Relaxin action on myometrial contractility

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As pilot experiments during the first year of grant-in-aid (Heisei 2), the longitudinal and circular muscle strips were separately isolated from uteri of pregnant (17-22 day), and spayed and estrogen-primed (1-3 days after estradiol 17beta injection) rats. The muscle strips were exposed to artificial saline media (Krebs composition) at 36 ﾟC, and mechanical, electrical activities, and changes in cyclic AMP content in response to porcine relaxin were examined. Porcine relaxin was provided from NIH, USA.Relaxin (50-150mU) was nearly ineffective in causing contractile depression in the longitudifnal muscle taken from uteri on 17 pregnant day. The contraction of the circular muscle was slightly depressed by relaxin, and the contractile depression was potentiated in the presence of external Mg ions. This observation is compatible with the finding that relaxin receptor dominates the circular muscle layer and it attains its peak on 17 pregnant day (Mercado-Simmen 1980, 1982).In both the longitudinal and circular muscles of estrogen-primed rats, relaxin was very effective in causing a contractile depression even in the absense of external Mg. Therefore, in the following year (Heisei 3), experiments were focussed on the above specimen.At the same time, the electrical measurements on single isolated cell of pregnant rat myometrium by collagenase treatment were challenged. The plateau potential was recorded only from a batch consisted of 5-6 cells. The interface attachment and patch clamp version 55 (Compac) purchased by the grant-in-aid, was used for this purpose.