Change of the hepatic cells in parabiosis between old and young rats.

The hepatic cells of the parabiotic unions 3 to 9 months after uniting between old and young rats were micrometrically examined. In the older parabiotic partners, it cannot be denied that the character of the findings tended in part towards that of the young controls. In the younger parabiotic partners, the estimated number of hepatic cells was apparently decreased, size of the hepatic cells and their nuclei was significantly increased, and number of binucleate hepatic cells was markedly increased. The findings of the hepatic cells in the younger partners were similar to those in the old controls. From the results, it is inferred that the proliferation of the hepatic cells of the younger parabiotic partners is inhibited by the inhibitory factors for cell division secreted from the hepatic cells of the older partners.