Ethanol feeding and thyroid hormone monodeiodination

Area of Science:

• Endocrinology
• Nutritional Science
• Toxicology

Background:

• Ethanol consumption can affect thyroid hormone levels.
• The impact of ethanol on thyroid hormone metabolism in nutritionally adequate diets requires further investigation.

Purpose of the Study:

• To investigate the effects of chronic ethanol administration on thyroid hormone profiles and hepatic deiodinase activity in rats fed a nutritionally adequate diet.
• To determine the influence of fasting on these parameters.

Main Methods:

• Adult male rats were administered ethanol (20% of calories) or an isocaloric control diet for 3 weeks.
• Serum thyroid hormones (T4, T3, FT4, rT3, TSH) were measured in fed and fasted states.
• In vitro hepatic T4 to T3 and T4 to rT3 production rates were assessed.

Main Results:

• Ethanol did not alter serum thyroid hormones in the fed state.
• Fasting decreased serum T3 and T4 in ethanol-treated rats.
• Ethanol reduced hepatic rT3 neogenesis in fed rats, an effect reversed by fasting.
• Hepatic T4 to T3 production was similarly decreased by fasting in both groups.

Conclusions:

• Chronic ethanol intake with an adequate diet inhibits hepatic reverse triiodothyronine (rT3) generation in the fed state.
• This inhibition may occur via the T4(5)-deiodinase pathway, independent of 5'-deiodinase activity.
• Fasting influences thyroid hormone levels and hepatic production, with ethanol-induced changes in rT3 production being state-dependent.