Diurnal variations in circulating hormone levels and brown adipose tissue activity in "cafeteria"-fed rats.

Circulating hormone levels and interscapular brown adipose tissue (BAT) mitochondrial GDP-binding capacity were measured at 4-hr intervals over 24 hr in rats fed a stock diet or a palatable "cafeteria" diet. Plasma thyroxine, insulin and glucagon levels were unaffected by diet, but plasma triiodothyronine, BAT mass, mitochondrial protein content and GDP-binding were higher in cafeteria-fed rats. Blood glucose levels and BAT mitochondrial GDP-binding were higher at night in the cafeteria rats. The diurnal variations in these parameters correlated with changes in diet-induced thermogenesis previously observed in cafeteria-fed rats.