Postsynaptic alpha 1- and alpha 2-adrenoceptors in the vascular system of the herring gull, Larus argentatus

The nature of the vascular alpha-adrenoceptors has been studied in the herring gull, Larus argentatus. In the anaesthetized herring gull, both phenylephrine and clonidine elicited dose-dependent increases in arterial blood pressure. The alpha 1-adrenoceptor antagonist prazosin was a better antagonist of phenylephrine than were the alpha 2-adrenoceptor antagonists yohimbine and rauwolscine. Yohimbine and rauwolscine were better antagonists of clonidine than was prazosin. The maximum response to phenylephrine, but not clonidine, was lower in reserpine-treated birds, indicating that phenylephrine in high doses liberates endogenous catecholamines, which contribute to the effect. It is concluded that the herring gull possesses postsynaptic, vascular alpha-adrenoceptors, of both the alpha 1- and alpha 2-subtypes, similar to those found in mammals.