Developing Morphological Asymmetry of Ovarian Follicular Maturation in Monkeys1

In order to study recruitment and selection of the dominant ovarian follicle in the menstrual cycle, we used luteectomy to synchronize the onset of new follicle growth. Previous experiments showed that the next ovulation after surgical removal of the corpus luteum usually occurs within approximately 14 days and is most often on the contralateral ovary. Twenty regularly cycling rhesus monkeys were luteectomized in midluteal phase and assigned to one of four groups. Ten of these monkeys were unilaterally ovariectomized 4 days after luteectomy; 5 underwent removal of the ipsilateral ovary (Day 4-I) and in 5 the contralateral ovary (Day 4-C) was excised. The remaining 10 were hemiovariectomized 8 days after luteectomy; again, 5 were hemiovariectomized on the same side as luteectomy (Day 8-I) and 5 on the contralateral aide (Day 8-C). Ovaries were serially sectioned; all antral follicles were classified and measured. Results indicate a significant increase (P<0.05) in medium size (0.5–1.0 mm) developing follicles in the Day 4-C versus the Day 4-I ovaries, even though an overt dominant follicle was not identified in either group. The next preovulatory luteinizing hormone (LH) surge occurred about 13 days after hemiovariectomy for both groups. In ovaries of the Day 8C group, there was a significant decrease (P<0.05) in medium size developing antral follicles and a significant increase in medium size early atretic follicles. Following contralateral hemiovariectomy on Day 8, the next LH surge was deferred until 18 days after luteectomy, suggesting that the new dominant follicle was removed along with the excised ovary. This is in contrast to the Day 8-I group, in which the distribution of follicles resembled that in the Day 4-I ovaries; the next LH surge was not delayed, occurring approximately 5 days after hemiovariectomy. These findings demonstrate: 1) that morphological asymmetry of certain sized developing antral follicles was detectable as early as Day 4 after luteectomy; 2) that follicle growth within the ipsilateral ovary was retarded even 8 days after luteectomy; and 3) that selection of the dominant follicle was not completed within 4 days in this experimental model, but was absolute by 8 days after luteectomy.