Role of the pituitary in controlling oogenesis in the rabbit.

The involvement of the pituitary and mesonephros in oogenesis was examined with the rabbit used as an experimental model. Fetal and neonatal ovaries were cultured for 8 days with and without their corresponding pituitaries or as half cranial or caudal portions. Progression of meiosis was followed histologically and autoradiographically by the uptake of tritiated thymidine. Pulse labeling for 24 h occurred on Days 0, 2, 4 and 7 of culture. No difference was noted in labeling or progression of meiosis in neonatal ovaries with or without the pituitary or in sectioned ovaries. By contrast, fetal ovaries with pituitary that were labeled on Day 4 had a labeling index (positive cells/1000 microns 2 of cortex) of 282.1 +/- 32.9 (mean +/- SEM) compared to 107.1 +/- 24.9 for ovaries without pituitary. Those labeled on Day 7 showed the same differences (263.7 +/- 46.0 vs. 160.2 +/- 20.8). Histologically, there was a threefold difference in percentage of germ cells with pituitary undergoing meiosis (21.2 +/- 2.9% compared to 7.1 +/- 2.8% without). These data suggest that the fetal pituitary has an important role in inducing meiotic prophase in the rabbit.