An indirect thyroxine stimulation of microsomal fatt acid desaturation in vitro.

Metabolically active intestinal epithelial cells were isolated using collagenase plus hyaluronidase. Oxygen consumption was measured and was found to be inhibited by KCN, antimycin A, and rotenone. Cells from 3-methylcholanthrene(MC)-treated rats metabolized benzo(α)pyrene (BP) at a rate that was 30-fold greater than control cells. The addition of salicylamide to the incubation medium inhibited conjugation of BP metabolites and facilitated the accumulation of fluorescent and ethylacetate extractable metabolites. Metyrapone, SKF 525-A, α-naphthoflavone (α-NF), and rotenone inhibited BP-metabolism in intestinal cells from MC-treated rats, with α-NF being the most inhibitory. In intestinal cells from control animals, metyrapone and SKF 525-A both inhibited BP metabolism, while α-NF and rotenone both produced an increase in the formation of fluorescent BP products. The distribution of metabolites from MC-treated rats was determined by high-pressure liquid chromatography and compared with authentic BP derivatives. Incubations were conducted for 5 and 30 min in the presence and absence of salicylamide, and 30-min samples incubated in the absence of salicylamide were hydrolyzed with β-glucuronidase or aryl sulfatase. In the absence of salicylamide, large amounts of conjugates were formed, the formation of which were inhibited by salicylamide addition. A product corresponding to the 4,5-oxide constituted the major metabolite after a 5-min incubation, while little dihydrodiol formation occurred. Large amounts of phenolic BP derivatives were also formed. After 30-min incubations, the percentage of products corresponding to the 4,5-oxide decreased, and an increase in dihydrodiol formation was observed. The slow metabolism of the 4,5-oxide and the slow accumulation of dihydrodiols is due to the presence of low epoxide hydrase activity in the intestine. Intestinal cells are capable of xenobiotic metabolism, and offer a convenient method of studying intestinal drug metabolizing processes which may significantly contribute to the overall xenobiotic metabolis in the body.