Mediation of contraction by cholinergic muscarinic receptors in the ureterovesical junction

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Abstract
1. The muscarinic receptor profile of the sheep ureterovesical junction has been studied by means of in vitro techniques. The relative potency (pD2 = -log EC50) and maximum effect (Emax) observed with carbachol were 51-fold and 25% greater than with acetylcholine respectively. This could be due to the presence of active acetylcholinesterase in this tissue. 2. The pA2 values obtained with the muscarinic antagonists were pirenzepine (8.52), AF-DX 116 (8.05), 4-DAMP (9.41) and hexahydroxiladifenidol (8.66). The slope values of Schild plots were not significantly different from unity, indicating competitive antagonism. Furthermore, when the slopes were constrained to 1, no significant differences were found between the pA2 values. These pA2 values were similar to those observed in other mammalian smooth muscles. 3. It is concluded that muscarinic receptors in the sheep ureterovesical junction smooth muscle belong to the M1, M2 and M3 subtypes and mediate contraction of the ureterovesical junction, which suggests that during parasympathetic stimulation they might prevent vesicoureteral reflux.