THE RESPONSE OF THE IMMATURE RAT OVARY TO GONADOTROPHINS: ACUTE CHANGES IN CYCLIC AMP, PROGESTERONE, TESTOSTERONE, ANDROSTENEDIONE AND OESTRADIOL AFTER TREATMENT WITH PMS OR FSH + LH

Abstract

Radioimmunoassays were used to measure changes in progesterone, testosterone, androstenedione, estradiol, gonadotropin and ovarian cyclic AMP in immature female rats during the 1st 24 h after exposure to slowly [PMS (pregnant mare serum gonadotropin)] or rapidly [follicle stimulating hormone (FSH) + luteinizing hormone (LH)] disappearing gonadotropins. Cyclic AMP was increased 30 min after injection of either kind of gonadotropin, but it 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 gonadotropin. With PMS the peak in the serum was reached at 8 h, it remined 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. Estradiol was not increased in the serum or the ovary until 20 h after PMS. One or 2 doses of FSH + LH did not produce an increase in estrogen, but a transient increase was found with 3 doses; 4 doses kept an elevated level of estradiol for 12 h. The aromatizing system of the immature rat ovary probably is relatively inactive and continual stimulation by gonadotropin for about 10-12 h is probably necessary to bring about increased function. The mechanisms for the synthesis and secretion of progesterone and androgens are very active and can be immediately stimulated by exposure to gonadotropins.