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

Abstract
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 (50μg/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.