Asialoglycoprotein receptor is uninvolved in clearing intact glycoproteins from rat blood

The hypothesis that the hepatic receptor for asialoglycoproteins would mediate turnover of glycoproteins in blood (after their desialylation by neuraminidase located on cell surfaces) was tested in rats by measuring clearance of intact 125I-labeled glycoproteins in the presence or absence of enough unlabeled asialoglycoproteins to saturate the asialoglycoprotein receptor. Via an indwelling venous catheter, a mixture of 125I-orosomucoid (obtained from rat serum) and a bolus of unlabeled asialofetuin (bovine) was injected, and infusion of an asialofetuin solution sustained. Total radioactivity and trichloroacetic acid-precipitable radioactivity were measured in blood samples taken at frequent intervals from an arterial catheter. Clearance was computer analyzed by using a two-component model. Nondestructiveness of radiolabeling and desialylation methods and interchangeability of rat and bovine (asialo)glycoproteins were demonstrated in control experiments. The infusion trials showed that independent clearance processes exist for intact and asialoglycoproteins. Apparently, the asialoglycoprotein receptor has no function in the turnover of intact plasma glycoproteins.