THE INFLUENCE OF TOTAL PORTO-SYSTEMIC SHUNTING ON THE NORADRENALINE RESPONSE AND ON THE CONTRACTILE EFFECTS OF VARIOUS VASOACTIVE AGENTS INSMALL RAT PORTAL VEINS AND HEPATIC ARTERIES

Contractile responses were studied in isolated tubal segments of branc hes of the rat portal vein (diameter 300 mu m) and hepatic artery (dia meter 200 mu m) 1, 3 and 6 weeks after total porto-systemic shunt oper ation (PCS). 5-Hydroxytryptamine contracted hepatic arteries concentra tion-dependently, whereas it produced only weak and inconsistent contr actions in portal veins. Vasopressin effectively contracted hepatic ar teries, but had no effect on portal veins. Both vessel types responded to prostaglandin F-2 alpha with contractions, although the drug poten cy was relatively low. The responses to these agents were not changed significantly in hepatic arteries or portal veins of PCS rats compared with controls at any of the postoperative time intervals. In both por tal veins and hepatic arteries noradrenaline produced contraction-depe ndent contractions, portal veins being 3 times more sensitive to norad renaline than hepatic arteries. PCS did not change the noradrenaline s ensitivity in hepatic arteries, whereas it increased the noradrenaline sensitivity in portal veins after 1, but not after 3 or 6 weeks. This effect was enhanced by cocaine, suggesting a partial sympathetic dene rvation of branches of the portal vein as well as a complete reinnerva tion within 3 weeks. Furthermore, the results of this study indicate n o influence in any vessel type on the response to several vasoactive a gents after depriving the liver of splanchnic venous blood.