Studies on the metabolism of human tumors. III. Influence of regenerating liver on purine metabolism.

utilization patterns of hamsters and rats bearing human neoplasms. These studies showed that, in sofar as the synthesis of the purine moiety of their nucleic acids is concerned, these tumors possess distinctive characteristics as compared with the host tissues. In the synthesis of the nucleic acids, the neoplastic tissue used guanine and hypoxan thine inefficiently as compared with the host, but used adenine more extensively and glycine to an even greater degree. Other workers (5, 13) have reported findings consistent with the observation that tumors preferentially synthesize their nucleic acid purines de novo, even when the option of using preformed purines is available. In agreement with this concept, it has been shown that guanylic and adenylic acids are very poorly utilized as pre cursors of the nucleic acids of tumors relative to those of the host's tissues.' Knowledge about nucleic acid synthesis in an other rapidly growing tissue should permit a some what more lucid interpretation of the unusual pat tern of purine incorporation manifested by tumors. Cell division in the intestinal mucosa occurs at a rate comparable to that of the tumor (18), but cells are constantly being sloughed. A tissue grow ing at a rate greater than normal should be a more suitable basis for comparison. Such a system is regenerating liver. The cells formed by the hyper plastic liver are retained, thus obviating the objec tion to the use of intestinal mucosa as a reference rapidly growing tissue. Since the presence of rapidly multiplying cells does influence the metabolism of other tissues of an animal (e.g., the nucleic acid metabolism is al