CONTROL OF GONADOTROPHIN SECRETION BY STEROID HORMONES IN CASTRATED MALE TRANSSEXUALS. I. EFFECTS OF OESTRADIOL INFUSION ON PLASMA LEVELS OF FOLLICLE-STIMULATING HORMONE AND LUTEINIZING HORMONE

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Abstract
Twenty-four infusions of estradiol (E2) in graded doses ranging from 0-200 .mu.g administered over 7 h were carried out in 11 healthy male transsexuals who had undergone sex reassignment at least 3 mo. previously. Plasma levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and E2 were analyzed by radioimmunoassay, while sex hormone binding globulin (SHBG) was measured using 3H-testosterone as the saturating ligand. Infusion of 5-200 .mu.g of E2 raised plasma E2 to levels ranging from 38.4-367.8 pg/ml which represent 83-800% of levels found in a control group of 63 normal males. SHBG capacity remained unchanged at all doses of E2 studied. No change in plasma levels of FSH and LH was observed in control infusions and infusion of 5 .mu.g of E2. From 10-200 .mu.g, suppression of plasma levels of FSH was noted at the 5-7 h period. The suppression increased up to 20 .mu.g and thereafter the levels of FSH remained constant. The suppression of LH increased up to the highest E2 dose (200 .mu.g) studied. Significant suppression of LH occurred earlier than the 5-7 h as the dose of E2 increased. E2 plays a part in the regulation of secretion of FSH and LH in men; at doses higher than physiological, E2 exerts a differential effect on the secretion of FSH and LH.