Alteration by phenobarbital of membrane-associated enzymes including gamma glutamyl transpeptidase in mouse liver neoplasms.

Administration of phenobarbital for 5 to 7.5 weeks to aged C3HfB/HeN mice with spontaneous liver tumors produced an enhancement of gamma glutamyl transpeptidase activity in the tumors and a decrease in glucose-6-phosphatase and adenosine triphosphatase activity. Discontinuation of phenobarbital feeding for 5.5 weeks resulted in the loss of gamma glutamyl transpeptidase activity in tumors. These findings of alterations in three membrane-associated enzymes indicate that phenobarbital produces substantial changes in the composition of cellular membranes which may be related to its promoting activity.