Hemiovariectomy and follicular growth in the immature rat

Female rats were hemiovariectomized on day 1 (T2) or day 10 (T3) after birth. The population of growing follicles in the remaining ovary and the plasma levels of FSH an LH were compared to controls (T1) on post-natal days 20, 30 and 38. There was a non significant trend towards higher FSH and LH levels in hemicastrates. Hemicastration had a significant (P less than 0.05) overall effect on the number of small (1 to 2 layers of granulosa cells) and preantral follicles (more than 2 layers of granulosa cells and diffuse antrum): small follicles were more numerous (P less than 0.05) in ovaries of the T3 group, whereas preantral follicles were more numerous in the T2 group. Atresia was somewhat lower in hemicastrates compared to controls. The observed increase in the whole population of follicles, in the remaining ovary, may be attributed to several factors including a decrease in steroids and inhibin, an increase in FSH and/or a neural discharge signal. The increased number of follicles may constitute a reserve to maintain the characteristic ovulation pattern of the species in later life.