EFFECT OF ADRENALECTOMY AND DEMEDULLATION OF THE ADRENALS ON VASOPRESSOR RESPONSES TO STIMULATION OF POSTJUNCTIONAL ALPHA-2-ADRENOCEPTORS

Abstract After adrenalectomy performed 18-12 h previously, the vasopressor responses induced by stimulation of postjunctional α 2 -adrenoceptors (agonist: B-HT 920) were attenuated in pithed normotensive rats in contrast to pressor responses mediated by postjunctional α 1 -adrenoceptors (agonist: cirazoline). Aldosterone and desoxycorticosterone both enhanced the vasopressor responses to the α 2 -adrenoceptor agonist B-HT 920 in adrenalectomized rats, but did not fully restore the effects. Demedullation of the adrenals also attenuated the vasoconstrictor processes evoked by stimulation of postjunctional α 2 -adrenoceptors 18–22 h later. This effect was reversed after an infusion with adrenaline. The combination of aldosterone and adrenaline produced full recovery of the increase in diastolic pressure elicited via α 2 -adrenoceptors in adrenalectomized (18–22 h) animals. The results suggest that circulating adrenaline and aldosterone (or corticosterone) are required for optimal functioning of vascular postjunctional α 2 -adrenoceptors.