Characterization of Human Chorionic Gonadotropin Internalized by Pseudopregnant Rat Ovary*

Abstract

Peptide hormones may be internalized by target cells in a time- and dose-dependent manner. Since the predominant intracellular form of hCG internalized by cells of the pseudopregnant rat ovary was free, not receptor-bound, hormone, studies were undertaken to characterize subcellular hCG by Sephadex G-100 chromatography, Leydig cell bioassay, and binding to Concanavalin A-Sepharose 4B (Con A-Sepharose) 1, 3, 6, 12, and 24 h after the injection of groups of rats with a single 1.0-/xg dose of hCG (CR119). On Sephadex G-100 chromatography, a major immunoreactive hCG peak eluted slightly before the elution point of highly purified hCG. Smaller immunoreactive hCG peaks, consistent with degraded hCG, were observed and were prominent 6, 12, and 24 h after hormone injection. No free hCG subunits were observed. One hour after the iv hCG injection, the biological to immunological ratio of subcellular hCG was greatest; this progressively decreased at 3 and 6 h. However, no significant biological activity was present ...