Aging and ovarian function in the white-footed mouse (Peromyscus leucopus) with specific reference to the development of preovulatory follicles.

A study was made of the effects of increasing age on uterine histology, follicular development and steroidogenesis within the ovary of the white-footed mouse (Peromyscus leucopus). The animals were autopsied on each day of the estrous cycle and ranged from 14 to 49 mos. of age. The data indicated that the animals maintained estrous cycles throughout their lifespan as judged by cyclic changes in uterine histology. In addition these studies showed that aging (1) did not alter ovarian concentrations of testosterone, 17 beta-estradiol or progesterone, (2) resulted in a decrease in the number of primary and preantral follicles during metestrus, proestrus and estrus, (3) increased the percentage of atretic preantral follicles during metestrus only, and (4) did not reduce the number of antral (preovulatory) follicles that develop by proestrus. These observations suggest that in P. leucopus the "rescue" of preantral follicles constitutes the mechanism which compensates for the decrease in the number of smaller follicles and allows the normal number of preovulatory follicles to develop and ovulate. It is also possible that this mechanism exists in the laboratory mouse and rat since species-specific numbers of preovulatory follicles develop in aged cycling animals despite an age-related decrease in the total follicular populations.