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H. E. Chemes, M. A. Rivarola and C. Bergadá

Summary.

The actions of HCG and PMSG for different periods and of testosterone on the immature rat testis were studied. Short-term administration of HCG (1-3 days) induced an early meiotic and postmeiotic stimulatory effect but a decrease in spermatogonial numbers. Administration of HCG for longer periods (10 days) caused a reduction in numbers of all cell types. Treatment with HCG + PMSG reduced the amount of inhibition, while PMSG alone resulted in histological and humoral signs of stimulation of the interstitial tissue and the meiotic and postmeiotic stages; the numbers of spermatogonia were not affected. Testosterone caused stimulation of the meiotic and postmeiotic stages and a reduced number of spermatogonia. It is concluded that while PMSG directly stimulates spermatogonia, HCG acts through testosterone secretion at the meiotic and postmeiotic stages. The early inhibitory effects of HCG and testosterone on spermatogonial numbers could be ascribed to the inhibition of endogenous FSH by androgens.

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H. E. Chemes, M. A. Rivarola and C. Bergadá

Summary.

The effect on the interstitial cells in the immature rat testis of administration of HCG for different periods was correlated with testosterone plasma levels. Significant and progressive stimulation of mitosis was observed after 3 days of HCG treatment but stabilization occurred after 5 days. The numbers of precursor fibroblasts had increased by the 5th day and were still increasing by the 10th day of treatment. Numbers of Leydig cells were significantly greater at 5 and 10 days of treatment. Plasma testosterone showed a progressive and continuous increase in all groups. The increase in Leydig cell number is considered to be due to a combination of increased stimulation of mitoses in Leydig cells and differentiation of precursor fibroblasts. Mitosis seems to precede fibroblastic differentiation, but the latter continues when mitotic changes have stabilized. The elevation of plasma testosterone concentrations is probably due firstly to the stimulation of the existing Leydig cells and then to the increase in the number of hormone-secreting cells.