Regeneration of the liver in parabiotic rats.

Summary and Conclusions Partial hepatectomies have been performed on one partner of each of fourteen parabiotic pairs, and on two partners of each of three sets of parabiotic triplets. At intervals of 48 or 72 hours later, the intact livers of the nonhepatectomized partners all exhibited a higher mitosis rate than the control livers removed at the time of hepatectomy. In parabiotic twins the mean value was 6 times, and in triplets it was 50 times, that of the controls. Two of the fourteen pairs were sacrificed at 24 hours, and, in these, no significant alteration occurred in the livers of the nonhepatectomized partners. Biochemical determinations of alkaline phosphatase, total nitrogen, DNA, and water content failed to demonstrate significant differences. PNA values were increased slightly above the control levels in the nonhepatectomized partners of the twins but not in the triplets. All these entities are far less sensitive indices of proliferative activity than the mitotic count. The evidence suggests that in regenerating rat liver, mitosis is initiated by alterations in the chemical composition of the blood.