OXYGEN-TENSION, INSULIN, AND GLUCAGON AFFECT THE PRESERVATION AND INDUCTION OF CYTOCHROME-P450 ISOFORMS IN CULTURED RAT HEPATOCYTES

The role of oxygen tension, insulin, and glucagon on the preservation and induction of cytochrome P450 isoenzyme activities and contents was investigated in rat hepatocytes cultured for 4 days on crude liver me mbrane fractions at 4 or 13% O-2. At 13% O-2, three out of six immunoc hemically analyzed P450 isoenzymes were significantly higher than in 4 % O-2. Exposure to phenobarbital (PB) from Days 1 to 4 dose dependentl y increased the protein content and decreased the albumin secretion in 13% O-2 cultures only. The maximal induction of P450 isoenzymes CYP2B 1/2B2 (20- to 25-fold) and CYP2C6 (6-fold) were found at 0.75 mM PB at both oxygen tensions. In contrast, the highest induction of CYP1A1/1A 2 (3-fold), of CYP3A (2-fold), and EROD activity were found with 3 mM PB in 4% O-2 cultures. CYP2B-dependent testosterone hydroxylation at p ositions 16 alpha/beta was elevated to a greater extent in 13% O-2 cul tures (96-fold at 0.75 mM PB) compared to 4% O-2 cultures (42-fold). T his activity was affected by the insulin concentrations and the insuli n:glucagon ratio. With decreasing insulin concentration (100 to 1 nM) or with increasing insulin:glucagon ratios (1:100-1:0.1), the enzyme a ctivity increased preferentially in 4% O-2 cultures. The results of th ese investigations demonstrate that different tissue oxygen tension mo dulates the responsiveness of the cultured hepatocytes to the glucoreg ulatory hormones insulin and glucagon and this modulation results in a altered activity of cytochrome P450 isoforms. (C) I994 Academic Press , Inc.