Endothelial modulation of vascular relaxation to nitrovasodilators in aging and hypertension

Blood vessel responses to relaxant drugs have been reported to change with aging and with the development of hypertension. In view of the requirement of endothelial cells for the activity of many relaxant drugs, we examined the role of the endothelium in the relaxation response of vascular tissue. Aortic and mesenteric ring segments from normotensive and hypertensive rats, ages 5 to 6, 15 to 18 and 30 to 31 weeks, were examined for relaxation to sodium nitroprusside, sodium nitrite, atrial natriuretic factor and 8-bromo-cyclic GMP. Relaxation responses to the nitrovasodilators were reduced progressively with aging in ring segments of Wistar-Kyoto rats (WKYs) and spontaneously hypertensive rats (SHRs) with intact endothelium; however, intact SHR ring preparations displayed less relaxation to nitrovasodilators at 15 to 18 and 30 to 31 weeks than those of WKYs. Rubbed (endothelium denuded) ring preparations displayed greatest relaxation to nitrovasodilators with no difference being observed between SHR and WKY preparations at any age tested. Relaxation to atrial natriuretic factor and 8-bromo-cyclic GMP was not different between rubbed and unrubbed ring segments or between SHRs and WKYs, indicating no detectable impairment of the overall relaxation response in the vascular smooth muscle of SHRs. These results suggest that the total functional capacity of vascular smooth muscle to relax to nitrovasodilators is not changed with aging or hypertension. However, the endothelial cells exert modulatory influences upon the vascular smooth muscle to reduce overall responsiveness to nitrovasodilators, an effect that is enhanced with aging and the development of genetic hypertension.