Pharmacological studies of loperamide, an anti-diarrheal agent. II. Effects on peristalsis of the small intestine and colon in guinea pigs

Effects of loperamide on peristalsis in the guinea pig intestines were investigated in comparison with those of morphine and atropine. The following results were obtained. The ejection of intraluminal fluid produced by the peristaltic contraction of the isolated ileum was suppressed by loperamide at a concentration of 10-8 or 2 × 10--8 g/ml. Peristalsis in the intestinal loop of anesthetized guinea pigs was inhibited by i.v. administration of loperamide at a dose of 0.03 mg/kg. Morphine (0.03 mg/kg i.v.) and atropine (0.05 mg/kg i.v.) also inhibited the peristaltic contraction. The effect of loperamide continued longer than that of morphine. Peristalsis in the colonic loop of anesthetized guinea pigs was inhibited by i.v. administration of loperamide at a dose of 0.01 or 0.03 mg/kg. Morphine (0.1 mg/kg i.v.) and atropine (0.03 mg/kg ix.) also inhibited the peristaltic contraction of the colonic loop. Loperamide (0.01 or 0.03 mg/kg i.v.) and morphine (0.1 mg/ kg i.v.) caused a slight and temporary increase of resting level of intraluminal pressure with inhibition of peristalsis in the colonic loop. These results suggest that loperamide suppresses the peristaltic contraction caused by distension of the intestinal lumen.