Follicular recruitment in long-term hemicastrate rats

In the long-term hemicastrate rat, the total number of ova shed during estrus is the same as in the intact rat. To determine if the dynamics of follicular development are the same in the hemicastrate rat as in the intact control rat, the remaining ovary was removed from rats 20 to 30 days after hemiovariectomy. Complete serial sections of each ovary were prepared for histological examination. All follicles greater than or equal to 300 micrometers were counted, measured, and examined for signs of atresia. Long-term hemicastrate rats had a total complement of half as many healthy antral follicles compared to intact rats at estrus. At metestrus, there were half as many small and medium antral follicles in long-term hemicastrates as in controls. However, the total number of large antral follicles was the same in hemicastrate and intact rats. Thus, by metestrus, the appropriate number of follicles for ovulation appears to have been achieved in both animals, with all these large antral follicles located in the one remaining ovary of the hemicastrate rat, while they are distributed between both ovaries of the intact rat. Ovaries of the long-term hemicastrate rats contained far fewer attretic follicles than ovaries of intact rats. These findings suggest that the process of follicular recruitment differs greatly between intact and long-term hemicastrate rats. Atresia of small and medium antral follicles (300-400 micrometers in diameter) is apparently a necessary step in achieving the correct number of ovulatory follicles in the intact rat, yet the hemicastrate rat arrives at the correct number of ovulatory follicles without atresia.