Quantitative analysis of oestrogen induced morphological changes in the rabbit corpus luteum

Although oestradiol is luteotropic in the rabbit, the mechanism through which oestradiol maintains the corpus luteum is unknown. To determine if ultrastructural changes in the rabbit corpus luteum accompany oestradiol treatment, corpora lutea were removed on day 10 of pseudopregnancy from hysterectomized rabbits treated with oestradiol implants and prepared for electron microscopy. Morphometric analysis was performed on luteal cells in each group (seven animals/group, four micrographs/animal) and organelle profile volumes, estimated by point-counting techniques, were expressed as a percentage of the cell volume. Morphometric analysis revealed no significant differences in nuclear, mitochondrial, lysosomal, Golgi or endoplasmic reticular volumes between control and oestradiol-treated animals. In contrast, lipid droplet volume was significantly elevated (p less than 0.001) in oestradiol-treated animals. This data suggests that an important function of oestradiol in the rabbit corpus luteum is to regulate the uptake and storage of cholesterol presumably for progesterone production.