Characterisation of the adrenoceptor mediating changes in cyclic adenosine 3'-5' monophosphate in chick cerebral hemispheres

Abstract

Noradrenaline, adrenaline, isoprenaline and salbutamol induced marked accumulations of cyclic AMP in incubated slices of chick cerebral hemispheres. Isoprenaline was both more potent and more powerful than adrenaline or noradrenaline and the increase in cyclic AMP elicited by the catecholamines was powerfully antagonized by the beta-adrenoceptor antagonist propranolol but not by the alphapadrenoceptor blocker phentolamine. The order of potency of the catecholamines isoprenaline greater than adrenaline greater than noradrenaline and the ability of the non-catechol salbutamol to stimulate cyclic AMP accumulation in chick cerebral slices suggests that the beta-adrenoceptro may resemble that found in the lung (beta2) rather than that in the heart (beta1). Propranolol proved to be a very potent antagonist of the cyclic AMP response induced by isoprenaline in vivo. Beta-adrenoceptor blockade was still evident 12 hrs after a single injection of the durg although only negligible amounts of 3H-propranolol could be detected in cerebral tissue after 2 hrs.