Suppressive Action of Norethisterone Enanthate and Acetate on Gonadotropin (FSH and LH) Levels

Radioimmunoassay in Eugonadal and Postmenopausal Women

Abstract

Norethisterone derivatives (acetate and enanthate) depress serum FSH and LH levels, as determined by radioimmunoassay. In the normally menstruating woman, norethisterone acetate, administered orally in low doses, did not modify the baseline concentrations of gonadotropins but regularly inhibited the acute liberation of FSH and LH at midcycle. In the postmenopausal woman, these agents primarily decreased serum LH regardless of the derivative used, the dose level or the mode of administration. In postmenopausal women injected intramuscularly with a high dose of norethisterone enanthate (200 mg), FSH levels were also diminished, but the decrease was less rapid. less pronounced and less prolonged than the drop in LH. No statistically significant decrease in serum FSH concentrations occurred in similar subjects treated daily with low oral doses of norethisterone acetate (0.3 mg). The inhibitory effects exerted by these derivatives of 19-norethistcrone on LH levels are thus more marked than those exerted on FSH levels.