Desensitization of vascular and platelet alpha 2-adrenoceptors in rabbits with perinephritis hypertension.

The effects of infusion of alpha-adrenoceptor agonists on blood pressure, pressor responses to bolus doses of agonists and to platelet aggregation were examined in rabbits with perinephritis hypertension and in sham-operated controls. Pressor responses to bolus doses and infusions of phenylephrine, an alpha 1-selective agonist, were greater in hypertensive rabbits. In contrast, responses to boluses but not infusions of alpha-methylnoradrenaline, a selective alpha 2-agonist, were increased in hypertensives. During alpha-methylnoradrenaline infusions pressor responses to bolus doses of alpha-methylnoradrenaline and the aggregatory response of platelets to adrenaline were attenuated in all rabbits, consistent with alpha 2-adrenoceptor desensitization. Attenuation and recovery were observed within minutes of commencing and ceasing infusion. The extent of attenuation and rate of change were generally increased in hypertensive animals. This could explain the apparent increase in pressor responses to bolus doses but not infusions of alpha-methylnoradrenaline in the hypertensive rabbits. It might also contribute to the lability in blood pressure observed in these animals.