The response of the immature rat ovary to gonadotrophins: acute changes in cyclic AMP, progesteron, testosteron, androstenedione and oestradiol after treatment with PMS or FSH + LH.

Radioimmunoassays were used to measure changes in progesterone, testosterone, androstenedione, oestradiol, gonadotrophin and ovarian cyclic AMP in immature female rats during the first 24 h after exposure to slowly (PMS) or rapidly (FSH + LH) disappearing gonadotrophins. Cyclic AMP was increased 30 min after injection of either kind of gonadotrophin but it had returned to control level within 4 h. Serum and ovarian testosterone and androstenedione also increased to a peak at 30 min but decreased to base line by the 4th h. Multiple injections of FSH + LH maintained an elevated serum testosterone level but they had little effect upon the secretion of androstenedione. Serum and ovarian progesterone increased quickly after treatment with gonadotrophin. With PMS the peak in the serum was reached at 8 h, it remained high for 4 h and then fell precipitously between the 12th and 16th h. FSH + LH produced a prompt increase in serum progesterone but the level could be maintained only by repeated doses given every 4 h. Oestradiol was not increased in the serum or the ovot produce an increase in oestrogen but a transient increase was found with 3 doses; 4 doses kept an elevated level of oestradiol for 12 h. These results indicate that the aromatizing system of the immature rat ovary is relatively inactive and that continual stimulation by gonadotrophin for about 10-12 h is necessary to bring about increased function. In contrast, the mechanisms for the synthesis and secretion of progesterone and androgens are vary active and can be immediately stimulated by exposure to gonadotrophins.