[A basic study of the oxytocic effect of prostacyclin on the uterine muscle in pregnant rats].

The effects of prostacyclin (PGI2) on the uterine muscle of pregnant rats were studied in terms of uterine contraction and the variation in cyclic nucleotides. The following results were obtained: The administration of PGI2 stimulated the pregnant uterine muscle (in vitro). The oxytocic potency of PGE1-analog (ONO-802) was greatest, followed in order by that of PGF2 alpha and PGI2. The effect of 5-lypoxygenase inhibitor (AA-861) on uterine contraction was greatest under the administration of LTC4, followed in order by PGI2, oxytocin, PGF2 alpha, LTD4 and ONO-802. The effect of AA-861 was greater under the simultaneous administration of LTD4/LTC4 and ONO-802 than under the simultaneous administration of oxytocin and ONO-802. Terbutaline exerted the inhibitory effect on each of the oxytocies within two minutes in all cases. Its inhibitory effect on the oxytocics was slight in the cases to which oxytocin or ONO-802 was administered. Changes in cyclic nucleotides in the bath medium were determined before and after the administration of each drug. When PGI2 was administered, both c-AMP and c-GMP increased and showed a pattern which was different from that for other oxytocics. This tendency was also observed when PGI2 and other drugs (terbutaline, ONO-802 and AA-861) were administered together.