Factors producing various responses to acetylcholine in dog hepatic circulation.

Effect of acetylcholine on hepatic circulation was investigated in 33 mongrel dogs. Mean arterial blood pressure, hepatic artery flow, portal vein pressure and portal vein flow were determined after laparotomy under nembutal anesthesia. In order to analyse the complicated responses in hepatic blood flows to 3 mug of acetylcholine hydrochloride, the peripheral resistance of each vascular system was observed in hypotensive dogs, in vascular obliteration dogs and in portal vein shunting dogs. Observation under a hypotensive condition produced by exsanguination revealed that hepatic artery resistance responded to decrease in hepatic artery pressure in different ways depending on whether the systemic blood pressure was above or below 90 mmHg. Experiments in which the hepatic artery or portal vein were obliterated disclosed that there was a certain regularity in the induction of resistance change in the non-injected one of the two hepatic vessels. The result of shunting the portal vein suggested that the complicated change above mentioned would be the expression of the overlapping two sequential responses. Since these results are difficult to explain merely by the direct response of vascular smooth muscle to acetycholine, the possibility that the hypothetical communication between the hepatic artery and portal vein might be a cholinergic system was discussed.