Evidence for a gonadotropin from nonpregnant subjects that has physical, immunological, and biological similarities to human chorionic gonadotropin.

Abstract

Substances from urinary extracts of normal, nonpregnant subjects and human pituitary gonadotropin preparations reacted similarly to human chorionic gonadotropin (hCG) in a radioimmunoassay system that is highly specific for hCG and without crossreactivity to human luteinizing hormone (hLH). The antiserum was produced in a rabbit immunized with a bovine albumin conjugate of the unique carboxyl-terminal peptide (residues 123-145) isolated from a tryptic digest of the reduced, S-carboxymethylated hCG.beta. subunit. The antibody recognition site on the peptide resided on the last 15 amino acid residues of the carboxyl-terminal peptide, as evidenced by the competitive binding activities against 125I-labeled hCG of a series of peptides chemically synthesized according to the carboxyl-terminal sequence of HCG.beta.. In order to elucidate the nature of the crossreacting substance in urinary extracts, a human postmenopausal urinary preparation (Pergonal) and a kaolin-acetone extract of urine from a patient with Klinefelter''s syndrome were subjected to gel chromatography on Sephadex G-100. Fractions showing immunocrossreactivity with the antiserum to hCG.beta.-carboxyl-terminal peptide apparently coeluted with 125I-labeled hCG which was separated distinctly from hLH. The same fractions from this postmenopausal urinary gonadotropin preparation exhibited in vitro biological activity proportional to the immunocrossreactivity of the hCG-specific antiserum. Concentration of postmenopausal women''s urine by acetone precipitation retained approximately 5 times more immunoreactivity per unit volume than kaolin-acetone extraction when assayed with the antiserum to hCG.beta.-carboxyl-terminal peptide.