Morphology of the Corpus Luteum in the Sheep During Regression Induced by Prostaglandin F2

Ewes at Day 10 of the estrous cycle were infused via a uterine vein ipsilateral to the corpus luteum with prostaglandin (PGF20). The effects of this treatment on the ultrastructure of the luteal cells were examined, and the findings were related to the potency of PGF20 in effecting a reduction in the secretion of progesterone by the ovary. After a 6 h infusion of PGF20 (40ig/h) there was an abrupt decrease in the concentration of progesterone in peripheral plasma, and the fine structure of the corpus luteum showed that this change in hormonal status was accompanied by cessation of granule secretion by the luteal cells. Autophagocytic bodies could be detected in the luteal cells immediately after the infusion and lipid droplets had also begun to accumulate. Progression of these structural changes led to cellular shrinkage and disorganization culminating in regression of the corpus luteum 48 h after the infusion. It is concluded from the present work that the structural and functional features characteristic of normal luteal regression are also associated with the demise of the corpus luteum after treatment with PGF20. Both in normal and in ovarian steroid secretion was related to the densely-staining granules thought to contai