[Alteration of prostaglandin I2 on ripening in rabbit uterine cervix].

We have attempted to clarify the relationship between PG synthesis and ripening in rabbit uterine cervix. In this paper, I examined whether PGI2 release from endogenous arachidonic acid is changed in ripening in the uterine cervix. The release of 6-keto PGF1 alpha significantly increased after the 20th day of gestation and at term reached its maximum, which was about six times that of non-pregnant rabbits. I then measured the activity of phospholipase A2 in the tissue and found that it was significantly increased during gestation. Furthermore, to determine which cells synthesize PGI2, several kinds of cells from the uterine cervix of non-pregnant and pregnant rabbits were isolated and cultured. Among these cells, smooth muscle cells were shown to have the PGI2 synthesizing activity. The rate of conversion of arachidonic acid to PGI2 in the cell was about 30%, and that to PGE2 was negligible. To examine the change in PGI2 synthesis with gestational age, cells from both non-pregnant and from the 25th day of gestation were cultured and the release of PGI2 from these cells was determined by radioimmunoassay of 6-keto PGF1 alpha. The release of 6-keto PGF1 alpha in gestation was about three times as high as in the cells from non-pregnant rabbits.