Ovariectomy of rats at a young age prevents the age-related loss of neuroendocrine function. These results may suggest that the repeated, large increases in E2 secretion during successive estrous cycles eventually render the hypothalamic-pituitary axis unresponsive to further positive feedback action of E2 on LH secretion. Thus, repeated treatments with P4 implants may act to preserve a normal positive feedback response by reducing circulating E2 levels. In consonance with this view, concomitant treatments with E2 implants significantly counteract the beneficial effects of P4 implants on reproductive aging. buy asthma inhaler
In addition to the pattern of steroid exposure, the size of the ovarian follicular reserve has been shown to influence the progression of reproductive aging. Experimental reduction of the follicular reserve by unilateral ovariectomy advances the loss of regular cyclicity and fertility in rodent species. In addition, food restriction delays the onset of reproductive aging and is associated with a delayed loss of primordial follicles from the ovaries. While the mechanisms regulating the rate of follicular recruitment and depletion are not understood, it is possible that the influences of repeated P4 implant treatments on reproductive aging are associated with changes in the rate of follicular loss. To examine such a possibility, the present study was undertaken to reveal the effects of successive P4 implant treatments on age-related changes in the ovarian follicular reserve and subsequent estrous cyclicity.