In vivo quantification of removal of asialo-orosomucoid from the circulation in anaesthetized streptozotocin-diabetic rats.

The in vivo kinetic of removal of 3H asialo-orosomucoid from plasma was investigated in control and streptozotocin-diabetic rats after intravenous injection of 1 mg of asialo-orosomucoid/100 g body wt. Michaelis-Menten kinetics of disappearance were observed. In diabetic rats the maximal rate (Vmax) of disappearance of 3H asialo-orosomucoid was decreased by 30% with no modification of Michaelis constant. Since no accumulation of desialylated orosomucoid in the circulation was observed, the slower rate of removal of 3H asialo-orosomucoid was attributed to a decrease in the number of hepatic asialoglycoprotein receptors which are largely involved in the catabolism of asialoglycoproteins. Our estimate on in vivo maximal rates was 10- to 20-fold greater than our previous in vitro estimate of the maximal rate of endocytosis. In contrast, the values of the Michaelis constant obtained in vivo and in vitro were very similar.