IS DEGLYCOSYLATED HUMAN CHORIONIC-GONADOTROPIN AN ANTAGONIST TO HUMAN CHORIONIC-GONADOTROPIN - CHARACTERIZATION OF DEGLYCOSYLATED HUMAN CHORIONIC-GONADOTROPIN ACTION IN 2 TESTICULAR INTERSTITIAL CELL-FRACTIONS

In order to determine the significance of carbohydtrate residue of human chorionic gonadotropin )hCG) in receptor interaction and signal transduction leading to steriodogenesis, the effect of deglycosylated hCG (DG-hCH) was studied in vitro with two different hCG-responsive purified testicular interstitial cell fractions. Fractions I light cells, previously found to bind 125I-labeled hCG with high affinity witout producing testosterone, also bound 125I-labeled DG-hCG with high affinity (Kd 7.2·10-1) M) wihtout stimulating testosterone production. Fraction IV heavier cells, which produced testosterone in response to hCG without detectable high-affinity hCG-binding sites, neither bound DG-hCG nor sufficiently produced cAMP and testosterone in response. With the addition of intact hCG, DG-hCG inhibited cAMP levels, although not sufficiently to inhibit testosterone production. This observation was contrary to previous studied in which DG-hCG was shown to be antagonist to hCG action. We conclude that: (a) DG-hCG retains its binding activity in light cells and this high-affinity binding is unrelated to steroidogenesis; (b) DG-hCG does not bind to heavier cells with high affinity and loses its biological activity as results of deglycosylation; (c) DG-hCG actions in this study strengthen the concept of two different hCG-responsive cells in the rat interstitium which, if not separated, will yield misleading data supporting the coexistence of hCG high-affinity binding and biological responses in the same cell; and (d) DG-hCG partially anatagonizes the activation of adenylate cyclase but does not block testosterone production, thus questioning the usefulness of this analogue in antagonizing the action of native hCG in rat testis. © 1990.