In vitro investigation of the interaction between nitric oxide and cyclo-oxygenase activity in equine ventral colon smooth muscle

The objective of this study was to determine if a correlation exists between the presence of nitric oxide and prostaglandin release in the equine ventral colon smooth muscle, since this relationship may accentuate the inflammatory process during intestinal injury. Tissue was collected from the ventral colon, cut into muscle strips oriented along the circular, longitudinal and taenial layers, and mounted in a tissue bath system. Samples of the bath fluid were collected before, following electrical field stimulation (EFS), and following EFS in the presence of L-NAME, a nitric oxide synthase inhibitor. Muscle strips were also obtained following systemic administration of a cyclo-oxygnease inhibitor and samples were collected using the previously described protocol. Concentrations of prostaglandins were determined in the fluid samples using an ELISA. Electrical field stimulated release of nitric oxide produced a significant increase in prostaglandin production which did not occur in the presence of L-NAME. Systemic administration of flunixin meglumine reduced prostaglandin levels at all sampling periods, although a small increase was present following EFS. The results of this study support the hypothesis that there is a correlation between the release of nitric oxide and the production of prostaglandins in the smooth muscle of the large colon. This association between nitric oxide and prostaglandin may act as an important regulatory mechanism for various physiological mechanisms, such as vascular smooth muscle tone, and may contribute to amplified tissue injury when the induced forms of both enzymes are activated during an inflammatory insult. This suggests that the use and development of COX2 and iNOS inhibitors may help attenuate the inflammatory response following intestinal injury.