Effects of vitamin A and/or thyroidectomy on liver microsomal enzymes and their induction in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated rats

摘要: Abstract Vitamin A and thyroid hormone status have been shown previously to alter the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rats. In present study, we examined effects a vitamin A-excess A-deficient diet on levels, selected drug-metabolizing enzymes liver microsomes, their inducibility by TCDD male Sprague-Dawley Except for slight increase serum T3 none these end points was affected feeding rats diet. contrast, excess dietary caused decrease thyroxine (T4) triiodothyronine (T3) although levels remained euthyroid range (60–80 ng/dl). The concentration microsomal cytochromes P-450 b5 basal activity benzo[a]pyrene hydroxylase 7-ethoxyresorufin O-de-ethylase were unaffected A. This result is consistent with our previous observation that dependent more than T4 levels. markedly suppressed UDP-glucuronosyl transferase toward 1-naphthol. However, no such enzyme suppression observed thyroidectomized suggests suppressive effect may be T3. Neither nor had any major UDP- glucuronosyl cytochrome P-450-dependent activities TCDD. nearly additive T4. It concluded induction not associated modulatory hormones