Sulphonylureas and glucose metabolism in phenobarbital induced rats.

The addition of phenobarbital (PB) to a sulphonylurea (SU) regimen may improve glycemic control in patients with non- insulin dependent diabetes mellitus (NIDDM, type II). Since SU reactions may be modified, we investigated glucose metabolism in rats with combined PB and SU treatment. Chlorpropamide (CHL) and glibenclamide (GB) were selected as SU drugs. The combination of PB to the CHL or GB regimens induced the drug metabolism enzymes excluding aminopyrine N-demethylase activity, which was enhanced by GB but not CHL. The CHL and GB treatments lowered blood glucose (BG) concentration and decreased hepatic glucose-6-phosphate phosphohydrolase (G6P hydrolase) activity and glycogen reserves in the rats. The concomitant administration of PB and the SUs decreased hepatic G6P hydrolase activity and glycogen content in the animals, whereas the BG level remained unaltered. The hepatic glycogen content was decreased more markedly in the CHL plus PB than in the CHL alone treated animals. The findings suggests that enzyme inducers modify the action of SU in rats. Hepatic drug and glucose metabolizing enzymes seems also to respond to distinct PB plus SU combinations in different ways.