Biology of Reproduction, Vol 21, 455-463, Copyright © 1979 by Society for the Study of Reproduction

Interactions of Testosterone and Estradiol-17 on the Reproductive Tract of the Male Rat

¹ Department of Pharmacology and Therapeutics and of Obstetrics and Gynecology, McGill University and the Royal Victoria Hospital, Montreal, H3G 1Y6 Canada
² Division of Reproductive Biology, Department of Population Dynamics, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Maryland 21205
³ Institute of Reproductive Biology, Department of Zoology, The University of Texas at Austin, Austin, Texas 78712

The effects of subcutaneous sustained-release implants of testosterone and estradiol-17, given either alone or in combination to adult male rats, on the weights of testis and sex accessory tissues, the testicular content of spermatids and spermatozoa and the serum concentrations of testosterone, estradiol-17 and gonadotropins were investigated. Increasing amounts of testosterone, in the absence of added estradiol, caused a biphasic response (decline followed by a partial recovery) in testicular weight and in the number of spermatids and spermatozoa/testis. Serum testosterone initially remained unchanged and subsequently rose. This pattern was reflected by the weights of sex accessory tissues. Before serum testosterone rose, serum LH decreased to undetectable levels. Serum estradiol-17 levels were not affected by increasing doses of testosterone. Low doses of estradiol-17 (0.1 cm and 0.3 cm implants), in the absence of added testosterone, had no significant effect on serum estradiol-17 levels, on testicular weights or on the testicular content of spermatids and spermatozoa, but did cause a fall in serum LH and testosterone levels and in the weights of sex accessory tissues. Higher doses of estradiol-17 resulted in increased serum estradiol-17 levels and either a decrease or a sustained low level for all other measured parameters (weights of testes and sex accessory tissues and testicular content of spermatozoa and spermatids). Depending on the doses, the combinations of testosterone and estradiol-17 resulted in 2 types of interaction: 1) at low doses, these 2 steroids acted synergistically to decrease testicular content of spermatids and spermatozoa and testicular weights but had little or no effect on serum testosterone and estradiol-17 or weights of sex accessory tissues; 2) at higher doses, there was an apparent direct antagonism between these 2 compounds on all tissue components measured.

Note:
ACKNOWLEDGMENTS This work was supported in part by NICHHD (Fellowship 00370, Research grants HD-07204, HD-03803 and A-119300 and contract 3-2745) and in part by the Medical Research Council of Canada and by the Fraser Memorial Fund of the Royal Victoria Hospital. B. Robaire is the recipient of a Scholarship from MRC of Canada. The technical assistance of N. Ruiz-Bravo, D. W. Carroll, N. Rugg, G. Zeller and B. Higginbottom is gratefully acknowledged. Reagents used to measure serum LH and FSH were provided through the courtesy of NIAMDD, Rat Pituitary Hormone Distribution Program.

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