PHARMACOLOGICAL CHARACTERIZATION OF MUSCARINIC RECEPTORS IN THE RAT MESENTERIC VASCULAR BED

The nature of the muscarinic receptor subtype mediating acetylcholine-induced relaxation in the mesenteric vascular bed of the rat was investigated under conditions of flow in a perfused preparation. The ability of atropine, pirenzepine, AF-DX 116 and 4-DAMP to block the relaxation response was estimated. The low affinity of AF-DX 116 (pA2 = 6.08) for these receptors, together with the intermediate affinity of pirenzepine (pA2 = 6.90) tend to exclude the M1 and M2 pharmacological subtype of receptors as the primary mediators of the cholinergic relaxation. In contrast, atropine and 4-DAMP potently inhibited the response, with pA2 values of 9.61 and 10.1, respectively. The overall results suggest that a receptor similar to the pharmacological M3 receptor subtype is responsible for the cholinergic relaxation of the mesenteric vascular bed of the rat.