Comparison of 3-isobutyl-1-methylxanthine-induced accumulation of putrescine in rat pancreas and liver.

3-Isobutylmethylxanthine (IBMX), a potent phosphodiesterase inhibitor, causes accumulation of putrescine of same magnitude in rat pancreas and liver. IBMX produces increases of acetyl CoA: polyamine N'-acetyltransferase (PAT) and of ornithine decarboxylase (ODC) activities in both organs. However ODC activity is 300 times higher in liver than in pancreas. In the latter organ, there is a transient increase of N1-acetylspermidine, followed by a decrease of spermidine, alpha-Difluoromethylornithine (DFMO), a potent ODC inhibitor, impairs the accumulation of putrescine in liver but not in pancreas. These results suggest that in pancreas the accumulated putrescine is essentially formed from spermidine, via N1-acetylation and oxidation, while in liver it is formed from decarboxylation of ornithine. A possible involvement of cAMP in the stimulation of the polyamine interconversion pathway is discussed.