Regulation of vascular tone by endothelium, nerve and blood cells through their reciprocal actions.

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We investigated the effects of endothelium, adventitia (nerve), and blood cells(white blood cells : WBC) on vascular tone during hypoxia or acidosis. Hypoxia contracted blood vessels. Removal of endothelium attenuated the hypoxia-induced contraction of blood vessels. Cyclooxygenase inhibitors attenuated the hypoxia-induced contraction of blood vessels, suggesting that cyclooxygenase related eicosanoids may be released from endothlium during hypoxia. In contrast, removal of endothlium and adventitia abolished the hypoxia-induced contraction. These findings syggest that adventitia as well as endothlium may contribute to the hypoxia-induced contraction. It was also found that acidosis attnuated the agonist-induced contraction in a different manner depending the type of agonists used, and that endothelium facilitated the attenuated action of acidosis on agonist-induced contraction. From the experiment concerning the effect of WBC on vascular tone, we found that WBC dilates vascular smooth muscle indirectly through endothlium. We investigated the substance released from endothelium using some kinds of antagonists. However, we could not detect the substance. It has been reported that shear stress on endothelium releases endothlium-derived relaxing substance(s). Applying these phenomenon to research in testing human endothelial function, we found that endothelium did not work well in some kind of disease. In summary we found that endothelium, adventitia and blood vessels regulate vascular tone through their reciprocal actions.