Preantral follicle development during the menstrual cycle in the Macaca mulatta ovary

Ovaries obtained from 18 adult, regularly cycling rhesus monkeys were evaluated to determine the status of preantral follicle development at various stages throughout the menstrual cycle. The ovaries were serially sectioned, and all preantral follicles on every 20th section were classified as developing or atretic, counted and/or measured, and grouped according to size. Results from this study revealed (1) that a significant increase (P less than 0.05) occurred in the mean percentage of developing preantral follicles greater than 100 microns in diameter during the periovulatory period, suggesting that follicles in this size range had developed a sensitivity to the unique hormonal milieu present during that stage of the cycle; (2) that similar numbers of primordial and developing preantral follicles were present in the right and left ovaries of a pair, showing that neither ovary had a predominance over the other; (3) that the mean number of developing preantral follicles varied directly with the size of the primordial follicle pool; (4) that atresia was minimal with no significant differences between the various stages of the cycle in any size group; and (5) that polyovular follicles were abundant in certain pairs of ovaries, but could not be related to age or stage of cycle.