Altered vascular beta adrenoceptor-mediated relaxation in deoxycorticosterone-salt hypertensive rats

Beta adrenoceptor-mediated relaxation was studied on femoral and mesenteric arteries and thoracic aorta from deoxycorticosterone-salt hypertensive and age-matched normotensive rats. Maximum relaxations to isoproterenol (ISO), fenoterol and norepinephrine were less in hypertensive than in normotensive tissues. Mean negative log EC50 values of ISO and norepinephrine, but not fenoterol, were smaller in femoral and mesenteric strips from hypertensive rats than those from oil-water-treated rats. In thoracic aortas from hypertensive rats, the mean negative log EC50 values of ISO and fenoterol decreased, whereas those of norepinephrine increased as compared with those in oil-water-treated rats. In oil-salt- and deoxycorticosterone-water-treated rats, hypertension did not develop nor were the responses to ISO reduced. Relative potencies of the beta adrenoceptor agonists and Schild plot data for atenolol and butoxamine indicate that femoral arteries of normotensive and hypertensive rats possess beta-1 adrenoceptors mediating relaxation. It also is suggested that the mesenteric artery and thoracic aorta of both normotensive and hypertensive rats predominantly possess beta-2 adrenoceptors mediating relaxation. The present results suggest that an elevation in blood pressure is associated with the reduction of beta-1 adrenoceptor-mediated relaxation in femoral arteries and of beta-2 adrenoceptor-mediated relaxation in mesenteric arteries.