The action of loperamide in inhibiting prostaglandin-induced intestinal secretion in the rat.

1 The mechanisms by which loperamide inhibits the intestinal secretion induced by prostaglandin E2 were investigated in rat jejunum. 2 In vivo loperamide prevented prostaglandin-induced fluid secretion but did not reduce the associated rise in the transintestinal potential difference. 3 In intestinal sheets the electrical response to prostaglandin E2 was enhanced in the presence of loperamide. 4 The ionic basis of these changes was determined by measuring Na+ and Cl- fluxes across intestinal sheets. Loperamide did not reduce the prostaglandin-induced increase in net Cl- secretion, although it prevented the inhibition of mucosal-to-serosal Na+ movement. 5 Loperamide does not alter cyclic adenosine 3',5'-monophosphate (cyclic AMP) levels by a direct action at the enterocyte, since in isolated enterocytes neither basal nor prostaglandin-stimulated cyclic AMP levels were affected by the drug.