1,2-Dimethylhydrazine-induced alterations in N1-acetylspermidine levels and spermidine N1-acetyltransferase activity in rat colonic mucosa.

To determine whether alterations in the "reverse" or "conversion" pathway for putrescine formation were involved in the induction of colonic tumors by 1,2-dimethylhydrazine, male albino rats of the Sherman strain were given injections s.c. of this agent (20 mg/kg body weight/week) or diluent for 5, 10, 15, and/or 26 weeks. Animals were sacrificed at each of these time periods and polyamine levels, including N1- and N8-acetylspermidine, as well as the activities of ornithine decarboxylase, spermidine N1-acetyltransferase and polyamine oxidase were measured and compared in rat proximal and distal colonic mucosa of each group. The results of these studies demonstrated that: (a) N1- and N8-acetylspermidine levels were similar in the control and treated proximal colonic segments at all time periods examined; (b) N1- and N8-acetylspermidine levels were also similar in the control and treated distal colonic segments at 5 and 10 weeks; (c) at 15 weeks the level of N1-acetylspermidine, but not N8-acetylspermidine, however, was increased in the treated distal colonic segment secondary to increases in the activity of spermidine N1-acetyltransferase; and (d) at 26 weeks, the level of N1-acetylspermidine remained higher in treated distal "uninvolved" colonic tissue and were markedly elevated in colonic tumors in both segments. Based on these findings, it would appear that the reverse pathway for putrescine formation may be involved in the 1,2-dimethylhydrazine-induced malignant transformation process of the rat colon.