Alpha 1-adrenoceptor subtypes and the regulation of peripheral hemodynamics in the conscious rat

The peripheral hemodynamic effects of SZL-49, a prazosin analog capable of selectively inactivating the alpha 1a-adrenoceptor subtype, was evaluated in the conscious rat. One hour after SZL-49 administration, total peripheral vascular resistance and arterial blood pressure significantly decreased and cardiac output and heart rate increased. Twenty-four hours after SZL-49, blood pressure returned to control preinjection levels while peripheral resistance remained decreased and cardiac output and heart rate were elevated. The phenylephrine dose-response curves for mean arterial blood pressure and total peripheral vascular resistance were shifted to the right but the maximal responses were not decreased. These data show that the alpha 1a receptor plays a role in the tonic maintenance of arterial blood pressure. The alpha 1b receptor appears to participate in the response to exogenously administered agonists.