IN VIVO DIRECT EFFECTS OF CHOLINERGIC AGENTS ON THE INFERIOR MESENTERIC AND CARDIAC GANGLIA WITH RELATION TO THEIR RECEPTORS IN THE DOG

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The relative contribution of nicotinic and muscarinic receptors to the cholinergic transmission of the inferior mesenteric ganglion was studied in spinal dogs by recording changes in perfusion pressure of the inferior mesenteric artery as an indicator of ganglionic function. Preganglionic stimulation elicited a frequency (2.5-320 Hz)-dependent rise in the perfusion pressure, which was inhibited by i.v. hexamethonium (C6) (10 mg/kg) or atropine (0.1 mg/kg) administered after C6. Acetylcholine (ACh) (0.1-1000 μg) administered into the inferior mesenteric artery to reach the mesenteric ganglion induced a dose-dependent rise in perfusion pressure and this dose-response curve was shifted to the right by C6 or atropine. Bethanechol (1-1000 μg) i.a. produced a dose-dependent rise in the pressure, which was abolished after i.v. atropine. Tetramethylammonium (1-300 μg) i.a. elicited an increase in the pressure though the effects were decreased at larger doses, and these effects were strongly inhibited by i.v. C6. ACh (5-1000 μg) administered into the right subclavian artery to reach the cardiac sympathetic ganglia caused a dose-dependent positive chronotropic effect, which was inhibited by i.a. C6 or atropine. The results suggest that the inferior mesenteric ganglion seems to differ from the cardiac ganglia in relative contribution of nicotinic and muscarinic receptors to the cholinergic transmission.
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