Ethanol Inhibition of Pituitary-Thyroid Axis: An Effect Secondary to Nutritional Deficiency

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Abstract
Ethanol as either 20 or 36% of total calories in a Lieber diet was administered to male rats. At these concentrations, ethanol consumption relative to body weight did not differ. Pair-fed controls were restricted to the amount of calories consumed by rats given ethanol. Under these conditions, a direct effect of ethanol on the hypothalamic-hypophyseal-thyroid axis could not be demonstrated. There were no differences between pair-fed control and ethanol treated rats in serum or pituitary TSH, TSH response to TRH, or T4 [thyroxine] and T3 [triiodothyronine] levels. In rats given ethanol as 36% of total calories and in their pair-fed controls (36% groups), a marked decrease in serum T4 levels occurred (25% and 30%) relative to the corresponding 20% groups. The decreased T4 in the 36% groups was associated with a pronounced fall in caloric intake, decreased serum TSH, and delcines in adenohypophyseal and body weight all of which were of similar magnitude in experimental and control rats. Thus, inanition probably was the primary cause of reduced thyroid function in the 36% groups. An interesting aspect of this change was the finding of no difference in serum T3 levels between pair-fed control and ethanol treated rats in the 36 and 20% groups despite the reduced T4 and caloric intake in 36% animals; the lack of decrease in T3 concentration in 36% animals may reflect augmented peripheral conversion of T4 to T3 or reduced T3 clearance.