Nitric oxide‐dependent relaxation induced by M1 muscarinic receptor activation in the rat small intestine

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Abstract
The aim of the present study was to investigate whether muscarinic M1 receptor activation induces intestinal relaxation via nerve-dependent nitric oxide formation. Mechanical activity in longitudinal segments of rat jejunum was recorded isotonically in organ baths. The muscarinic M1 receptor agonist 4-[[[(3-Chlorophenyl)amino]carbonyl]oxy]-N,N,N,-trimethyl-2-butyn- 1-ammonium chloride (McN-A-343, 10(-7)-10(-4) M) induced a concentration-dependent relaxation of rat jejunum. Relaxations induced by McN-A-343 (10(-5) M) were inhibited by the M1 receptor antagonist telenzepine (10(-8) M), and enhanced by the M3 receptor antagonist para-fluorohexahydrosiladifenidol (p-F-HHSiD; 3x10(-7) M). The inhibitory responses induced by McN-A-343 were abolished by the nitric oxide synthase inhibitors Nomega-nitro-L-arginine (L-NOARG; 10(-4) M) and Nomega-monomethyl-L-arginine (L-NMMA; 3x10(-5) M), the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ; 10(-5) M), and by tetrodotoxin (TTX; 3x10(-7) M). Guanethidine or hexamethonium did not affect inhibitory responses induced by McN-A-343. In conclusion, McN-A-343 induces nerve-dependent, nitrergic relaxations in rat jejunum, via activation of muscarinic M1 receptors. Hence, selective muscarinic M1 receptor agonists or antagonists might offer possibilities for pharmacological manipulation of the NO system.