Effect of repeated carbon monoxide exposure to rats on cytochrome P-450 concentration and activities of monooxygenases in the liver.

To determine the possible role of cytochrome P-450 in the adaptation response of an organism to chronic carbon monoxide exposure, rats received 4, 15 or 30 subcutaneous CO injections (7.2 mmol/kg body mass; maximal COHb concentration about 56%). The concentration of cytochrome P-450 is significantly reduced after 4 injections. This effect is no longer evident following 15 or 30 CO injections, which produced distinct increases of the total hemoglobin concentration. Ethylmorphine N-demethylation is distinctly inhibited after 4, 15 and 30 CO injections, whereas the initial inhibition of ethoxycoumarin O-deethylation disappears after 30 CO administrations. Ethoxyresorufin O-deethylation is only slightly influenced by CO.