Changes in endothelium-dependent vascular responses associated with spontaneous hypertension and age in rats.

The aim of this study was to investigate if the endothelium-dependent relaxation and the inhibitory effect of endothelium against vasoconstrictor stimuli are reduced by aging and hypertension in rat aorta. Both relaxation and isometric contraction of intact and denuded aortic rings from spontaneously hypertensive rats (SHR) of 7-9, 12-18, 28-36 and more than 70 weeks old and from age-matched Wistar-Kyoto rats (WKY) were measured in parallel. An age-related decrease of endothelium-dependent relaxation to acetylcholine was found, which was greater in arteries from SHR (p < 0.05). Indomethacin normalized the endothelium-dependent relaxations in aortic rings from either old or hypertensive rats. Relaxations elicited by nitroglycerin were slightly enhanced with age in both WKY and SHR (p < 0.05). Moreover, endothelium removal increased responsiveness to indanidine and to 5-hydroxytryptamine (5-HT). Endothelium-dependent inhibition on the contraction decreased with aging (to a greater extent in SHR). These results indicate that aging and hypertension are associated with a decrease in the endothelium-dependent responses. Endothelium-dependent relaxations of aortae from old normotensive and hypertensive rats were impaired by the production of a cyclooxygenase-derived contractile factor. However, the higher response to nitroglycerin suggests a lesser production of endogenous nitric oxide by endothelial cells.