Endothelium-dependent inhibition of the use of extracellular calcium for the arterial response to vasoconstrictor agents.

The responses of rabbit mesenteric or coeliac artery rings to angiotensin II or adrenaline (but not to K+) were enhanced by endothelium destruction (by rubbing). Potentiation by indomethacin of the response to the agonists was observed in rubbed rings but not in intact ones. Both angiotensin II and adrenaline (in the presence of propranolol and prazosin) induced endothelium-dependent relaxation of the arteries. Rubbed rings, but not intact ones, contracted when Ca2+ was added to a previously Ca2+-free medium containing angiotensin II or adrenaline. The vasoconstrictor response appears to be modulated by the regulation of receptor-operated Ca2+ channels through EDRF released by the endothelium and by some cyclo-oxygenase product at the level of the smooth muscle cell membrane.