EFFECTS OF PROSTAGLANDINS ON ELECTRICAL AND MECHANICAL ACTIVITIES OF THE GUINEA PIG STOMACH

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Abstract
Effects of prostaglandin E1, E2 and F2.alpha. (PGE1, PGE2 and PGF2.alpha.) on electrical and mechanical properties of the smooth muscle of various areas of the guinea pig stomach were investigated. PGE1 and PGE2 (10-9-10-6 g/ml) suppressed the spontaneously generated mechanical activity in circular muscle of the pylorus but increased the activity of muscles in other areas of the stomach, while PGF2.alpha. (10-9-10-6 g/ml) showed excitatory action on muscles in all the areas of the stomach. These PG actions on the stomach muscle were mainly myogenic responses and were not affected in the presence of tetrodotoxin (10-7 g/ml). PGE1 and PGE2 (10-8-10-6 g/ml) hyperpolarized the membrane and suppressed the generation of slow potential change in the circular muscle of the pylorus, causing the cessation of spikes which were superimposed on the slow potential change. These agents depolarized the membrane and increased membrane activity in the longitudinal muscle of the pylorus and both layers of the corpus. When voltage-current relationships were observed before and during application of PG in the circular muscle of the pylorus, PGE1 and PGE2 consistently reduced membrane resistance at any given membrane potential level when compared with that in Krebs solution. In other regions of the stomach, PGE1 and PGE2 depolarized the membrane and reduced the membrane resistance at any given membrane potential level. The differences of PG action on the various regions of stomach were compared with those observed in the other visceral smooth muscles.