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The muscarinic receptor mediating vasodilation of resistance vesse]s in the rat iso]ated, constant-pressure perfused kidney vasodilation disappeared after destruction of the endothelium with detergent. Highly significant correlations of agonist potencies for vasodilation were found between rat kidney and guinea-pig ileum submucosal arterioles as weH as agonist potencies at smooth muscle muscarinic M 3 receptors of the guinea-pig ileum. The rank order of antagonist potencies (4-diphenylacetoxy-Nmethylpiperidine methiodide (4-DAMP) > (R)-hexahydro-difenidol -hexahydro-sila-difenidol > pirenzepine -p-fluorohexahydro-sila-difenidol-himbacine-AF-DX 384-AQ-RA 741 > (S)-hexahydro-difenidol) to attenuate vasodilation to APE in rat kidney, correlated significantly with affinities at M 3 receptors in submucosal arterioles and in smooth muscle of the guinea-pig ileum, but differed from those at M 1 and M 2 receptors in rabbit vas deferens. The agonist and antagonist potencies suggest that vasodilation elicited by muscarinic stimuli in endothelium-intact rat renal vasculature is mediated by functional muscarinic M 3 rcceptors.

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