Ripening of the uterine cervix of the guinea-pig after treatment with the progesterone antagonist onapristone (ZK 98.299): an electron microscopic study.

The effects of the progesterone antagonist (AG) onapristone ZK 98.299 on the uterine cervix were investigated by electron microscopic examination in guinea-pigs during late pregnancy. Treatment with the AG led to dissolution, splitting up and dissociation of collagen fibres as well as expansion of the inter-fibrillar spaces due to oedema. This was associated with an increased number of polymorphonuclear granulocytes, macrophages and mast cells as well as with the appearance of highly active fibroblasts. The possible roles of these cells in the dissociation of collagenous fibres are discussed. Comparing the AG-induced prominent transformation of the uterine cervix with the morphological signs characteristic of cervical ripening in untreated guinea-pigs at term pregnancy, no significant differences could be observed. This suggests that AG brings about ripening and dilatation of the cervix in a physiological manner and may be, after thoughtful toxicological screening, an extremely useful agent for obstetrical indications.