Effects of thyroid hormone on food intake, hypothalamic Na/K ATPase activity and ATP content.

The effects of thyroid hormone on whole body energy metabolism and compensatory effects on food intake are well established. However, the hypothalamic mechanisms that translate perceived whole body energy demands into subsequent appetitive behavior are incompletely understood. In order to address this question, we tested the effects of T3 on food intake and body weight in rats and measured neuronal Na/K ATPase activity and ATP content in the hypothalamus. Intraperitoneal T3 (100 microg/kg BW) administered for 6 consecutive days increased 24-h rat food intake from control, 26.6+/-1.2, to T3-treated 33.2+/-1.6 g (P<0.01). In T3-treated rats, rubidium-86 (86Rb) uptake (measured as a marker of Na/K ATPase activity) in ex vivo hypothalamic tissue increased (P<0.01) while the content of ATP in the ventral hypothalamus declined following T3 treatment (P<0.01). In another model of energy deficit, which was induced by a very low calorie diet, ATP content was also reduced in the hypothalamus compared to rats fed ad libitum. In summary, increased food intake in response to T3 may be secondary to decreased hypothalamic ATP content, perhaps resulting from both increased Na/K ATPase activity in the hypothalamus and metabolic signaling induced by whole body caloric deficit.