Effect of injection of gonadotrophin-releasing hormone on testicular steroidogenesis in the hypogonadal (hpg) mouse

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Abstract
Hypogonadal (hpg) mice were injected once daily with 10 ng, 50 ng or 1 .mu.g GnRH for 5, 10 or 20 days for 12 times daily with 4.2 ng GnRH for 5 days. Basal and hCG-stimulated production in vitro of androstenedione, testosterone and 5.alpha.-androstane-3.alpha.,17.beta.-diol(androstanediol) were measured by radioimmunoassay. All doses of GnRH increased testicular weight and in-vitro androgen production although seminal vesicle weights were unchanged and serum testosterone concentrations remained undetectable. After 5 days'' treatment androstenedione and androstanediol were the dominant androgens produced, the latter indicating the presence of high levels of 5.alpha.-reductase. By 20 days testosterone production was predominant after treatment with higher doses of GnRH. Total androgen production (androstenedione + testosterone + androstanediol) after 5 and 10 days was similar at all concentrations of GnRH used. After 20 days'' treatment total androgen production was significantly greater with 50 ng GnRN/day than with 10 or 1000 ng/day. Multiple daily injections of 4.2 ng GnRH (total dose 50 ng/day) had no greater effect on androgen production in vitro compared to single daily injections of 50 ng. This suggests that under the conditions used in this study the testis does not require pulsatile release of the gonadotrophins. The pattern of [3H]pregnenolone metabolism was measured after 5 days injection of 50 ng GnRH/day. Compared to control hpg animals there was a significant increase in formation of C19 steroids, synthesis being solely through the 4-ene pathway. These results show that GnRH treatment of hpg mice will induce testicular steroidogenesis. The changes which occur after GnRH treatment show similarities to those in the normal animal around puberty.