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Thyroid function and thyroxine metabolism in hexachlorobenzene-induced porphyria.
D L Kleiman de Pisarev1, M C Rios de Molina, L C San Martin de Viale
1Departmento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Núñez, Argentina.
Biochemical Pharmacology
|March 1, 1990
Summary
Hexachlorobenzene (HCB) exposure in rats increased liver weight and altered thyroid hormone metabolism, leading to porphyria. Serum thyroxine (T4) levels decreased, indicating HCB
Area of Science:
- Toxicology and Environmental Health
- Endocrinology and Metabolism
Background:
- Hexachlorobenzene (HCB) is an environmental pollutant with known toxic effects.
- Previous studies suggest HCB can interfere with endocrine functions, particularly thyroid hormones.
- The specific impact of HCB on porphyria development and thyroid hormone metabolism requires further elucidation.
Purpose of the Study:
- To investigate the effects of HCB administration on porphyria development in rats.
- To examine the impact of HCB on thyroid function and thyroid hormone metabolism.
- To determine the sensitivity of serum thyroxine (T4) and porphyrinogen carboxy-lyase (PCL) activity to HCB exposure.
Main Methods:
- Female Wistar rats were administered HCB for 1 or 8 weeks.
- Measurements included liver and thyroid weight, serum T4 and triiodothyronine (T3) levels, and [125I] incorporation.
- Assays for protein-bound iodine (PB[125I]), hepatic T4 metabolism, porphyrin excretion, aminolaevulinate synthase, and PCL activity were performed.
Main Results:
- HCB increased liver weight and altered thyroid hormone metabolism, increasing T4 dehalogenation.
- Serum T4 levels were significantly depressed, while T3 levels remained largely unchanged.
- HCB induced porphyria after 8 weeks, characterized by inhibited PCL activity and altered porphyrin metabolism.
Conclusions:
- HCB exposure enhances hepatic thyroxine metabolism without affecting thyroid hormone synthesis.
- Serum T4 levels and PCL activity show differential responses to HCB, with serum T4 being a more sensitive indicator.
- HCB is a potent inducer of porphyria and thyroid hormone disruption.