Morphologic studies suggest that the proliferative activity of the ovarian surface epithelium (OSE) may vary during the reproductive life cycle. To further investigate this phenomenon, rabbit ovaries obtained before and after induction of ovulation with human chorionic gonadotropin (hCG) were incubated in medium containing 3H-methylthymidine and processed for autoradiography. Before ovulation, the labeling index (LI) of OSE cells varied from 0.04% to 0.22%. Twelve hours after hCG, the maximal LI (9.02 +/- 0.38%) was seen in OSE cells adjacent to the ovulatory stigma. The LI remained elevated at Days 1 and 5 post-hCG in OSE cells overlying corpora lutea. At Day 12, numerous papillary processes were observed at the apex of each corpus luteum. The maximal LI (16.44 +/- 1.31%) had now shifted to the OSE cells covering these processes. Eighteen days after hCG stimulation, the LI of OSE cells near the corpora lutea had returned to preovulatory levels. A slight increase in the LI of OSE cells not associated with ovulatory sites was also observed after ovulation. This study shows that a significant fraction of OSE cells undergoes DNA synthesis throughout most of the postovulatory period.

Throughout life, the ovarian surface epithelium (OSE) undergoes morphogenetic changes that may be hormonally regulated. To investigate this possibility, a population of cells morphologically identical to native OSE cells was isolated from estrous rabbits with collagenase, unit gravity sedimentation, and trypsin-EDTA. Cells were incubated with various concentrations of protein hormones in serum-rich medium or in a chemically defined medium containing fibronectin. Tritiated thymidine was added 24 h before interruption of cultures. Growth-promoting effects of tested hormones were more pronounced and consistent in serum-free cultures. Under these conditions, human chorionic gonadotropin (10,000 mIU/ml) caused a 2.8-fold increase in cell number and a 3.4-fold stimulation of thymidine incorporation. Luteinizing hormone (NIAMDD-oLH-24, 1.0 micrograms/ml) and follicle-stimulating hormone (NIADDK-oFSH-16, 1.0 micrograms/ml) produced, respectively, a 1.7-fold and 1.5-fold increase in cell proliferation, and over 1.4-fold and 1.3-fold stimulations of thymidine uptake. When used together, no growth stimulation by these gonadotropins was seen. Slight but significant increases in cell number (1.4-fold) and in radiolabel incorporation (1.3-fold) were observed with prolactin (NIADDK-oPrl-16, 10 ng/ml). These data indicate that some protein hormones promote the growth of OSE cells. This property may be important in regulating these cells during normal and pathologic states.

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