Direct, concentration-dependent inhibition by taurocholate of pancreatic exocrine secretion and CCK release in conscious rats

Dynamics of the enterohepatic circulation of bile acids in healthy humans

Regulation of bile acid metabolism is normally discussed as the regulation of bile acid synthesis, which serves to compensate for intestinal loss in order to maintain a constant pool size. After a meal, bile acids start cycling in the enterohepatic circulation. Farnesoid X receptor-dependent ileal and hepatic processes lead to negative feedback inhibition of bile acid synthesis. When the intestinal bile acid flux decreases, the inhibition of synthesis is released. The degree of inhibition of synthesis and the mechanism and degree of activation are still unknown. Moreover, in humans, a biphasic diurnal expression pattern of bile acid synthesis has been documented, indicating maximal synthesis around 3 PM and 9 PM. Quantitative data on the hourly synthesis schedule as compensation for intestinal loss are lacking. In this review, we describe the classical view on bile acid metabolism and present alternative concepts that are based on the overlooked feature that bile acids transit through the enterohepatic circulation very rapidly. A daily profile of the cycling and total bile acid pool sizes and potential controlled and uncontrolled mechanisms for synthesis are predicted. It remains to be elucidated by which mechanism clock genes interact with the Farnesoid X receptor-controlled regulation of bile acid synthesis. This mechanism could become an attractive target to enhance bile acid synthesis at night, when cholesterol synthesis is high, thus lowering serum LDL-cholesterol.

Prolonged stimulation of pancreatic serous secretions by bile and sodium taurocholate in anaesthetized rats

There have been numerous reports that infusion of either natural bile or bile salts into the duodenum evokes a rapid increase in pancreatic secretion through the release of the hormone secretin from the duodenal mucosa. We have extended this observation by the demonstration of an additional late increase in secretion which persisted for many hours and have sought to identify the processes underlying this increase. In anaesthetised rats, infusion of 20 mM taurocholate into the duodenum caused a staircase-like increase in the weight of pancreatic secretion which extended over many hours during which, the HCO[Formula: see text] and protein output of the secretion showed only minimal changes. This effect was also reproduced with intra-duodenal infusion of natural bile which was inferred to act though its taurocholate content. Since the stimulatory action was also obtained with superfusion of taurocholate or natural bile onto the small intestine and by intravenous injection of taurocholate, it was concluded that taurocholate acted by being absorbed into the bloodstream and then by exerting a stimulatory action on the exocrine pancreas. This action was inhibited by puromycin (a protein synthesis inhibitor), by furosemide (a Na( + )/K( + )/2Cl(-) cotransporter inhibitor), though not by SITS (an inhibitor of Cl(-)/HCO[Formula: see text] exchange). The long lasting increase in pancreatic serous secretion would be consistent with the possible activation of gene transcription by taurocholate leading to increased activity of the Na( + )/K( + )/2Cl(-) cotransporter through which the acinar cells increased their secretions.

Mechanism of acute pancreatitis exacerbation by enteral bile-pancreatic juice exclusion

Using an original model, the donor rat model, we previously showed that bile-pancreatic juice exclusion from gut exacerbates ligation-induced acute pancreatitis. Here, we examine the mechanism by which bile-pancreatic juice exclusion from gut exacerbates acute pancreatitis. In the first part of the study we test the hypothesis that Na taurocholate and trypsin are components of bile-pancreatic juice that exacerbate acute pancreatitis when excluded. Our experiments show that combined replacement of Na taurocholate and trypsin ameliorates acute pancreatitis. In the second part of the study we test the hypothesis that bile-pancreatic juice exclusion from gut exacerbates acute pancreatitis via combined CCK-A and cholinergic receptor pathways. Our experiments show that combined CCK-A and cholinergic receptor blockade significantly ameliorates acute pancreatitis while blockade of either receptor alone does not. We conclude that bile-pancreatic juice exclusion-induced exacerbation of ligation-induced acute pancreatitis involves a neurohormonal duodenal response to exclusion of trypsin and Na taurocholate resulting in acinar cell hyperstimulation via combined CCK-A and cholinergic receptor-mediated pathways.