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.

中文翻译：

---

糖蛋白清除迅速并被鸡胚胎中的甘露聚糖抑制。

碳水化合物被认为作为标记循环糖蛋白以快速清除的标签。清道夫内皮细胞 (SEC) 在成年动物中通过受体介导的内吞作用清除糖蛋白中起主要作用。我们发现辣根过氧化物酶 (HRP) 是一种糖蛋白，主要通过鸡胚胎循环中的受体介导被快速去除，但牛血清白蛋白则不然。HRP 在循环中的半衰期随胚胎阶段而变化，从胚胎第 4 天（E4）的 0.73 小时迅速下降到 E5 的 0.23 小时，E5 之后各阶段之间没有太大差异。E3.5 的 HRP 清除比 E5 慢得多，但明显被甘露聚糖抑制。