Characterization of xenobiotic biotransformation in hepatic, renal and gut tissues of cattle and sheep.

Microsomal and cytosolic preparations of hepatic, renal, ileal and ruminal tissues of cattle and sheep were used to measure oxidative, hydrolative and conjugative biotransformations of 11 xenobiotic substrates. Within species, enzyme activities were generally higher (P less than .05) in hepatic than non-hepatic tissue but, in both species, non-hepatic tissue exhibited considerable capacities for metabolizing certain substrates. Sheep rumen wall (with papillae) was notably high in cytochrome P-450 content (34% of hepatic value), in glutathione conjugation of ethacrynic acid (223% of hepatic activity; P less than .05), and UDP-glucuronidation of estrone (290% of hepatic activity; P less than .05). Sheep differed (P less than .05) from cattle, having lower cytochrome P-450 content in liver and ileum (but not kidney); lower N-demethylase activity in liver, but two- to threefold higher activity in kidney; lower sulfotransferase activity in liver and kidney; and higher glutathione S-transferase activity toward certain substrates. UDP-glucuronidation varied too widely among substrates to afford strong generalization in comparisons among tissues or between species. Non-hepatic tissues in ruminants exhibit considerable capacities for oxidative, hydrolative and conjugative metabolism of xenobiotics. Sheep and cattle differ widely in hepatic and non-hepatic capacities for biotransforming certain xenobiotics.