Progesterone alters the pituitary response to luteinizing hormone releasing hormone in postmenopausal women previously treated with estradiol

Abstract

The effect of luteinizing hormone-releasing hormone (LHRH) on LH release was studied in 5 menopausal women injected with progesterone. Each patient received 2 × 100 μg doses of LHRH administered intravenously 120 minutes apart under the following conditions: without any previous treatment (test 1); 16 hours after intramuscular injection of 10 mg progesterone (test 2); after 3–4 weeks of oral treatment with 50 μg/day of ethinyl estradiol (EE₂) (test 3); 16 hours after intramuscular injection of 10 mg progesterone following treatment with 50 μg/day oral EE₂ for 3–4 weeks (test 4). The interval between tests was at least 1 month.

Progesterone decreased the total plasma hormonal increment (PHI_t) of hypogonadal women, with a reduction in plasma hormonal increment both after the 1st stimulus (PHI₁) and after the 2nd stimulus (PHI₂), whereas estradiol increased PHI_t, mainly due to an increase of PHI₂. The administration of progesterone to hypogonadal women previously treated with EE₂ maintained the increased PHI_t caused by the latter, but not owing to a greater increase in PHI₁.