Pharmacological studies of gardenia fruit. V. Mechanisms of inhibitory effect of genipin on gastric acid secretion and its facilitatory effect on bile secretion in rats.

In the experiment on continuous perfusion of rat stomach in vivo, genipin inhibited only the gastric acid secretion induced by carbachol, but not by tetragastrin, or histamine. In the experiment on isolated organs, genipin showed a weak competitive anti-acetylcholine action on the intestinal contraction. Based on these facts and results reported previously, it is conceivable that anti-cholinergic action at least partly contributes to the genipin-induced inhibitory effect on gastric functions. Erythritol clearance was increased with the increase in bile flow by administration of genipin. Genipin showed a significant choleretic action, and just then the concentration of biliary bile acid was decreased inversely. In the relationship between bile flow and biliary bile acid excretion rate, the slope of regression line obtained from genipin-treated group was not significantly different from that of control, and these lines were approximately parallel to each other. Genipin did not affect the concentration of sodium, potassium, chloride, or bicarbonate in the bile collected during the initial stage, in which bile flow was increased, after administration. It is concluded from these results that genipin-induced choleretic action proceeds by a mechanism wherein water is driven along osmotic gradient which originates in the transport of bile acid-independent fraction from hepatocytes into canaliculi, mainly through active Na+ transport.