Pre-and postjunctional beta-adrenoceptor mediated effects on transmitter release and effector response in the isolated rat portal vein

Abstract

Pre- and postjunctional control mechanisms of the portal vein of spontaneously hypertensive rats (SHR) were characterized. Emphasis was placed on the influence of the presynaptic .beta.-adrenoceptor mediated mechanism for regulation of neuronal noradrenaline [norepinephrine] (NA) release (studied as 3H overflow) and its consequences for the contractile response under in vitro conditions. Isoprenaline increased, whereas dl-propranolol decreased the release of neuronal NA during transmural nerve stimulation, while effector responses remained unaltered. d-Propranolol and the .beta.-1 selective adrenoceptor antagonist, metoprolol, did not affect these 2 variables. The presynaptic .beta.-adrenoceptors in the rat portal vein are mainly of the .beta.-2 type and mediate facilitation of neuronal transmitter release and concomitant changes of the effector responses of this tissue are below the level of detection under the present experimental conditions.