Ricinoleic acid and loperamide have opposite motor effects in the small and large intestine of the cat.

The actions of laxatives and antidiarrheal agents in the gut are incompletely understood. Therefore, the effects of Na ricinoleate 10(-4)-10(-2) g/kg b. w. and of loperamide 10(-4) g/kg b. w. on myoelectric activity and marker propulsion were studied in the small and large intestine of 7 unanesthetized cats. Intraduodenal application of ricinoleate briefly increased and then decreased spike activity in the small intestine; marker transit was delayed (92 +/- 18 min vs. 55 +/- 14 min in controls). Ricinoleate also initiated spike complexes of 10-215 sec duration. Transit from the right to the left colon was sometimes accelerated and sometimes delayed. The number of uncoupled slow waves was increased to 278% of control. Loperamide accelerated small intestinal transit to 17 +/- 6 min and markedly delayed it in the colon. At the same time it caused a strong and prolonged rise in colonic spike activity. When ricinoleate and loperamide were given together, their effects almost compensated for each other. The resulting net effect was similar to the data in the control experiments. It is concluded that laxatives and antidiarrheal agents alter not only transit, but also myoelectric activity in the small and large intestine. The effects are largely in opposite direction. Loperamide may, therefore, antagonize motor effects of ricinoleate in the gut.