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Biology of Reproduction, Vol 14, 665-669, Copyright © 1976 by Society for the Study of Reproduction

Effect of Testosterone Implants on Serum Gonadotropin Concentrations in the Male Rat

W. H. MOGER 1

1 Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7


Subcutaneous implantation of testosterone in Silastic capsules in castrated male rats results in sustained elevations of serum testosterone. In rats castrated and implanted with capsules 2cm long at 30 days of age, serum testosterone concentrations were elevated within 24 h and then gradually declined during the following nine days. This decline appears related to the animals’ growth. In rats castrated and implanted at 30 days of age with capsules ranging in length from 0.5 to 2cm, serum testosterone concentrations at autopsy 5 days after implantation were comparable to those of intact control animals of the same age. The capsules suppressed the castration induced rise in serum gonadotropin concentrations. Similar results were obtained with rats castrated and implanted with either one or two capsules 4cm long at 80 days of age.

Although these results suggest that serum testosterone concentrations in either sexually immature or mature male rats can regulate serum gonadotropin concentrations, the question arises whether the sustained release of testosterone from Silastic capsules mimics the pattern of endogenous testosterone secretion.

Note:
ACKNOWLEDGMENTS The technical assistance of Ms. V. Masland and the editorial assistance of Miss E. Shapter are gratefully acknowledged. Acknowledgment is also extended to Dr. T. Kennedy for advice on the preparation of the testosterone capsules. This work was supported by Grant MA-5401 from the Medical Research Council of Canada.

Submitted on January 15, 1976
Accepted on February 27, 1976




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Copyright © 1976 by the Society for the Study of Reproduction.