Biochemical studies on regenerating liver.

Regenerating liver of the rat has long been recognized as a source of relatively abundant quantities of homogeneous rapidly growing tissue. Following the removal of the two largest lobes of the liver, the remaining ones, constituting about one-third of the total, enlarge to the size of the original liver in the span of a few days. The work of Higgins and Anderson (l), Brues et al. (2), and others has established that this enlargement is due to true hyperplastic growth. It therefore seemed to us an especially favorable tissue in which to test, by chemical analysis, the current view that nucleic acids are intimately related to growth. It should be noted that, although there is considerable indirect evidence to support this view, there is surprisingly little direct chemical data to demonstrate this relation. Caspersson and his colleagues (3-5) have shown an increased absorption of ultraviolet light, at 260 rnp, in the cytoplasm of actively growing cells. Stowell (6), using photometric histochemical methods, demonstrated a higher nucleic acid content in neoplastic tissue than in the homologous normal tissue. Brachet (7) has combined cytochemical techniques with the chemical estimation of furfural to reveal an increasing pentosenucleic acid (PNA) concentration during embryonic growth. Davidson and Waymouth (8) have estimated the PNA and desoxypentosenucleic acid (DNA) content of embryonic and adult tissues, and have found the concentration of both nucleic acids higher in embryonic than in adult tissues. Schneider and Klug (9) assayed rapidly growing tumors chemically and found them to have a high nucleic acid content. In this paper we shall present results which demonstrate a rise in PNA content of the liver when it is rapidly growing. We shall also present analyses, performed on the same tissue, for other substances which may be related to growth, lactic acid, glycogen, adenosine triphosphate, adenosine diphosphate, adenylic acid, and pentose phosphate, and for four oxidative enzyme systems, succinoxidase, malic dehydrogenase, cytochrome reductase, and oxalacetic oxidase.