The effect of pretreatment with several sex steroids and some of their combinations was studied in intact and castrated male rats. The pretreatment of intact male rats with testosterone did not modify the FSH release but inhibited the LH release after the injection of LH-RH as compared with the oil-pretreatment control rats. Dihydrotestosterone significantly depressed LH release, but did not modify FSH release after the administration of LH-RH. This resulted in a change of the FSH/LH ratio in serum after LH-RH, as compared with the oil-treated rats. Estradiol significantly inhibited the FSH release, but augmented the LH release after administering LH-RH, also resulting in a change of the FSH/LH ratio as compared with control rats. 17-Hydroxyprogesterone and pregnandione did not modify the pituitary response to LH-RH. The combination of estradiol plus dihydrotestosterone depressed the pituitary response to LH-RH. Estradiol plus 17-α-hydroxyprogesterone slightly augmented, and estradiol plus pregnandione significantly augmented the LH release after the administration of LH-RH. In castrated male rats, dihydrotestosterone significantly depressed LH but not FSH release after the administration of LH-RH. 20-α-Dihydroprogesterone and pregnandione slightly, but not significantly, inhibited LH but not FSH release after the administration of LH-RH. The combination of estradiol plus testosterone or dihydrotestosterone significantly depressed, and the combination of estradiol with either of the two progestogens used augmented the pituitary response to LH-RH. The results indicate that sex steroids influence the response to LH-RH in vivo, and can alter the LH/FSH ratio.
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