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The effects of altered hepatic blood flow, of splanchnic and hepatic nerve stimulation, and of injecting epinephrine and vasopressin (Pitressin) were studied by perfusing canine livers in vitro. Controlled hepatic arterial perfusions demonstrated a linear relationship between arterial pressure and hepatic arterial inflow. It was found that increases of hepatic artery flow slightly increased portal vein pressure and vascular resistance of the portal vein, and that increases of portal vein flow slightly increased hepatic artery vascular resistance. Splanchnic nerve stimulation caused vasoconstriction of the hepatic artery, portal vein, and mesenteric vasculature. Hepatic nerve stimulation caused constriction of only the hepatic artery and portal vein vasculature. Similar results were obtained by the administration of epinephrine. Pitressin caused marked vasoconstriction of the mesenteric vasculature, vasodilatation of the portal vein vascular bed, and slightly increased hepatic artery vasomotor tone. It was noted that the rise in portal vein vasomotor tone with sympathetic stimulation was due in part to constriction of the "postjunctional" resistance.

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