Metabolism, distribution and excretion of purified human chorionic gonadotropin and its subunits in man.

We have characterized the distribution, metabolism and excretion of hCG and its subunits in normal human subjects. The initial apparent volume of distribution was the same for hCG, hCG beta, and hCG alpha. Their disappearance curves fit a two-component exponential model, and calculations indicated that both the rapid and slow phase half-times of hCG are approximately 10-fold greater than those of hCG beta and 30-fold greater than those of hCG alpha. Despite the more rapid metabolic clearance rates of the subunits, their renal clearance is 2- to 3-fold less than that of hCG. Thus, renal clearance accounts for less than 1% of the metabolic disposal of the subunits, whereas it represents a major fraction (20-25%) of the metabolic disposal of hCG. After injection of the isolated beta subunit of hCG, two forms were excreted in the urine. One was intact hCG beta and the other was a discrete fragment of the hCG beta which appears to lack the hCG beta carboxyterminal peptide immunologic determinant; we have termed this later material an hCG beta core fragment.