Comparison of enhancement of GGTase-positive foci and induction of ornithine decarboxylase in rat liver by barbiturates.

The indication of ornithine decarboxylase (ODC) by barbiturates and the ability of barbiturates to enhance neoplastic progression of chemically initiated cancer was examined in rat liver. All seven barbiturates induced ODC with barbital (7.7 fold increase) and phenobarbital (5.7 fold increase) demonstrating the most potent activity. Maximum induction of ODC by phenobarbital was obtained in 18 h. Barbital (500-5000 p.p.m.) and phenobarbital (500 p.p.m.) administered in the drinking water enhanced the appearance of diethylnitrosamine (DENA)-initiated gamma- glutamyltranspeptidase (GGTase)-positive foci. Amobarbital, hexabarbital and pentabarbital did not enhance the appearance of GGTase-positive foci. In the absence of previous initiation by DENA, the enhancing regimen of the barbiturates did not cause the appearance of GGTase-positive foci. Barbiturates induced ODC activity in rat liver and enhanced the incidence of DENA initiated GGTase-positive foci.