One year of ethanol feeding increases circulating thyroid hormones in the dog

Nine greyhound dogs were fed ethanol for 1 year to examine the effects of long-term ethanol feeding on circulating thyroid hormones. The dose of ethanol consumed per day was 2 gm/kg for the first month, 3 gm/kg for the second month, and 4 gm/kg for the rest of the study. Plasma triiodothyronine (T3), thyroxine (T4), and reverse triiodothyronine (rT3) were measured by radioimmunoassay. Plasma T3 and T4 concentrations increased significantly during the period of ethanol administration compared with control values (ANOVA, P less than 0.005). Levels of rT3 showed a trend to increase, although this was not significant. Resin T3 uptake decreased significantly (ANOVA, P less than 0.005) and the calculated free T4 index and free T3 index showed significant elevations (ANOVA, P less than 0.005) during ethanol administration. The results of this study indicate that long-term ethanol feeding to dogs induces an increase in circulating thyroid hormones.