α 2‐Adrenoceptors and endothelium‐dependent relaxation in canine large arteries

Abstract

Ring preparations from the carotid, coronary, renal, mesenteric and femoral arteries of the dog were precontracted with the thromboxane mimetic U46619, after ensuring that the resting conditions were comparable from the Laplace relationship. In the presence of prazosin (1 μm) and propranolol (3 μm), noradrenaline (NA) relaxed the arteries in the order coronary > carotid > femoral > renal = mesenteric. When maximum relaxation to nitroglycerin (10 μm) was taken to be 100% the maximum relaxation to noradrenaline in each artery was: coronary 70%; carotid 34%; femoral 19%; renal 7% and mesenteric 2%. In endothelium‐intact arteries UK 14304 mimicked the relaxation responses to NA and idazoxan shif..