colon and by cholera enterotoxin (CE) in the jejunum is mediated by cAMP. Propranolol (Pr) inhibits adenylate cyclase (AC) activity and net secretion induced by bile acid in the colon. The aim of this study was to assess the organ specificity of DCA and CE as well as the selectivity of Pr inhibition. Three colonic and three jejunal loops were prepared in each of 8 rabbits treated intravenously with Pr, 4 mg per kg, 1/2 hr before loop construction and in each of 10 untreated control rabbits. One milliliter of DCA, 6 mM, CE, 10 mug per ml, or heat-inactivated CE or 0.9% NaCl, as basal controls were injected in random order into each of the loops. The volume of luminal fluid and mucosal AC were measured in each intestinal loop 5 hr later. DCA in the colon stimulated AC 2-fold (P less than 0.01) and luminal fluid 15-fold (P less than 0.01). CE in the jejunum stimulated AC 2.3-fold (P less than 0.01) and luminal fluid 9-fold (P less that 0.01). No significant effects on volume or AC occurred in response to CE in the colon or to DCA in the jejunum. Pr pretreatment completely prevented the stimulation of AC and luminal fluid by DCA in the colon but did not affect the action of CE in the jejunum of the same animals. Thus, DCA and CE are organ-specific stimulants of cAMP systems, and Pr is a selective inhibitor of certain inducers of cAMP and net secretion.

Estrogen Enhances Dietary Cholesterol Induction of Saturated Bile in the Hamster

The influence of ethinyl estradiol (EE) on the effects of dietary cholesterol on the biliary saturation index and on the rate-limiting hepatic enzymes of cholesterol synthesis, hydroxymethylglutaryl-CoA-reductase, and bile acid synthesis, 7 alpha-hydroxylase, were determined. Four groups of 12 male hamsters were treated for 1 month with EE, 15 micrograms per kg per day, or placebo vehicle administered intraperitoneally and fed either a standard diet, 0.8 mg of cholesterol per g of food, or high cholesterol diet, 2.4 mg of cholesterol per g. The high cholesterol diet increased the saturation index to 1.00 +/- 0.03 (P less than 0.01) from 0.65 +/- 0.02 in untreated hamsters on the standard diet. EE treatment on the high cholesterol diet further increased (P less than 0.01) the saturation index to 1.15 +/- 0.02. The high cholesterol diet decreased (P less than 0.01) hydroxymethylglutaryl-CoA-reductase activity from 308 +/- 16 pmoles per mg per min in untreated hamsters on the standard diet. The addition of EE treatment had no effect on hydroxymethylglutaryl-CoA-reductase activity. The high cholesterol diet increased (P less than 0.01) 7 alpha-hydroxylase activity from 23 +/- 1.0 pmoles per mg per min in untreated hamsters on the standard diet. The addition of EE decreased (P less than 0.01) 7 alpha-hydroxylase activity from that in untreated hamsters on the standard diet. The conclusions are as follows: (1) EE prevented dietary cholesterol-induced stimulation of cholesterol 7 alpha-hydroxylase activity; (2) EE enhanced the ability of dietary cholesterol to induce saturated bile; and (3) gallstone formation in estrogen-treated women may result from impaired metabolism of dietary cholesterol.

Gallstone prevalence and biliary lipid composition in inflammatory bowel disease.

Biliary cholesterol saturation has been correlated with disease variables that might effect bile acid loss in ileitis patients with (N=9) or without (N=8) intestinal resection having a defined prevalence of gallstones. In addition, cholesterol saturation was determined in ulcerative colitis patients (N=7) and gallstone patients (N=18) as well as in 5 normal controls. Biliary cholestrol saturation in ileitis patients both with and without resection was similar to that in gallstone patients yet the prevalence of gallstones was only 12%. Cholesterol saturation did not correlate with ileal resection nor the extent, duration, or activity of ileitis. Biliary cholesterol saturation was not different in ulcerative colitis patients from that in normal subjects. It is concluded that cholesterol saturation of bile alone does not account for the high prevalence of cholesterol gallstones that has been reported in ileitis patients.

