EFFECT OF AGING AND HYPERTENSION ON ENDOTHELIAL MODULATION OF OUABAIN-INDUCED CONTRACTION AND SODIUM-PUMP ACTIVITY IN THE RAT AORTA

Objective To investigate the endothelial modulation of the rat thoraci c aorta sodium-potassium ATPase activity and its possible alteration b y ageing and hypertension. Methods Male spontaneously hypertensive rat s (SHR) and Wistar-Kyoto rats (WKY) aged 5 weeks, 3, 6, 12 and 18 mont hs were anaesthetized. Their aortae were dissected and divided into cy lindrical segments and vasomotor responses obtained in segments with o r without endothelium were recorded on a polygraph. Results Endotheliu m removal increased ouabain responses in young (aged 3 and 6 months) W KY rat aortic segments, but reduced those obtained in old (aged 18 mon ths) WKY rat segments and in segments from SHR aged 3, 6 and 12 months . An enhancement of contractions in response to ouabain with age was o bserved in both strains, but it occurred at earlier ages in vessels fr om SHR. At ages 3 and 6 months, responses to ouabain were higher in in tact vessels from SHR than they were in those from WKY, but were lower in endothelium-denuded vessels, In aortic segments from 6-month-old W KY rats and SHR, ouabain reduced or abolished potassium-induced relaxa tions in segments with or without endothelium, respectively. In vessel s from SHR and WKY rats aged 18 months, ouabain abolished potassium-in duced relaxations both in intact and in endothelium-denuded vessels. C onclusions Endothelium of WKY rat aorta might release a factor in resp onse to ouabain that modulates its contraction negatively. Endothelium of SHR and old WKY rat aorta releases a contracting factor that modul ates ouabain contractions positively, Thus, the inhibitory effect of e ndothelium on contractions induced by ouabain might be lost as a conse quence both of hypertension and of age, being replaced by an endotheli um-dependent contracting factor that facilitates ouabain responses.