Selective induction of liver drug-metabolizing enzymes in rats exposed to a 21 ATA He-O2 environment.

The effects of prolonged exposure to a hyperbaric environment (21 ATA He-O2, 200 +/- 300 mm Hg O2, 32.5 +/- 1 degrees C) were investigated on the activity of rat liver drug-metabolizing enzyme systems, as monitored by O-dealkylation and N-dealkylation reactions. Continuous exposure of different groups of rats to a hyperbaric environment for 8, 22, 39, 57, or 84 d significantly increased the in vitro activity of drug-metabolizing enzymes in liver preparations obtained from rats subjected to prolonged exposures. The increase in the in vitro O-dealkylation of p-nitroanisole was selective; and the percent increases were 27, 146, 58, 40, 49, and 44 in liver preparations obtained from rats exposed continuously for 8, 22, 39, 57, 72, or 84 d, respectively. On the other hand, no statistically significant increase was observed in the in vitro activity of rat liver drug-metabolizing enzyme preparations during N-dealkylation of morphine and cocaine.