Metabolic clearance rates of the subunits of human chorionic gonadotropin in man

Abstract

Highly purified preparations of the α- and β- subunits of hCG (hCGa and hCG/S) were injected iv in normal subjects. After rapid injection, the disappearance of both subunits from serum was nonlinear when plotted on a semilog graph. A two-component exponential curve was fitted for each subject, and the curve parameters were used to estimate the MCR, apparent initial volume of distribution (Vd), and half-times of disappearance of the rapid and slow phase for each subunit. The Vd of hCGβ was indistinguishable from that of hCGα (1958 ± 131 vs. 1729 ± 99 ml/m2, respectively). The rapid phase halftime for hCGβ was significantly longer than that of hCGα (41.2 ± 1.7 vs. 13.0 ± 0.9 min; P < 0.001), and the slow phase half-time of hCGβ was also significantly longer than that of hCGα (236 ± 41 vs. 76 ± 19 min; P < 0.01). The estimated MCR of hCGα was 49.7 ± 1.6 ml/min-m2; this value was significantly greater than that of hCGβ (19.0 ± 0.7 ml/min-m2; P < 0.001). No significant differences between sexes in parameters determined for the subunits were observed. Continuous infusion of subunits at a rate of 2.7 μg/min achieved a steady state blood level of hCGβ that was significantly greater than that of hCGα (59.1 ± 7.8 vs. 24.4 ± 0.7 ng/ml; P < 0.02) and gave a MCR of hCGa that was 3 times greater than the MCR of hCGβ (72.2 ± 4.9 vs. 21.6 ± 2.8 ml/min-m2; P < 0.001). We conclude that the hCG subunits have similar Vds, but since hCGα has much shorter half-times of disappearance in both rapid and slow phases, the MCR of hCGα is much greater than that of hCGβ. © 1979 by The Endocrine Society.