Chronic ethanol intake resulted in a significant decrease in the rate of rat ponderal growth and an impaired nyctohemeral profile of pineal N-acetyltransferase (NAT) activity. In ethanol-treated animals, the onset of the nocturnal NAT increase is delayed by 2 hours when compared to control animals. Moreover, pineal NAT nocturnal peak was reached at 4 h (2 hours later than controls), while pineal type II thyroxine 5′-deiodinase (5′-D) nyctohemeral profile was not modified by ethanol administration. The effect of ethanol administration (12 weeks) on 5′-D activity in different tissues was also studied. Ethanol induced a 5′-D activity increase in hypothesis and brain frontal cortex, when compared to control animals. No change in 5′-D activity is observed in either pineal gland, Harderian gland, or brown adipose tissue. Since basal values of 5′-D activity in hypophysis or brain frontal cortex are particularly dependent on serum thyroxine (T4) concentration, the effect of chronic ethanol administration on thyroid hormone levels was studied. Serum T4 levels in ethanol-treated animals were significantly decreased when compared to controls at any time point studied. However, no change in serum 3′,3,5-triiodothyronine (T3) levels were found.

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