Ethanol feeding and thyroid hormone monodeiodination.

Abstract

Adult male rats were placed on a 3 week regimen of ethanol (as 20% of total calories) in a nutritionally adequate diet, and controls were matched equicalorically without ethanol. Serum measurements of T4, T3, FT4, rT3, and TSH were performed in both the fed and the fasted state (18 hours). In the fed state, serum hormone measurements did not differ between control and ethanol-treated rats. Overnight fasting had a significant effect in decreasing serum T3 level in both experimental and control rats and in decreasing serum T4 level in ethanol-treated animals; FT4 and rT3 levels were not affected. Fasting also decreased in vitro hepatic T4 to T3 production to an equivalent degree in control and ethanol-treated rats, but did not alter hepatic T4 to rT3 production rates in control animals. In the fed state, hepatic rT3 neogenesis in animals given ethanol declined relative to the levels observed in control fed rats; fasting restored the depressed rT3 neogenesis to the levels noted in the fed state. Because decreased rT3 production in ethanol-treated rats in the fed state could not be explained on the basis of a change in 5'-deiodinase activity, it is suggested that ethanol administered with a nutritionally adequate diet may inhibit hepatic rT3 generation by inhibiting T4(5)-deiodinase.