Testosterone stimulates pituitary and serum FSH in GnRH antagonist-suppressed rats

Thirty days of continuous treatment of adult male rats with 35 micrograms/day of the potent GnRH antagonist, (N-Ac-D-Nal (2)1, D-pCl-Phe2, D-Trp3, D-hArg (Et2)6, D-Ala10)-GnRH (RS-68439) reduced serum FSH to values below the limit of detection of the assay. Testosterone supplementation in the form of subcutaneous testosterone-filled silastic capsule implants present during an additional 30 days of GnRH antagonist administration restored serum FSH to values comparable to those observed after vehicle treatment. Pituitary FSH content, which was substantially reduced after GnRH antagonist treatment, was completely restored after concurrent testosterone supplementation. These results show that, under conditions of GnRH receptor blockade, testosterone is capable of stimulating pituitary and serum FSH in adult male rats.