Changes in follicular fluid concentrations of steroids, the pattern of steroid secretion and aromatization capability of incubated preovulatory follicular wall of rats

Female Wistar rats exhibiting a regular 4-day oestrous cycle were included in this study. They were killed on the day of pro-oestrus at 11.00, 14.00, 16.00, 2.00, 22.00 and 24.00 h. The isolated preovulatory follicles were placed individually on a small triple disc of filter paper. They were cut in half and the flowing out follicular fluid (FF) was allowed to soak into the underlying filter paper disc, which was subsequently placed at the bottom of incubation chamber. It was rinsed with the incubation medium and this medium, containing FF, was collected. The remaining follicular wall was incubated for 3h. Some of the incubation media were supplemented with testosterone (T). The steroid content was estimated by radioimmunoassay. The secretion of estradiol (E) by follicular wall was high until 20.00 h while that of androgens until 22.00 h, and both declined thereafter. Relatively low progesterone (P) release rose sharply at 22.00 h and this hormone became the main steroid secreted at 24.00 h. The addition of T always enhanced the release of estradiol. Follicular fluid contained very little estradiol, while prevailing steroids were androgens. Decrease of androgen concentrations was found only at 24.00 h. Progesterone level, much lower than that of androgens, started to rise at 20.00 h and P was the main steroid present in FF at 24.00 h. The present results suggest an existence of selective passage of steroids into FF and show a presence of androgenic milieu surrounding cumulus oophorus in preovulatory FF. The results also indicate that the aromatase activity is sustained until ovulation and stress the role of the P rise observed in the secretion rate of follicular wall and FF content just before ovulation.