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 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 Δ5-3β-hydroxysteroid dehydrogenase (3β-HSD) in the adrenals and ovaries were measured as an index of steroid biosynthesis. The results obtained were as follows: 1. 131I Ag-1 was taken specifically in the ovaries and the ratio of the 131I Ag-1 to 125I Ag-2 in the microsomal fraction was 14:1, 3hours after injection of the mixture containing cold HCG. The heated 131I Ag-1, which possessed only the immunological activity of HCG was not taken specifically in ovaries. These results suggest that the biological site in HCG molecule might be essential for picking up HCG by ovaries. 2. The percentage of 125I Ag-2 localization in kidney gradually increased, but no significant change was found in adrenals, thyroid, uterus, liver and blood. 3. 3β-HSD activity in the ovary was stimulated by the administration of HCG and Ag-1, but slightly inhibited by Ag-2. 3β-HSD activity in the adrenals was clearly inhibited by Ag-2. These results suggest that Ag-2 possibly has some other biological activity.