Effect of endothelium on the aortic contraction induced by norepinephrine and KCl in isolated rat aorta.

Endothelium in aorta is known to contain releasable vasoactive agents. The purpose of the present study was to examine the effect of endothelium on the contraction induced by the membrane depolarizing agent KCl and by the alpha adrenoceptor agonist norepinephrine. It was found that the contraction induced by norepinephrine was bigger in denuded aorta at 1 x 10(-9) M and 1 x 10(-8) M norepinephrine, but the norepinephrine-induced contraction at 1 x 10(-7) M norepinephrine was not different between the denuded and control aortae. On the other hand, the contraction induced by KCl in denuded aorta was bigger at 10 mM KCl but smaller at 60 and 90 mM KCl in comparing with those determined in the presence of endothelium. These results indicate that the presence of endothelium alleviates the norepinephrine-induced contraction below 1 x 10(-7) M norepinephrine but potentiates the KCl-induced contraction at 60 mM KCl and above.