THE ROLE OF ANTIOXIDANT ENZYMES IN THE CONTROL OF OPOSSUM SPHINCTER OF ODDI MOTILITY

Superoxide rapidly oxidizes nitric oxide (NO) to form peroxynitrite, t hus terminating the biological activity of NO. The aims of our study w ere to determine if superoxide alters the motor function of the sphinc ter of Oddi and to localize the antioxidant enzymes in the sphincter o f Oddi. Immunostaining was performed and enzyme activities were measur ed in the sphincter of Oddi. In physiological experiments, force-displ acement transducers recorded tension in the spontaneously contracting sphincter of Oddi and after electrical field stimulation (EFS) of prec ontracted sphincter of Oddi. Superoxide was generated by the addition of xantkine with xanthine oxidase, superoxide radicals were scavenged by the addition of superoxide dismutase (SOD), and catalase or SOD was inhibited by diethyldithiocarbamic acid. Immunostaining demonstrated SOD and catalase immunoreactivity in ganglia situated at the serosal s urface of the circular muscle. Total SOD activity was 202 +/- 12 U/mg. Generation of superoxide or inhibition of SOD increased the contracti le frequency and decreased relaxation after EFS. We conclude that supe roxide alters sphincter of Oddi motor function, and the presence of su peroxide scavenging enzymes in enteric plexuses suggests that they may regulate sphincter of Oddi neuromuscular function by clearing endogen ous superoxide.