In the female rat, the ability to maintain regular estrous cycles and fertility decreases with age. Beginning at 10-12 mo, many multiparous rats display prolonged, irregular cycles or enter the anovulatory persistent-estrous state. There is also a marked decrease in the incidence of fertility with age, and litter sizes are diminished. While the detailed mechanisms responsible for the age-related reproductive decline are not completely clear, the loss of regular cyclicity is associated with alterations in the neuroendocrine regulation of gonadotropin secretion and with an age-related decline in the ovarian follicular reserve. buy ortho tri-cyclen online
Previous studies indicate that the progression of reproductive aging may be modulated by the pattern of exposure to ovarian steroids. The cessation of regular estrous cycles occurs significantly earlier in life in virgin rats than in multiparous females. In addition, our previous studies have shown that successive treatments of young virgin rats with progesterone (P4) implants decrease estradiol (E2) secretion and result in the extended maintenance of regular estrous cycles and fertility.