Localizations and biological activities of HCG fractions in rat organs.

This study was undertaken to determine which biological site or immunological site in the HCG molecule is essential for uptake of HCG by the ovaries. HCG was obtained from the urine of patients with trophoblastic dieseases by adsorption on kaolin. This preparation gave two distinct immunological fractions on Sephadex G-100 column chromatography. One fraction (antigen-1; Ag-1) had both gonadotropic and immunological activities present in HCG, while the other (antigen 2; Ag-2) had only immunological activity of HCG. 131I Ag-1 and 125I Ag-2 were injected into rats intravenously and the localizations of 131I and 125I in each organ and their subcellular fractions were measured by the paired label technique. After injection of HCG, Ag-1 and Ag-2, the activities of