Cardiac Post-Junctional Alpha1- and Beta-Adrenoceptors: Effects of Chronic Chemical Sympathectomy with 6-Hydroxydopamine

Alpha 1- and beta-adrenoceptor responsiveness and binding have been examined in cardiac tissues removed from guinea-pigs pretreated with 6-hydroxydopamine (6-OHDA) for 3 weeks. Results were compared with control tissues from sham-injected animals. Chemical sympathectomy with 6-OHDA resulted in an increase in the sensitivity of postjunctional beta-adrenoceptor-mediated responses to isoprenaline. No such increase was observed for the alpha 1-adrenoceptor-mediated responses to methoxamine. The increase in beta-adrenergic responsiveness was accompanied by a significant (P less than 0.05) 52% increase in the number of [3H]-dihydroalprenolol binding sites with no change in binding affinity. [3H]-Prazosin binding was not affected by pretreatment with 6-OHDA. The results suggest that cardiac beta- but not alpha 1-adrenergic responsiveness is regulated by the sympathetic innervation.