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Effects of prostaglandins E1 and E2 on the mechanical activity of isolated circular and longitudinal muscle strips of guinea-pig stomach.

Small muscle strips isolated in longitudinal and circular direction from the fundus, corpus and antrum as well as from the pyloric sphincter of the guinea-pig stomach were mounted in an organ bath for recording their spontaneous contractility. Concentrations of the order of 10(-10) to 10(-7)M of prostaglandins E1 and E2 (PGE) were tested and compared with the effect of acetylcholine (ACh). Acetylcholine (10(-7) to 10(-5)M) was found to be a universal activator of all muscle strips. PGE1 and PGE2 induced a dose-dependent tonic activation of the longitudinal strips from the fundus, corpus and antrum. In circular muscle strips from the same regions PGE1 and PGE2 induced negligible tonic activation at concentrations of 10(-10) to 10(-8)M and strong inhibition at concentrations above 10(-8)M. PGE1 and PGE2 inhibited in a dose-dependent manner the phasic contractions of circular muscle strips from corpus, antrum and pyloric sphincter. These effects of PGEs appeared in the presence of adrenergic and cholinerigc blocking agents as well as of tetrodotoxin (TTX) and were myogenic in nature.