Course of hepatic regeneration after 80% to 90% resection of normal rat liver. Comparison with two-lobe and one-lobe hepatectomy.

After subtotal (80% to 90%) hepatectomy of the normal rat liver, thymidine kinase activity began to increase after 24 hours and reached a maximum at 36 hours. This persisted for another 60 hours before it declined to reach the baseline by 7 to 8 days. The maximal increase was 30- to 50-fold. After two-lobe (67% to 78%) hepatectomy, the maximal increase was similar, but the onset and the maximum each occurred 12 hours earlier, and the maximum only persisted for another 24 hours. The important first peak of ornithine decarboxylase activity occurred earlier and rose higher after 67% to 78% hepatectomy. The distributions with time of histologic mitosis counts were similar to the distributions of thymidine kinase activity (reflects DNA synthesis) at each of the three levels of hepatectomy, 80% to 90%, 67% to 78% and 37% +/- 0.5%. Thus the initiation of regeneration was delayed after subtotal resection, but the regenerative response as reflected by DNA synthesis and cell multiplication was prolonged.