Tissue-specific effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the activity of 5'-deiodinases I and II in rats

Toxicol Lett. 2004 Mar 1;147(2):133-42. doi: 10.1016/j.toxlet.2003.10.025.


Thyroid hormones play a complex role in the toxicity of polychlorinated dibenzo-p-dioxins and furans and related compounds. We investigated the toxicological significance of 5'-deiodinases I and II (5'-DI and 5'-DII) in the altered thyroid hormone status of TCDD-treated rats. Time courses and dose responses were determined for serum thyroxine (T4) and triiodothyronine (T3) levels, for 5'-DI activity in thyroid gland, liver and kidney, and for 5'-DII activity in brown adipose tissue (BAT). TCDD-treatment resulted in prompt and dose-dependent decrease in circulating T4 followed by a decrease in liver 5'-DI activity 1-2 days later and an apparent increase in BAT 5'-DII activity. Changes in liver 5'-DI and BAT 5'-DII activity were secondary to decreased T4 levels. Thyroid and kidney 5'-DI activities as well as circulating T3 levels were not affected. The results suggest that altered 5'-DI or 5'-DII activities do not significantly influence the circulating levels of T4 or T3 in TCDD-treated rats.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adipose Tissue, Brown / drug effects
  • Adipose Tissue, Brown / enzymology
  • Animals
  • Body Weight / physiology
  • Cytochrome P-450 CYP1A1 / metabolism
  • Dose-Response Relationship, Drug
  • Iodide Peroxidase / metabolism*
  • Isoenzymes / metabolism
  • Kidney / drug effects
  • Kidney / enzymology
  • Liver / drug effects
  • Liver / enzymology
  • Male
  • Polychlorinated Dibenzodioxins / toxicity*
  • Rats
  • Rats, Sprague-Dawley
  • Thyroid Gland / drug effects
  • Thyroid Gland / enzymology
  • Thyroid Hormones / metabolism
  • Time Factors
  • Tissue Distribution


  • Isoenzymes
  • Polychlorinated Dibenzodioxins
  • Thyroid Hormones
  • Iodide Peroxidase
  • Cytochrome P-450 CYP1A1