Metabolic clearance and production rates of human luteinizing hormone in pre- and postmenopausal women

Abstract

Metabolic clearance rates and production rates of human luteinizing hormone (HLH) were determined in pre- and postmenopausal women by the constant infusion technique. Highly purified HLH-(131)I was infused into the fasting subjects at a constant rate. Serial plasma samples were obtained and the radioactive hormone was precipitated by a double antibody technique. Plasma HLH-(131)I levels reached equilibrium by 4 hr after the infusion started. Metabolic clearance rates were: 24.4 +/- 1.8 (mean +/- SE) ml/min in five normal premenopausal women; 23.3 +/- 1.1 ml/min in five normal women taking norethinodrel and mestranol; and 25.6 +/- 4.1 ml/min in four postmenopausal women. Endogenous plasma HLH levels measured in the same subjects by radioimmunoassay immediately before infusion were 32.0 +/- 9.6 mU/ml in the normal women, 16.8 +/- 3.2 mU/ml in the women on oral contraceptives, and 99.2 +/- 23.2 mU/ml in the postmenopausal women. The corresponding HLH production rates were: 734 +/- 170 mU/min in the normal women: 387 +/- 86 mU/min in the women on norethinodrel and mestranol; and 2400 +/- 410 mU/min in the postmenopausal women. The metabolic clearance rate did not change after ovariectomy in one women, but the production rate rose from 583 to 1420 mU/min. Based on previously reported bioassay values for pituitary content and urinary excretion of HLH, the estimated turnover of HLH in the pituitary is about once per day and less than 5% of the total HLH produced appears in the urine in a biologically active form.