Alpha 1-adrenoceptor desensitisation

The effects of intravenous infusion with phenylephrine on pressor responses to bolus doses of phenylephrine were examined in conscious rabbits. Four hours infusions failed to attenuate responses except in animals pretreated with phenoxybenzamine to eliminate the alpha 1-adrenoceptor reserve. However, the doses of phenylephrine required to attenuate responses were very large and were not well tolerated. Thus alpha 1-adrenoceptors in rabbit vascular smooth muscles are relatively resistant to in vivo agonist desensitisation compared to alpha 2- and beta-adrenoceptors.