Production rates and metabolic clearance rates of human follicle-stimulating hormone in premenopausal and postmenopausal women.

Abstract

The production rates (PR) and the metabolic clearance rates (MCR) of human follicle-stimulating hormone (HFSH) were determined in six pre- and five postmenopausal women. Human FSH (PER-780) labeled with (131)I to specific activities of 50-150 muc/mug was used as a tracer. Both double antibody and trichloroacetic acid (TCA) precipitation techniques were used to determine HFSH-(131)I levels in infusate and plasma. In four of the subjects MCRs measured by both constant infusion and single injection techniques were the same. By constant infusion, plasma HFSH-(131)I levels reached equilibrium between 4-5 hr.MCRs in six premenopausal women were 14.2+/-1.1 (mean +/-SE) ml/min. MCRs in five postmenopausal women were 12.6 +/-1.1 ml/min. Simultaneous HFSH and human luteinizing hormone (HLH) MCRs were determined in a single patient using HFSH-(125)I and HLH-(131)I as tracers by both constant infusion and single injection methods. These studies showed that the MCR of HFSH was 10.8-11.1 ml/min, and the MCR of HLH was 18.5-19.4 ml/min. From these data and previous MCR and PR studies of HLH from this laboratory, it appears that the MCR of HFSH is about one-half that of HLH. Endogenous HFSH and HLH levels were measured by radioimmunoassay. The PRs of HFSH, calculated by the product of endogenous level and MCR, were 146 +/-27mU/min in the premenopausal women and 2141 +/-264 mM/min in the postmenopausal women. 24-hr PRs, based on these results, compared with reports of 24-hr urinary excretions of biologically active HFSH indicate that 3-5% of production is found in urine in biologically active form. After our single injections of HFSH-(131)I, 8-29% was recovered in urine over 24 hr.