Uptake of methylamine-activated alpha 2-macroglobulin by rat liver.

Serum clearance of alpha 2M-Me or alpha 2M-Tr is rapid and identical. Alpha 2M-Tr is almost exclusively taken up in the liver by the parenchymal cells; the uptake of alpha 2M-Me is equally shared between endothelial and parenchymal cells. Blocking the scavenger receptor on endothelial cells by polyinosinic acid reduces the uptake of alpha 2M-Me to 40% of the control value; under these conditions, alpha 2M-Me is only associated with the parenchymal cells. These results show the following: (1) activation of alpha 2M by methylamine or trypsin is different; (2) the scavenger receptor on endothelial cells functions as a system for the uptake of alpha 2M-Me in addition to the specific alpha 2M receptor on parenchymal cells.