Inhibition of hepatocyte proliferation in vivo by a glycopeptide from rat serum. 
The activity of a glycopeptide prepared from rat serum by treatment with trypsin and ultrafiltration was investigated in several in vivo proliferation systems.  In baby rat hepatocytes synchronized by a subcutaneous injection of casein solution it caused a G1-S block, stopping cells at the end of the G1 phase and sending them back to the G0 phase.  The glycopeptide also caused a G1-S block in young adult rats during the first semi-synchronized wave of proliferation that followed partial hepatectomy.  Inhibition of hepatocyte proliferation by the glycopeptide was suppressed by blood proteins from normal rats but not from acute phase rats.  Alpha 1-acid glycoprotein, an acute phase protein, increased this inhibition and reversed the antagonistic effect of normal blood proteins.  In normal baby rats a G1-S block of non-synchronously proliferating hepatocytes was produced in two situations in which the antagonistic effect of normal blood proteins was eliminated: after treatment of the glycopeptide with leucine-aminopeptidase, and after mixing it with alpha 1-acid glycoprotein.  The glycopeptide did not inhibit cell proliferation in kidney, submaxillary gland, or tongue epithelium.  It seems to be the active component of a system that inhibits the proliferation of hepatocytes, probably by reducing their sensitivity to various mitogenic stimuli.