The effects of fractionated thermally oxidized corn oil on drug-metabolizing enzyme systems in the rat.

Corn oil samples were heated, with aeration, to 210 degrees C for a total of 5 hr. Both fresh and oxidized samples were urea-fractionated and the individual fractions were administered to male Sprague-Dawley rats by gastric intubation. The effects of urea adducts, adduct-free fractions, non-saponifiable fractions and unfractioned fresh and thermally oxidized oil samples on hepatic, intestinal and colonic drug-metabolizing enzymes were determined. The treatments had no significant effects on hepatic or intestinal drug-metabolizing or mixed-function oxidase activities. There was a significant (P less than 0.05) increase in colonic UDP-glucuronyltransferase activity in rats treated with thermally oxidized corn oil, while the non-saponifiable fraction of the same sample decreased (P less than 0.1) the activity of this enzyme. There was also a significant increase in the activity of colonic benzo[a]pyrene hydroxylase in rats treated with the non-adduct fraction or with urea adducts of the thermally oxidized corn oil. These data suggest the colon as a possible specific site for the alteration of mixed-function oxidase activities by products of thermally oxidized oils.