Quantitative studies of the effect of progesterone on endometrial morphology of the spayed rat

The effects of various dosages and of various time periods of treatment with progesterone have been studied in the spayed, mature rat. Test objects were the cells of the luminal epithelium and of the endometrial stroma which were examined by qualitative and quantitative electron microscopy. No significant response was observed in epithelial or stromal cells until after 12 hrs of progesterone treatment. The nuclei of both cell types were then more circular than earlier with reduced long diameters. The functional significance of this change in configuration is unclear since only in the stromal cells was it followed by nuclear growth. Further, after 12 hrs of treatment the relative amounts of mitochondria and granular endoplasmic reticulum of stromal cells were reduced while the volume of the stromal cell cytoplasm appeared enlarged. This is taken as evidence that progesterone causes an intracellular oedema probably by decreasing cell membrane permeability. This response is probably not specific for the stroma but also includes the luminal epithelium, although the volume of the epithelial cell cytoplasm could not be determined here. Nucleolar enlargement did occur in stromal cells and was observed after 12 hrs of treatment but was not significant until after 24 hrs. At this point of time the net amount of granular endoplasmic reticulum in stromal and epithelial cells was increased indicating an increased protein synthesis in both cell types. However, only in the stromal cells was this associated with nucleolar enlargement, which supports the idea that progesterone stimulates protein synthesis through different mechanisms in the two cell types. Testing various dosages of progesterone showed that 0.5 mg had an effect similar to 5 mg of progesterone. When 0.05 mg progesterone was injected the only effect observed was an increase in the amount of apical vesicles of the luminal epithelium, showing that the epithelium is more sensitive to progesterone than the stroma.