Contractile and endothelium-dependent dilatation aortic reactions in hyperthyroidism

То prove the hypothesis that onset of hyperthyroidism may be attributed not only to hyperactivity of beta-adrenergic system but also to enhanced endothelial impacts on the tone of smooth muscle cells, the authors studied the role of endothelium in regulation of functional activity of arterial vessels in hypothyroidism. The experiments were made on isolated aortic segments of euthyroid and hyperthyroid female rats. Contractile and endothelium-dependent dilatations of the aortic segments in response to noradrenaline and carbacholine, respectively, were studied. It was shown that in hyperthyroidism contractile reactions of the aorta to noradrenalin are less expressed as a result of low sensitivity of the smooth muscle cells to this agonist and strong inhibitory effect of endothelium on these reactions. Dilatatory endothelium-dependent reactions of the isolated aorta in hyperthyroidism are more expressed. Enhancement of carbacholine dilatotory effects may be due to endothelial hyperpolarising factor, whose eficiency grows with a thyroxin-stimulated rise in the number of units of the Na*K*A TPase pump. The findings indicate an essential role of endothelium in mechanisms of hyperthyroid circulatory disorders.