Regulation of bile secretion by sympathetic nerves in perfused rat liver

Although the biliary system is innervated by the autonomic nervous system, little is known about the regulation of bile secretion by hepatic nerves. In rat liver perfused in situ with constant pressure and erythrocyte-free medium, hepatic nerves were electrically stimulated (20 V, 20 Hz, 2 ms) by a platinum electrode placed around the hepatic artery and portal vein. Nerve stimulation caused a decrease in bile flow, bile acid secretion, and portal flow. The nerve effects on bile secretion were mediated via alpha 1-receptors. In this system, artificial reduction of perfusion flow by 30% led to a similar decrease of bile flow. In perfusion systems with constant flow and erythrocyte-free medium or with constant pressure and erythrocyte-containing medium, the nerve effects were reproduced despite the altered hemodynamics and the increased oxygen supply. In addition, partial inhibition by sodium nitroprusside of the nerve-induced reduction of portal flow had little effect on the reduction in bile secretion. In conclusion, a direct effect on bile formation was suggested. Yet an additional role of a vascular-mediated effect could not definitively be excluded. With the use of inhibitors of prostanoid synthesis the nerve effects on bile secretion were markedly reduced, suggesting a mediating or modulating role of prostanoids.