| Abstract: | Contractile responses were studied in isolated tubal segments of branches of the rat portal vein (luminal diameter approximately 300 microns) and hepatic artery (luminal diameter approximately 200 microns). Portal veins were approximately three times more sensitive to noradrenaline (NA) than hepatic arteries. 5-hydroxytryptamine contracted hepatic arteries concentration-dependently, whereas it produced only weak and inconsistent contractions in portal veins. Vasopressin effectively contracted hepatic arteries, whereas it had no effect on portal veins. Both vessel types responded to prostaglandin F2 alpha with contractions, although the drug potency was relatively low (EC50 greater than 10(-5) mol l-1). Histamine and carbachol failed to induce (hepatic arteries) or caused only weak (portal veins) contractions. Microsurgical hepatic hilar denervation reduced the catecholamine content of the parenchyma to less than or equal to 25% of controls. In both portal veins and hepatic arteries, the denervation procedure increased the NA sensitivity by factors of 3.1 and 2.0, respectively. In non-denervated livers, cocaine produced a similar increase of the NA sensitivity, whereas the drug had no significant effect in vessels from denervated animals. Thus, there was a marked difference between rat portal veins and hepatic arteries in their responsiveness to several contractile agents. Furthermore, the results of the present study indicate that the adrenergic nerves in both vessel types can be adequately removed by the microsurgical denervation procedure used. |
