Tissue distribution, excretion and biological effects of [14C]tetrachlorodibenzo-p-dioxin in rats.

Abstract When Sprague-Dawley rats weighing 200 g were intubated intragastrically with 14 C-labelled 2,3,7,8-tetrachlorodibenzo- p -dioxin in a dose of 50 μg/kg body weight, 50% of the animals died within 25 days. Over 56% of the radioactivity was eliminated, mainly by the alimentary route, during the initial 21 days, 25% being accounted for during the first 3 days. The total amount of radioactivity in the urine was 4·5% of the total dose, the highest daily levels being excreted toward the end of the experiment. A large percentage of the radioactivity remaining in the body was localized in the liver and of this, over 90% was within the microsomal fraction. The major morphological changes in these rats were a marked liver hypertrophy and thymic regression.