Time-course of the effect of treatment with a potent LHRH agonist on testicular steroidogenesis and gonadotropin receptor levels in the adult rat.

Abstract

Abstract The testicular steroidogenic pathway was studied by radioimmunoassay of steroid intermediates at different time intervals (up to 8 days) during daily treatment of adult male rats with 1μg of the LHRH agonist [D-Ala[su6], des-Gly-NH210]LHRH ethylamide. While testieular pregnenolone levels remained relatively stable, a transient increase of the progesterone concentration was observed up to day 2 with a return to control levels at day 4 and 8. On the other hand, 17-OH-progesterone, androstenedione and testosterone levels decreased progressively to reach 30, 5 and 15% of control, respectively at 4 days. During the same period, the testicular content of 5α-dihydrotestosterone was inhibited to only 40–60% of control while concentrations of 17β-estradiol and estrone remained unchanged. Changes of plasma progesterone, testosterone and estradiol concentration were parallel to those of testicular steroid content. Testicular LH and prolactin receptor levels were rapidly and markedly decreased after treatment with the LHRH agonist while FSH receptor levels remained unchanged. The present data show that the loss of testicular LH and prolactin receptors induced by treatment with an LHRH agonist is accompanied by marked changes of the steroidogenic pathway, the defects being possibly located at the level of the 17-hydroxylase and 17,20-desmolase. Since 17β-estradiol levels remain unchanged during treatment, it is likely that the estrogens are not involved in testicular desensitization.