Renal Metabolism of the β-Subunit of Human Choriogonadotropin in the Rat

We analyzed the immunoreactive renal metabolites of the β-subunit moieties of unlabeled highly purified hCG, hCGβ, and desialylated hCG (as-hCG) in rats by RIA and Sephadex G-100 chromatography. Infusions of hCGβ, as-hCG, or intact hCG resulted in accumulation in the kidney of a large quantity of small mol wt peptides lacking the immunological determinants of the carboxy-terminal peptide (CTP) of the β- subunit. In the case of as-hCG, renal accumulation of these β- core fragments was greatly enhanced when as-hCG binding to hepatic galactose receptors was inhibited by infusion of asfetuin. The β-core fragments in kidney had the same immunological and G-100 chromatographic characteristics as β-core fragments in liver, suggesting similar intracellular catabolic mechanisms in these tissues. The kinetics of β-core fragment turnover in kidney were studied after injection of hCGβ, which is cleared from the circulation within 1 h. Loss of βCTP immunoreactivity was the initial event in hCBβ catabolism by the kidne...

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