Responses of the D-glucuronic acid pathway in rat tissues to treatment with tetrachlorodibenzodioxin.

1. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) was administered to rats to study its effects on the enzyme activities of the D-glucuronic acid pathway in the liver, small intestine and kidney. 2. The UDP-glucuronosyl transferase activity of male albino rats given TCDD (80 mug/kg, one dose, i.p.) 6 days before killing was significantly increased in all tissues examined, and UDP-glucuronic acid pyrophosphatase activity was markedly decreased in the liver. D-Glucuronolactone and L-gulonate dehydrogenase activities in the liver and small intestine were slightly decreased after TCDD treatment. 3. The activities of UDP-glucose dehydrogenase and beta-glucuronidase were unchanged. 4. The 24 h urinary excretion of L-ascorbic acid was enhanced 8-fold, although no difference was detected in the excretion of D-glucaric acid between the control and experimental animals. 5. These results suggest an increased capacity for glucuronide conjugation after treatment with TCDD. 6. The lack of increase in the urinary excretion of D-glucaric acid further challenges its use as a reliable indicator of enhanced drug metabolism.