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

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 ¹³¹I to specific activities of 50-150 μc/μg was used as a tracer. Both double antibody and trichloroacetic acid (TCA) precipitation techniques were used to determine HFSH-¹³¹I 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-¹³¹I 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-¹²⁵I and HLH-¹³¹I 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-¹³¹I, 8-29% was recovered in urine over 24 hr.

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