EFFECT OF DESIALYLATED HUMAN CHORIONIC-GONADOTROPIN (HCG) ON THE BIOACTIVITY OF RAT LEYDIG-CELLS

Human chorionic gonadotropin is a glycoprotein hormone that, like LH, stimulates steroidogenesis in gonadal cells. Using a desialylation pro cess, 95 per cent of the sialic acid residues from an intact standard hCG molecule were eliminated and then the electrophoretic properties a nd the bioactivity of the desialylated hCG were determined. Using rat Leydig cells as a biological model, the binding affinity to LH recepto rs of Leydig cell membranes, steroidogenic activity and second messeng er production were studied. The results indicate that the loss of sial ic acid from the hCG molecule slightly increases the binding activity to LH receptors and results in steroidogenic activity with an increase d ED50. Cyclic AMP production was significantly reduced however and ar achidonic acid release was not observed. Several possible mechanisms t hat could explain these results are discussed. (C) 1998 John Wiley Bi Sons, Ltd.