Loperamide reduces the intestinal secretion but not the mucosal cAMP accumulation induced by choleratoxin.

The effect of loperamide on net fluid transport and epithelial cAMP accumulation was tested in choleratoxin-exposed ligated colon loops of the rat in vivo. Purified choleratoxin (50 micrograms/ml saline, for 5 h) induced net secretion and doubled cAMP levels in comparison with saline-treated controls. Loperamide (4 mg/kg intragastrically) reduced this secretion by 75%, without diminishing cAMP accumulation; it had no effect on basal fluid transport or cAMP. The data suggest that the opiate analogue interferes with the secretory process at a point beyond the cAMP increase caused by activation of adenylate cyclase.