Inhibition by Propranolol of Bile Acid Stimulation of Rabbit Colonic Adenylate Cyclase in Vitro

UNLABELLED Bile acids, especially unconjugated deoxycholic acid, cause diarrhea by inducing colonic mucosal secretion of water and electrolytes. This effect has been shown to be mediated by adenylate cyclase (AC). Propranolol, a beta-adrenergic blocking agent which inhibits AC, may then prevent this action of bile acids on colonic mucosa. The aim of this study was to determine the effect of bile acids, catecholamines, and propranolol on AC activity in colonic mucosa. The in vitro effects of deoxycholic acid, taurocholic acid, NaF, epinephrine, norepinephrine, and propranolol on AC in rabbit colonic mucosa were determined. NaF, 10(-4) M, increased AC activity to 220% of control (P less than 0.01). Deoxycholic acid, 10(-4) M, increased AC activity to 178% of control (P less than 0.01). Lesser but significant (P less than 0.01) stimulation of AC occurred at both higher and lower concentrations of deoxycholic acid, with no effect at 10(-10) M. Taurocholic acid, 10(-4) M, and epinephrine and norepinephrine, 10(-2) M, 10(-4) M, 10(-6) M, and 10(-8) M, had no effect on AC. Propranolol, 10(-6) M, caused a 60% decrease (P less than 0.01) in the stimulated AC activity induced by 10(-4) M deoxycholic acid. Propranolol, 10(-4) M, decreased basal AC by 30% (P less than 0.01). IN CONCLUSION (1) Deoxycholic acid, but not taurocholic acid, epinephrine, or norepinephrine, stimulates colonic AC activity. (2) Propranolol inhibited this deoxycholic acid stimulation of AC. (3) Catecholamines are not intermediaries in this action of propranolol on colonic mucosal AC activity.

Feasibility of low-dose and intermittent chenodeoxycholic acid therapy of gallstones.

Chenodeoxycholic acid, by reducing the concentration of biliary cholesterol relative to that of bile acid and phospholipid, dissolves cholesterol gallstones. This bile acid, however, has potential dose-related hepatotoxicity and causes dose-related diarrhea. Therefore, the feasibility of low-dose and intermittent therapy was assessed by studying the induction and persistence of chenodeoxycholic acid-induced biliary lipid changes. Biliary lipid composition with each of 3 doses of chenodeoxycholic acid was determined in bile samples obtained by cholecystokinin-stimulated duodenal drainage before, after one week and one month of treatment, and up to 9 weeks after discontinuation of treatment. The lowest dose that significantly reduced the relative concentration of biliary cholesterol was 250 mg/day. A significant reduction occurred one week after initiation of treatment and was maintained for 9 weeks follwing discontinuation of treatment. Thus, clinical trials of low-dose and intermittent chenodeoxycholic acid therapy for gallstone prophylaxis or dissolution are warranted.

DIETARY CHOLESTEROL AFFECTS CHENODEOXYCHOLIC ACID ACTION ON BILIARY LIPIDS

Chenodeoxycholic acid (CDC) decreases biliary saturation and dissolves gallstones in one-half of the treated patients. Dietary cholesterol also affects biliary lipids and is a possible factor explaining unsuccessful CDC therapy. The aim of this investigation was to study the effect of high and low dietary cholesterol on the CDC-induced decrease of biliary saturation and activity of hepatic hydroxymethylglutaryl coenzyme A reductase (HMG-CoAR). Seventy two hamsters in six groups were fed for 1 month one of three diets: 0.8 mg of cholesterol per g of food, 2.4 mg of cholesterol per g, or cholesterol-free. On each diet hamsters received no CDC or CDC 30 mg per kg per day. When animals were killed, biliary lipids were determined and the activity of hepatic HMG-CoAR was assayed. CDC administration decreased the saturation index (SI)(P less than 0.01) in hamsters on the high cholesterol and standard diets but not on the cholesterol-free diet. The SI in CDC-treated hamsters on the high cholesterol (0.78 +/- 0.03) and cholesterol-free (0.68 +/- 0.02) diets were greater (P less than 0.02) than in CDC-treated hamsters on the standard diet (0.48 +/- 0.03). CDC decreased (P less than 0.01) HMG-CoA reductase activity on each diet. In comparison to HMG-CoAR activity (190 +/- 7.6 pmoles per mg per min) in CDC-treated hamsters on the standard diet, the activity in CDC-treated hamsters on the high cholesterol diet (176 +/- 5.8 pmoles per mg per min) was decreased ( less than 0.05), whereas the activity on the cholesterol-free diet (495 +/- 11.5 pmoles per mg per min) was greater (P less than 0.01). It is concluded that: (1) dietary cholesterol is necessary for optimum CDC inhibition of HMG-CoAR; (2) high cholesterol and cholesterol-free diets prevent maximum CDC decrease of the biliary saturation index; (3) dietary cholesterol alterations may therefore be one cause of the failure of CDC dissolution of gallstones.