SERUM LH AND FSH LEVELS FOLLOWING INTRAVENOUS INJECTION OF A GONADOTROPHIN RELEASING PRINCIPLE IN NORMAL AND GONADECTOMIZED ADULT MALE RATS TREATED WITH OESTRADIOL-17β OR 5α-DIHYDROTESTOSTERONE

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Abstract
The effect of i.v. administration of a synthetic gonadotropin releasing factor (GnRF) on circulating LH [luteinizing hormone] and FSH [follicle-stimulating hormone] concentrations was investigated in normal and gonadectomized, adult male rats injected s.c. each day during 7 days with various doses of estradiol-17.beta. or 5.alpha.-dihydrotestosterone in sesame oil. Higher increase in serum LH and FSH levels subsequent to i.v. administered GnRF was observed in castrated control animals than in intact control animals, though this increment was not of significant nature for serum FSH. Pretreatment of normal and gonadectomized rats with estradiol-17.beta. resulted in an augmented response of serum LH and FSH concentrations to GnRF i.v. Pretreatment of normal and gonadectomized rats with 5.alpha.-dihydrotestosterone diminished serum LH and FSH response following administration of the same amount of GnRF. For these steroids to affect the response pattern of serum LH and FSH to GnRF i.v. higher doses were required in normal than in gonadectomized animals. Estrogen and androgen may act at different sites in the male hypothalamic-pituitary axis with respect to regulation of pituitary gonadotropins.