Binding of alpha 2-macroglobulin to hepatocytes: mechanism of in vivo clearance.

The binding of 125I-labeled human alpha 2-macroglobulin-methylamine to adult rat hepatocytes in primary culture was studied at 4 degrees C. Cells which had been in culture for 4 hours exhibited steady state ligand binding after 1 hour, a receptor number of 22,400 receptors per cell, and a dissociation constant of 0.6 nM. Adult rat hepatocytes exhibited a significant decrease in receptor number with increased time in primary culture with less than 10% of the initial number of receptors remaining after 2 days (p less than 0.01). In autopsy studies of mice injected intravenously with 125I-labeled alpha 2-macroglobulin-methylamine, greater than 90% of the cleared ligand was found in the liver. Autoradiography of the liver demonstrated that 80% of the ligand was cleared by hepatocytes. It is concluded that the hepatocytes are the primary pathway for clearance from the circulation of receptor recognized alpha 2-macroglobulin.