Mouse liver regeneration after carbon tetrachloride injury as test system for hepatic growth regulators

A test system for growth regulators based on the time course of liver regeneration in male NMRI mice injected intraperitoneally (ip) with 50 nmol CCl4 at 12 is described. Regenerative DNA synthesis (labelling index) peaked at 36 h after CCl4 injury, and the Colcemid-assessed mitotic rate (MR) at 42 h, i.e., 6 h later. This response pattern was used to assess the effects of factors in liver extracts that regulate or modulate hepatocyte proliferation. The effect of one, two, four or eight ip injections of an aqueous mouse liver extract on MR was tested at 48 h. A 30-70% inhibition was seen only after single injections at 12 h, 29 h or 44 h after CCl4 treatment. A 30-80% stimulation was observed after a single injection of the liver extract at 0, 5 or 24 h, and after two or four injections. The assay system could thus detect the presence of growth modulators in the extract. The experiments also showed that the timing was crucial. We recently isolated and characterized a growth inhibitory pentapeptide from mouse liver extracts. Using a synthetic pentapeptide with the same structure we reassessed the timing for growth inhibition seen with the liver extract. The following test system for growth inhibitors seemed most expedient: inhibitor administration at 29 h to affect G1-S transition, measured as reduced DNA synthesis at 36 h, or inhibitor administration at 44 h to affect G2-M transition, measured as reduced MR at 48 h.