The effects of deoxycholic and ricinoleic acid on the isolated circular muscle of the cat colon are modified by leucine-enkephalin.

The mechanism of the diarrheogenic effect of bile acids and fatty acids is incompletely understood. In order to study their effects on motility we tested sodium deoxycholate and sodium ricinoleate in their actions on the spontaneous mechanical and myoelectrical activity of the isolated circular muscle of the cat colon in a perfusion apparatus. Sodium deoxycholate activated the muscle in concentrations from 10(-9) to 10(-5) M. ED50 was 6.3 X 10(-9) M, ED100 10(-6) M. Sodium ricinoleate similarly stimulated muscle contractions. ED50 was 2.3 X 10(-7) M, ED100 5.1 X 10(-6) M. Both agents increased the occurrence of oscillating potentials in the myoelectrical records. Oscillations probably correspond to the migrating electrical complexes in diarrhea. The addition of leucine-enkephalin augmented primarily the number of brief spike potentials which may correspond to segmenting contractions. Thus, bile acids and fatty acids cause profound changes in colonic motility which by themselves may promote diarrhea. The endogenous opiate leucine-enkephalin could possibly counteract these effects.