The onset of reproductive senescence in middle-aged female rats is associated with altered neuroendocrine regulation of gonadotropin secretion as well as changes in ovarian function. While it is difficult to determine whether neuroendocrine or ovarian impairments are primary causes of reproductive senescence, the findings from the present study indicate that the protective effect of successive P4 implant treatments on the loss of estrous cyclicity during aging is associated with a delayed depletion of follicles from the ovarian reserve. In addition, these findings may provide the basis for further study of the endocrine mechanisms regulating the rate of follicular recruitment and depletion. buy levaquin online
In the female rat, as in the human, there is an age-related decline in the ovarian follicular reserve. Several studies indicate that experimental reduction of the ovarian follicular reserve, such as that achieved by unilateral ovariectomy, accelerates the onset of reproductive aging in the rat. Similarly, the loss of regular cyclicity in middle-aged mice appears to be related to diminished numbers of resting follicles in the ovary. Middle-aged cyclic rats display reduced numbers of developing follicles during the estrous cycle, although the mean diameter and estradiol content of these developing follicles are greater than in young animals.