Endothelin-1 causes vasoconstriction and vasodilation in the blood perfused liver of the dog

Endothelin-1 (ET-1; 1 pmol-1 nmol) was injected intra-arterially into the canine hepatic artery perfused, in situ, with arterial blood. The characteristic arterial vascular response to ET-1 was biphasic consisting of an initial increase in flow (vasodilatation) of short duration followed by a prolonged reduction in flow (vasoconstriction). The hepatic portal circuit was perfused at a constant flow with blood derived from the mesenteric circuit. Hepatic portal inflow pressure was continuously recorded. ET-1 injected intraportally increased the portal perfusion pressure indicating an increase in portal inflow resistance. This portal vasoconstrictor response to ET-1 was of much longer duration than that previously observed with other vasoactive agents in this vascular territory.