Testosterone Pretreatment and the Response of Pituitary LH to Gonadotropin-Releasing Hormone (GnRH) in the Male Dog

¹ Departments of Physiology/Pharmacology, Southern Illinois University School of Medicine, Carbondale, Illinois
² Division of Statistics and Measurement, Southern Illinois University School of Medicine, Springfield, Illinois

To characterize the effects of testosterone (T) pretreatment on the response of pituitary LH secretion to exogenous gonadotropin-releasing hormone (GnRH), intact male dogs were injected subcutaneously with either oil or 500 µg/kg of T in oil at 1, 3, 6, 12, or 24 hours prior to intravenous GnRH administration (50 ng/kg). The pre-GnRH levels of plasma LH were reduced in all groups of T-treated dogs except in animals given T 1 hour before GnRH. The concentrations of plasma LH during both the peak-response period and the recovery period following GnRH administration in animals injected with T did not differ from those in animals injected with oil. These results indicate that T pretreatment has no effect on the ability of the pituitary to respond to exogenous GnRH at all time periods tested, and imply that direct feedback of T on the pituitary may not be acutely involved in steroid negative feedback in the male dog. Unexpectedly, however, there was some indication that the time of injection of either oil or T could affect the response of the pituitary to GnRH, and this may represent a stress phenomenon.

     Key words: GnRH, LH-response, testosterone, dog

Submitted on May 1, 1981
Revised on June 8, 1981
Accepted on September 24, 1981