A dramatic accumulation of glycogen in the brown adipose tissue of rats following recovery from cold exposure

In a morphological study of brown adipose tissue (BAT) of rats returned aft er exposure to cold (+5 degrees C) to neutral temperature (+25 degrees C), striking periodic acid Schiff staining was observed, indicating substantial glycogen accumulation. Enzymatic analysis revealed that the glycogen conte nt increased from the 4.05 +/- 0.51 (mu mol glucose unit per gram of tissue , mean +/- SE) control value to 57.3 +/- 9.66 when the animals were returne d to neutral temperature for 24 h after a 1-week cold period. Glycogen repl etion was also observed in liver and skeletal muscle; however, the glycogen levels in these tissues never exceeded the control values. The accumulatio n of glycogen in the BAT started by the 3rd hour of replacement and peaked by the 24th hour. This glycogen was readily utilized during the next short cold exposure of the animals. The plasma leptin concentration was reduced a t the cold temperature. The hexokinase II activity in the BAT increased to 29.3 +/- 1.46 vs the 11.8 +/- 1.06 control (mU/mg protein +/- SE) after a 1 -week cold exposure and this level was maintained during the return to neut ral temperature. The total glycogen synthetase (GStot) and the glycogen syn thetase a activity also increased after a 1-week cold exposure and increase d further during the replacement. The level of GStot reached 26.9 +/- 1.39 vs 9.54 +/- 1.43 control by the 24th hour of replacement, At the same time, the glycogen phosphorylase a activity declined during the replacement. The concentration of glucose g-phosphate (an activator of GS) decreased in the cold but returned to normal during the replacement, These changes in the B AT are in favor of glycogen synthesis, (C) 1999 Academic Press.