Endogenous prostaglandin E and contractile activity of isolated ileal smooth muscle.

The effects of endogenous prostaglandin E (PGE) on the contractile activity of isolated cat ileal muscle rings were studied. Force development in circularly oriented muscle fibers were recorded. The muscles contained a mean basal PGE concentration of 1 +/- 0.6 ng PGE per g wet wt (mean +/- SE) as measured by radioimmunoassay. Acetylcholine (ACh) or elevated potassium caused contractions and enhanced PGE concentration (P less than 0.05). Removing Ca2+ from high potassium solutions blocked contraction, but PGE concentration still increased (P less than 0.02). The prostaglandin synthetase inhibitors, indomethacin and 5,8,11,14-eicosatetraenoic acid (ETA) reduced PGE concentration in muscles (less than 50 pg PGE per g muscle) and increased the magnitude of contractions induced by either ACh or elevated potassium. Spontaneous contractions were observed in many tissues after inhibition of PGE synthesis. In conclusion, endogenous PGE limits spontaneous and depolarization-induced muscular activity in cat ileal circular muscle. Synthesis of PGE was increased by depolarizing stimuli whether or not contractions were blocked by the removal of external calcium.