Glycoprotein clearance is rapid and suppressed by mannan in chicken embryos

Carbohydrates are thought to function as tags that mark circulatory glycoproteins for rapid clearance. Scavenger endothelial cells (SECs) play the primary role in clearing glycoproteins via receptor-mediated endocytosis in adult animals. We found that horseradish peroxidase (HRP), a glycoprotein, was removed quickly, mostly by receptor mediation from the chicken embryo circulation, but bovine serum albumin was not. The half-life of HRP in the circulation varied with the embryo stage and fell rapidly from 0.73 h at embryonic day 4 (E4) to 0.23 h at E5, with no great difference among stages after E5. HRP clearance was far slower at E3.5 than at E5, but was obviously suppressed by mannan. These results imply that the function of clearing glycoprotein or waste macromolecules from the circulation via receptor-mediated endocytosis appears early in the embryo.