THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Copyright © 1989 by The American Society for Pharmacology and Experimental Therapeutics Evidence for Muscarinic Inhibitory Neurotransmission in Rodent

The influence of cholinergic and noncholinergic inhibitory nerves was examined in circular and longitudinal muscle from the duo-denum. Rodent proximal small intestine was cut into strips measuring 6.0 x 10.0 mm. Strips cut along the oral-caudal axis were called longitudinal strips, whereas those cut 90#{176}to that axis were called circular strips. The strips were stretched to their optimal lengths and subjected to electrical field stimulation in the presence of various concentrations of atropine, pirenzepine or McN-A-343-1 1. All three drugs inhibited field-stimulated contrac-tion responses and produced or augmented relaxation responses in both muscle layers. All relaxation responses were abolished by tetrodotoxin, indicating they were due to excitation of inhibi-tory nerves. For each response examined atropine was signifi-cantly more potent than pirenzepine (relative potency ratio