Renal Clearance Rates of the Subunits of Human Chorionic Gonadotropin in Man

Publisher Website
Google Scholar
Abstract
The excretion of hCGα and hCGβ in the urine of normal subjects was measured after iv administration of 1.0 mg of the highly purified subunit preparations. By 4 h after injection, most of hCGα and hCGβ had disappeared from the serum; therefore, levels of the subunits were measured in the urine collected over this 4-h period. Greater than 90‥ of the excreted immunoreactive (IR) hCGβ measured in the urine was identical to the authentic purified hCGβ based on the following criteria. 1) It dosed out parallel to authentic hCGβ in the RIA for hCGβ. 2) It exhibited the unique carboxy-terminal peptide immunological determinant of hCGβ. 3) Its apparent molecular weight, determined by Sephadex G-100 chromatography, was identical to that of hCGβ. 4) It adsorbed to Concanavalin A. Similarly, most of the IR hCGα a excreted in the urine after the injection of hCGα was judged to be authentic hCGα a based on the criteria of identical molecular weight by gel chromatography, dilution parallel to authentic hCGα in the homologous RIA, ami adsorption to Concanavalin A. During the 4-h collection period, the quantity of IR hCGα excreted in the urine was 3144 ± 346 ng (mean ± SE; n = 7), and the quantity of IR hCGβ was 5042 ± 811 ng (mean ± SE; n = 13). The renal clearance rate (RCR) was calculated based on the serum concentration of the subunitsduring the 4 h in which urine was collected. The RCR of hCGα (0.164 ± 0.019 ml/ min-m2) was not significantly different from that of hCGα (0.130 ± 0.020 ml/ min-m2). The ratio of RCR to MCR was 0.0033 for hCGα and 0.0068 for hCGβ (P < 0.01), the difference being due to the substantially lower MCR of hCGβ. We conclude that urinary excretion as unaltered subunit accounts for a very small fraction of the total metabolic fate of the hCG subunits in man.