An interaction between prejunctional α-adrenoceptors and prejunctional β-adrenoceptors

Abstract

The ability of isoprenaline to enhance transmitter release from sympathetic nerves in rat atria incubated with [ 3H]noradrenaline was assessed under three conditions of prejunctional α-adrenoceptor activation: in the presence of phentolamine, in the presence of noradrenaline, and in the absence of either drug. Isoprenaline-induced enhancement of transmitter release was inversely related to the degree of activation of prejunctional α-adrenoceptors. Thus there appears to be an interaction between the prejunctional α-adrenoceptor inhibitory mechanism and the prejunctional β-adrenoceptor facilitatory mechanism. In rabbit ear arteries incubated with [ 3H]noradrenaline, isoprenaline facilitated transmitter release in the presence but not in the absence of phentolamine. Therefore in some tissues it may be necessary to block prejunctional α-adrenoceptors before prejunctional β-adrenoceptors can be demonstrated.