Alpha-adrenoceptor responses of an isolated human artery and blood pressure.

This cross-sectional study examined responses of the isolated cystic artery to 3 alpha-adrenoceptor agonists and the effects of 2 antagonists in relation to subjects' blood pressures. Potency of the 3 amines studied was: alpha-methylnorepinephrine > norepinephrine > phenylephrine. Responses to clonidine were trivial (< 5% of maximum) and remained < 25% of maximum in the presence of subthreshold concentrations of angiotensin II. A weak trend for increased potency of alpha-methylnorepinephrine was noted in arteries of subjects with higher blood pressures (r = 0.268, p = 0.027). There was no relationship between blood pressure and pA2 for yohimbine. The pA2 for prazosin could not be calculated because of a decline in maximal responses but prazosin was clearly more potent than yohimbine. The decline in maximal responses to norepinephrine and phenylephrine after prazosin treatment was related to subjects' diastolic blood pressures (r = -0.400, p = 0.003). There were no significant relationships between these measurements of vascular responsiveness and a family history of hypertension. There were also no significant relationships between these measurements of vascular responsiveness and plasma norepinephrine levels, alpha 2-adrenoceptor binding or platelets of beta 2-adrenoceptor binding of lymphocytes. The major postjunctional alpha-adrenoceptors in this artery are of the alpha 1 type. The data suggest that differences in potency of alpha-adrenoceptor agonists in relation to blood pressure may be due to differences in the alpha 2-adrenoceptor but are not likely due to a difference in binding to the receptor itself.(ABSTRACT TRUNCATED AT 250 WORDS)