TESTOSTERONE AND OESTRADIOL SUPPRESSION OF LH AND FSH IN ADULT MALE RATS: DURATION OF CASTRATION, DURATION OF TREATMENT AND COMBINED TREATMENT

ABSTRACT The effects of androgens and oestrogens on serum LH and FSH in castrated rats were evaluated with regard to the modifying influences of duration of castration, duration of treatment and combined oestrogen-androgen effect. Serum LH was not greatly influenced by these variables. In contrast, serum FSH was shown to be more resistant to suppression by both steroids after at least five days of castration, requiring a longer duration of treatment to be suppressed to intact levels. Combined treatment of submaximally suppressive doses of testosterone propionate and oestradiol benzoate resulted in no additive effect on lowering serum FSH. Low doses of both androgens and oestrogens resulted in elevated levels of serum LH and FSH, suggesting that the adult male hypothalamic-pituitary axis may be responsive to positive feedback. In all studies, testosterone preferentially suppressed serum LH as compared to serum FSH. In contrast, oestradiol administration produced parallel inhibition of both LH and FSH. It is emphasized that neither oestrogen nor androgen alone, nor in combination, resulted in preferential inhibition of serum FSH over LH.