A Study of Drug Receptors in the Isolated Rabbit Aorta Strip

摘要

An investigation was made to determine whether the action of acetylcholine is caused by the release of catecholamine from stores in the aortic wall or whether there is a cholinoreceptive site in this tissue. Isotonic contractions were recorded using isolated helical strips of rabbit aorta suspended in a bath of 95 percent 0 sub 2and 5 percent CO sub 2- saturated, phosphate-buffered Kreb's solution maintained at a constant temperature of 37 degrees C. Acetylcholine, epinephrine, and antagonists to each (atropine, dichloroisoporterenol) were added directly to the tissue-bathing fluid with a syringe. Epinephrine and acetylcholine, at dose levels used, have only excitatory effects on the isolated rabbit aorta. At no concentration of acetylcholine was a relaxing effect observed. The sensitivity of the muscle to epinephrine and to acetylcholine is in the ratio of 1:100; the threshold concentration for epinephrine is 1 X 10 to the power of minus 8 M. The rabbit aorta has a distinct myogenic cholinoreceptive site, and the excitatory effect is not caused by a catecholamine releasing mechanism, which possibly exists in other parts of the vascular tree. (Author)