Studies in vivo and in vitro on effects of PGE2 on colonic motility in rabbits.

Prostaglandins (PG) of the E series are synthesized throughout the gastrointestinal tract, and their elevated levels have been reported in many diarrheal states, including inflammatory bowel disease. It is already known that PGE2 has region-specific and muscle layer-specific effects in different areas of the intestine. The aim of this study was to evaluate possible dose-related motor effects of PGE2 on rabbit proximal and distal colon both in vivo and in vitro. We found that, in the proximal colon in vivo, PGE2 caused inhibition of myoelectric and mechanical activity at low doses but at higher doses caused marked excitation. Under the same experimental conditions, PGE2 caused only excitation in the distal colon, a phenomenon associated with an increase in antegrade contractions and diarrhea. In vitro, PGE2 caused excitation of both proximal and distal colonic longitudinal muscle and relaxation of the circular muscle. Its actions, however, were much more pronounced in the distal region. It is concluded that PGE2 has profound effects on colonic motility that are concentration dependent and that differ with the region of the colon under study. Furthermore, the evidence also suggests that elevated PGE2 levels in disease states may play a significant role in abnormal colonic motility and may facilitate the onset of diarrhea.