EFFECTS OF AGING AND HYPERTENSION ON THE REACTIVITY OF ISOLATED CONDUIT AND RESISTANCE VESSELS

We have studied the effects of hypertension and aging on the concentra tion-response curves for alpha(1)-adrenoceptor-mediated vasoconstricti on and methacholine-induced endothelium-dependent relaxation. The expe riments were performed in aortic rings and in perfused mesenteric vasc ular bed preparations taken from WKY rats, from SHR of 16-18, 28-30, a nd 58-60 weeks, and from 16- to 18-week-old SHRSP rats, respectively. The influence of aging and/or hypertension caused no alterations of th e alpha(1)-agonist response provoked by phenylephrine in aortic rings. Mesenteric vascular bed preparations showed an increase in maximal re sponse to methoxamine when taken from hypertensive animals. Age per se did not change the contraction in the mesenteric arteries. Hypertensi on in combination with age caused a decrease in endothelium-dependent vasodilation induced by methacholine in aortic rings, but not in mesen teric arteries. However, the sensitivity to methacholine decreased age -dependently in the mesenteric vascular bed preparation taken from the WKY and SHR. The endothelium-independent relaxation induced by sodium nitroprusside showed a decrease in sensitivity in aortic rings taken from 58- to 60-week-old SHR when compared with the age-matched WKY. Th ese findings suggest that the mechanisms beyond the endothelium involv ed in vasodilation are not responsible for the decreased methacholine- induced relaxation in aortic rings. It is concluded that (1) the respo nsiveness of resistance arteries to adrenoceptor stimulation only chan ges with elevated blood pressure and (2) hypertension in combination w ith aging induces an endothelial dysfunction in conduit arteries but n ot in resistance vessels. (C) 1994 Academic Press, Inc.