Cold-induced and diet-induced thermogenesis in progesterone-treated rats

Both cold-acclimated rats and rats at thermoneutrality received 1.5 mg/day of progesterone over a period of 15 days by means of two subcutaneously implanted Silastic capsules. Progesterone treatment increased total food intake and body mass gain in both groups of treated animals when compared with their controls at the same ambient temperature. However, the interscapular brown adipose tissue (BAT) of the treated rats showed the same thermogenic activity (assessed by GDP-binding), mass and gross composition as that of their respective controls. If it is assumed that enhanced food intake is the physiological drive for diet-induced thermogenesis, it could be concluded that progesterone inhibits diet-induced thermogenesis at thermoneutrality, but has no effect in cold-induced thermogenesis. However, if the physiological drive for diet-induced thermogenesis is not enhanced food intake, but an imbalance in the diet, then given that the same diet was offered to all animals throughout the experimental period, it could be that progesterone does not affect BAT, either at thermoneutrality or in the cold.