Inhibition of luteinizing hormone secretion during quiescent interval of testicular androgen production in immature mice.

We reported [1] that the proliferation of seminal vesicle cells in mice takes place largely in the neonatal (days 0-15) and pubertal (days 25-35) periods and that between neonatal and pubertal proliferations, a quiescent interval of cell proliferation due to markedly diminished secretion of androgens occurs. The present study was carried out to investigate the mechanism for this quiescent interval of Leydig cell activity. Serum LH concentrations were moderate (0.29 ng NIH-LH-S1/ml) at 8 days of age, low (0.13 ng/ml) at 18 days, and high (0.78-0.60 ng/ml) at 30, 40 and 60 days. The LH level on day 18 was almost the same as that found in hypophysectomized adult mice (0.12 ng/ml). These changes with age in serum LH concentrations paralleled those for serum total androgen (testosterone plus 5 alpha-androgens) concentrations. The injection of HCG (1 IU/day) or LH releasing hormone (0.1 or 0.4 microgram/6h) for 1 or 2 days resulted in significant and marked increases on day 18 in testicular and serum androgen levels and/or the proliferation of seminal vesicle cells measured with 5-[125I]iodo-2'-deoxyuridine uptake by the whole seminal vesicles. These findings lead to the hypothesis that the quiescent interval of testicular androgen production due to inhibition of pituitary LH secretion occurs around day 20 in mice.