EVIDENCE FOR STEROIDOGENIC LUTEAL CELL HYPERTROPHY AND HYPERPLASIA DURING PREGNANCY IN THE RAT

The proliferative activity of the rat corpus luteum was studied on day s 2, 3, 6, 9, 12, 15, 17, 19 and 21 of pregnancy. proliferating cells were detected by the immunohistochemical demonstration of DNA-incorpor ated 5-bromodeoxyuridine (BrdU) and by the presence of mitoses. Steroi dogenic luteal cells showed two proliferative waves on days 12-15 and on day 21, when relatively abundant BrdU-labeled and mitotic cells wer e observed. These cells were clearly distinguishable from nonsteroidog enic cells by their round nuclei and large polygonal cytoplasm. The pr oliferative activity on days 12-15 was coincident with an increase in the size of the cells and in progesterone concentrations. On the other hand, the proliferative activity of non-steroidogenic luteal cells (e specially endothelial cells of the blood and lymphatic vessels) follow ed a different pattern. These cells intensely proliferated on days 2-3 of pregnancy and this proliferative activity was significantly higher than that observed in non-pregnant rats on metestrus and diestrus. A new proliferative wave was observed on days 12-15, in association with the increase in the proliferative activity of steroidogenic cells. Th e presence of both BrdU-labeled and mitotic steroidogenic luteal cells provides evidence that these cells do proliferate and that both hyper trophy and hyperplasia are involved in the increase in the parenchyma of the corpus luteum during pregnancy. Also, the results suggest that different mechanisms are involved in the regulation of the proliferati ve activity in the corpus luteum at different times during pregnancy.