EFFECT OF PERIPORTAL-EQUIVALENT AND CENTRILOBULAR-EQUIVALENT OXYGEN-TENSION ON LIVER-SPECIFIC FUNCTIONS IN LONG-TERM RAT HEPATOCYTE CULTURES

The influence of periportal- and centrilobular-equivalent oxygen tensi ons on cellular functions and xenobiotic metabolism was investigated i n rat hepatocytes cultured under 20% (air/CO2), 13% or 4% O-2 for up t o 9 days on teflon membrane dishes, coated with crude membrane fractio ns and collagen. Protein content, total cytochrome P-450 content, 7-et hoxy-resorufin-O-deethylase (EROD) and the profile of hydroxytestoster one metabolites were not significantly affected by the oxygen tension, whereas intracellular lactate dehydrogenase activity and albumin secr etion were increased at 4% O-2 in comparison with 13 and 20% O-2 cultu res. The induction of P-450 isoenzymes and corresponding catalytic act ivity was determined on days 4 and 9, following a 3-day exposure to ph enobarbital (PB, 0.75 mM) or 3-methylcholanthrene (3-MC, 6.25 mu M). O n day 4, PB increased CYP2B1/B2 content 19-fold (4% O-2) or 27-fold (1 3% O-2), CYP2C6 six-fold at both oxygen tensions, and CYP3A2 two-three -fold only in 4% O-2 cultures. On day 9, CYP2B1/B2 was still significa ntly increased. A clear correlation was found between P-450 isoenzyme content and corresponding isoenzyme activities, as assayed by testoste rone hydroxylation and EROD activity on day 4. 3-MC increased CYP1A1/2 11-fold and eight-fold in 4 and 13% O-2 cultures, respectively, and t he EROD activity 37-fold (4% O-2) and 30-fold (13% O-2) on day 4. Acti vities were still measurable on day 9, whereas the corresponding apopr oteins CYP1A1 was not detectable. These results suggest that hepatocyt es are able to adapt their xenobiotic metabolism to different tissue o xygen tensions and confirm the likelihood that oxygen tension is an im portant modulator of the region-specific expression of xenobiotic meta bolism in liver.