Interactions of endothelial cells and smooth muscle cells of arteries.

Relaxation of selected isolated arteries by acetylcholine, bradykinin, and certain other vasodilators is mediated by a factor released from endothelial cells. Relaxation by the factor (chemical identity still unknown) is accompanied by an increase of cyclic GMP. The finding that hemoglobin inhibits both endothelium-dependent relaxation and the increase in cyclic GMP may have pathophysiologic relevance.