Metabolic effects of chronic T3 administration in the hypothalamic paraventricular and ventromedial nucleus in male rats

Thyroid hormone is a key regulator of energy metabolism. Apart from its direct effects on peripheral metabolism, thyroid hormone exerts acute metabolic effects via distinct nuclei within the hypothalamus. Recently, we developed a method for chronic and local intra-hypothalamic triiodothyronine (T3) administration in rats. The present study evaluated the metabolic effects of T3 delivered during either 7 or 28 days to the paraventricular or ventromedial nucleus (PVN or VMH). T3 administration for 7 days in the PVN decreased only plasma T3. There were no effects on body weight, food intake, plasma glucose concentrations, energy expenditure, locomotor activity and respiratory exchange rate (RER). In the liver and BAT, there were no changes in mRNA expression of genes involved in glucose metabolism and thermogenesis. T3 administration for 7 days in the VMH did not change any of these parameters. T3 administration for 28 days in the PVN decreased food intake without affecting body weight, glucose concentrations and body temperature. Liver and BAT gene expression was unaltered, except for decreased liver Dio1 mRNA. T3 administration for 28 days in the VMH did not affect liver and BAT mRNA expression, body weight, food intake and body temperature while blood glucose concentrations were slightly lower. In conclusion, we showed that chronic T3 administration to the PVN or VMH does not affect energy metabolism in a major way. Our results imply that the effects of intra-hypothalamic T3 administration on metabolism largely depend on the duration of treatment.