Direct pharmacological comparison of the muscarinic receptors mediating relaxation and contraction in the rabbit thoracic aorta

The purpose of the present studies was to directly compare the pharmacology of the muscarinic cholinergic receptors coupled to carbachol-induced relaxation and contraction of the intact and the endothelium-denuded rabbit thoracic aorta, respectively. The order of potencies of agonists for producing relaxation in the intact aorta was similar to that for producing contraction in the denuded aorta. In both preparations, the partial agonists pilocarpine, McN-A-343, and RS86 functioned as antagonists, indicating a lack of receptor reserve in both preparations. Further, the pA(2) values for antagonists in both tissues were virtually identical and were consistent with the pharmacology of M-3 receptors. (C) 1999 Elsevier Science Inc. All rights reserved.