Inhibition by loperamide of mucus secretion in the rat colon in vivo.

The effect of loperamide on mucus secretion and the net transport of fluid, sodium and potassium was investigated in the perfused rat colon in vivo. Prostaglandin E2 (PGE2, 1 mg/kg per h intraarterially) and deoxycholic acid (2 mM intraluminally) were used as secretagogues. Mucus secretion was determined as the total amount of protein-bound hexose in the effluent. Under basal conditions, loperamide (6 mg/kg subcutaneously) slightly decreased mucus secretion and increased the absorption of fluid and sodium. PGE2 and deoxycholic acid stimulated mucus secretion about 4- and 9-fold, respectively. Loperamide abolished the mucus secretory response to PGE2 and reduced the response to deoxycholic acid by 50%. It also reduced the fluid secretion following PGE2 but did not affect the diminished fluid absorption following deoxycholic acid. Potassium secretion was not significantly influenced by loperamide and therefore was independent of the secretion of mucus. The data suggest that loperamide is a potent inhibitor of colonic mucus secretion, a property that possibly contributes to the antidiarrheal effect of this opiate analogue.