Biological activity and tissue concentrations of TCDD and OCDD in rats after s.c. application alone and in combination

Abstract

We compared the liver enzyme induction in female rats after subcutaneous injection of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) and octachlorodibenzo- p-dioxin (OCDD) and correlated the effects with tissue concentrations of the substances. In the first experimental series rats were treated with 150 μg OCDD/kg body wt. Seven days after treatment OCDD concentrations in the liver ranged between 20 and 52 ng/g. No induction of EROD (ethoxy-resorufin-O-deethylase) activity was detectable. In the second series we treated rats daily for 6 consecutive days with 350 μg OCDD/kg body wt. One day after the last application the determination of EROD activity in the hepatic tissue revealed no enzyme induction as compared to vehicle-treated controls. OCDD liver concentrations ranged between 400 and 900 ng/g. Comparatively low concentrations (7 to 28 ng/g) were measured in adipose tissue. In two further experimental series one single dose of 100 ng 14C-TCDD/kg body wt was applied before or during the 6 day OCDD treatment. These results were compared with data from rats treated with TCDD only. TCDD treated rats showed a clear induction of monooxygenases, but no synergistic effect was detectable after the combined treatment. The TCDD liver concentration determined by scintillation counting was 0.75 ± 0.28 ng/g (mean ± S.D.; n = 24). OCDD caused no detectable changes of the TCDD concentration or of the biological effects induced by TCDD.