In vitro investigation of the effect of prostaglandins and nonsteroidal anti-inflammatory drugs on contractile activity of the equine smooth muscle of the dorsal colon, ventral colon, and pelvic flexure

Objectives-To determine the in vitro effect of prostaglandin E-2 (PGE(2)), PGF(2 alpha), PGI(2); and nonsteroidal anti-inflammatory drugs (NSAID; ie, flunixin meglumine, ketoprofen, carprofen, and phenylbutazone) on contracti le activity of the equine dorsal colon, ventral colon, and pelvic flexure c ircular and longitudinal smooth muscle. Animals-26 healthy horses. Procedure-Tissue collected from the ventral colon, dorsal colon, and pelvic flexure was cut into strips and mounted in a tissue bath system where cont ractile strength was determined. incremental doses of PGE(2), PGF(2 alpha), PGI(2), flunixin meglumine, carprofen, ketoprofen, and phenylbutazone were added to the baths, and the contractile activity was recorded for each loc ation and orientation of smooth muscle. Results-In substance P-stimulated tissues, PGE(2) and PGF(2 alpha) enhanced contractility in the longitudinal smooth muscle with a decrease or no effe ct on circular smooth muscle activity. Prostaglandin I-2 inhibited the circ ular smooth muscle response with no effect on the longitudinal muscle. The activity of NSAID was predominantly inhibitory regardless of location or mu scle orientation. Conclusions and Clinical Relevance-In the equine large intestine, exogenous prostaglandins had a variable effect on contractile activity, depending on the location in the colon and orientation of the smooth muscle. The admini stration of NSAID inhibited contractility, with flunixin meglumine generall y inducing the most profound inhibition relative to the other NSAID evaluat ed in substance P-stimulated smooth muscle of the large intestine. The resu lts of this study indicate that prolonged use of NSAID may potentially pred ispose horses to develop gastrointestinal tract stasis and subsequent impac tion.