Morphology of the Corpus Luteum in the Sheep During Regression Induced by Prostaglandin F2α

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Abstract
Ewes at Day 10 of the estrous cycle were infused via a uterine vein ipsilateral to the corpus luteum with prostaglandin (PGF2.alpha.). The effects of this treatment on the ultrastructure of the luteal cells were examined, and the findings were related to the potency of PGF2.alpha. in effecting a reduction in the secretion of progesterone by the ovary. After a 6 h infusion of PGF2.alpha. (40 .mu.g/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. The structural and functional features characteristic of normal luteal regression are also associated with the demise of the corpus luteum after treatment with PGF2.alpha.. Both in normal and in PG-induced regression the decline in ovarian steroid secretion was related to the diminished secretion by the luteal cells of densely-staining granules thought to contain progesterone.

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