Decreased modulation by endothelium of noradrenaline-induced contractions in aorta from stroke-prone spontaneously hypertensive rats.

Influences of endothelium on contractions of aortic ring preparations from 15 to 17 weeks old stroke-prone spontaneously hypertensive rats (SHRSP) and age-matched Wistar-Kyoto rats (WKY) were compared. Noradrenaline-induced contraction was potentiated by endothelium removal; the potentiation was greater in the WKY aorta. Noradrenaline (10(-5) M) induced a biphasic contraction in endothelium-intact WKY aorta, while endothelium-intact SHRSP aorta or endothelium-removed preparations of both strains showed a monophasic sustained contraction. The tension changes in high-K-induced contracture of the endothelium-intact preparation was less pronounced in both WKY and SHRSP aortae. The relaxation by acetylcholine (10(-5) M) of endothelium-intact aortae, precontracted with noradrenaline (5 X 10(-7) M), amounted to 78% in the WKY and to 44% in the SHRSP preparation. In endothelium-removed aortae, sodium nitroprusside induced a comparable relaxation in both WKY and SHRSP preparations. These results indicate that the endothelium plays an important role in controlling the noradrenaline-induced contraction and that the lower influence of endothelium in the SHRSP aorta is most likely due to a decreased activity of this endothelium.