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

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Abstract
The effects of endogenous prostaglandin E (PGE) on the contractile activity is 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 K caused contractions and enhanced PGE concentration. Removing Ca2+ from high K solutions blocked contraction, but PGE concentration still increased. The prostaglandin synthetase inhibitors, indomethacin and 5,8,11,14-eicosatetraenoic acid (ETA) reduced PGE concentration in muscles (< 50 pg PGE/g muscle) and increased the magnitude of contractions induced by either ACh or elevated K. Spontaneous contractions were observed in many tissues after inhibition of PGE synthesis. Endogenous PGE limited 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 Ca.

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