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Journal of Andrology, Vol 3, Issue 5 297-304, Copyright © 1982 by The American Society of Andrology

Temporal Dissociation of Feedback and Direct Testicular Effects of Estradiol Benzoate in Male Rats

H. EDWARD GROTJAN Jr. 1 AND EMIL STEINBERGER 1

1 Department of Reproductive Medicine and Biology, University of Texas Medical School at Houston, Houston, Texas

Studies were conducted to characterize the responses of the hypothalamic-pituitary-testicular axis to systemic injection of estradiol benzoate (EB) in the rat. Feedback effects of estrogens on the hypothalamic-pituitary axis were assessed by changes in serum concentrations of LH whereas testicular androgen production was examined by in vitro testicular incubations in the presence and absence of 160 mIU hCG/2.2 ml. Injection of 50 µg EB reduced serum LH and serum testosterone to low levels by 2 hours and they remained low for up to 24 hours. One to 12 hours after EB treatment, testes were as responsive to hCG in vitro as were testes from rats receiving the vehicle. However, by 16 hours after EB injection, testicular responsiveness to hCG in vitro was reduced approximately 50%. Responses to chronic EB-treatment (50 µg EB/d for 1 to 7 days) were characterized in mature hypophysectomized males. Testicular incubates from hypophysectomized EB-treated males contained less testosterone than those from corresponding oil-treated control groups. In addition, testes of hypophysectomized EB-treated males were less responsive (sim50%) to hCG in vitro, suggesting a direct effect of estrogens mediated at the testicular level. Thus, injection of estrogens to intact males reduces serum LH which, in turn, rapidly reduces serum and testicular testosterone. By 16 hours after injection, estrogens may also exert a direct effect on the testis to decrease testicular responsiveness to hCG/LH. Thus, there is a temporal dissociation of feedback and possible direct testicular effects in EB-treated males, both of which act to inhibit steroidogenesis. The reduction in LH occurs approximately 14 to 22 hours before the direct effect of estrogens on the testis is evident.

     Key words: estradiol, negative feedback, direct testicular effects, testicular incubations

Submitted on November 2, 1981
Revised on January 19, 1982
Accepted on January 19, 1982






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Copyright © 1982 by The American Society of Andrology.