Preovulatory dynamics of Steroids Demonstrated in vivo by Ovarian Follicles of Cyclic and Superovulated Rat Females.
The destiny of individual follicles, especially their growth and atresia, appears to be directly related to particular steps of steroid metabolism. Since the superovulatory treatment results in insufficiently documented changes in follicular steroid levels, it was decided to search for detailed profiles of these steroids and then to compare them with these of regularly cycling females. Thus, the preovulatory follicles were isolated from superovulated immature and intact mature female Wistar rats. Mature females with regular 4-day estrous cycle were sacrificed consecutively every 2 or 3 h on the day of pro-estrus. Immature (24 day old) females were injected with PMSG (30 IU) and 56 h later with hCG (20 IU) and sacrificed at 0, 24, 48 and 56 h, and then every 2 or 3 h until 72 h after the PMSG treatment. In both animal models isolated follicles were homogenized and then the concentration of estradiol, androgen and progesterone was estimated by RIA. The follicles of cycling and PMSG/hCG injected rats showed different dynamics of steroid contents. Nevertheless, in both models a peak of androgen content appeared a few hours earlier than that of progesterone. During the progesterone peak or immediately after that a sharp fall in androgen content was found which was followed by a decrease in estradiol concentration. The follicles of superovulated rats contained lower amounts of estradiol, progesterone and especially of androgens which were much lower than these in the follicles of cyclic rats. In PMSG/hCG-derived preovulatory follicles the predominance of androgens over estradiol was maintained longer than in the follicles developing during physiological estrous cycle. These results suggest that the PMSG/hCG model of superovulation is marked by the induction of massive follicular atresia. Therefore, neither morphological nor biochemical alterations observed in PMSG/hCG-derived ovarian follicles should be considered as fully physiological changes.
Kajta
M
Laboratory of Animal Endocrinology and Tissue Culture, Department of Animal Physiology, Institute of Zoology, Jagiellonian University, 6 Ingardena Street, 30-060 Cracow, Poland.