INHIBITORY EFFECTS OF VARIOUS SPASMOLYTICS ON THE VAGAL AFFERENT GASTRIC EXCITATORY RESPONSE IN CATS

The inhibitory effects of atropine, cimetropium, pirenzepine and N-but ylscopolamine on the vagal afferent gastric excitatory response in cat s under anesthesia with pentobarbital sodium and infusion of gallamine were examined. Electrical stimulation of vagal trunk in left side (10 Hz in frequency, 3 msec in duration, 15 V in intensity and for 10 sec ) caused an initial gastric excitatory response during the period of s timulation followed by a late excitatory gastric response after stimul ation in normal cats. The initial response was inhibited by atropine ( 100 mu g/kg, i.v.) and hexamethonium (10 mg/kg, i.v.), while the late response was inhibited by atropine but not by hexamethonium (10 mg/kg, i.v.). In chronic supranodose vagotomized cats 11 - 15 days after the operation, stimulation of the vagal trunk caused a late gastric excit atory response after the stimulation period, which was inhibited by at ropine (100 mu g/kg, i.v.) but not by hexamethonium (10 mg/kg, i.v.). The two types of gastric responses in normal cats have been defined as follows: the initial gastric excitatory response (atropine- and hexam ethonium- sensitive) is due to activation of vagal efferent fibers and the late gastric excitatory response (atropine-sensitive and hexameth onium-resistant) is due to activation of vagal efferent fibers. ED50 v alues of atropine, cimetropium, pirenzepine and N-butylscopolamine in inhibiting the vagal afferent gastric response were 7.2 mu g/kg (n=4), 2.4 mu g/kg (n=6), 82.6 mu g/kg (n=3) and 93.0 mu g/kg (n=4), respect ively. The inhibitory effects of atropine and cimetropium on the vagal efferent gastric excitatory response (hexamethonium-resistant) were m ore potent than those of pirenzepine end N-butylscopolamine. These res ults suggested that the potent inhibitory effects of cimetropium and a tropine on the vagal afferent gastric response may involve a potent sp asmolytic effect.