ALTERATIONS OF INSULIN CONTENT AND INSULIN BINDING TO PLASMA-MEMBRANES IN RAT BROWN ADIPOSE-TISSUE DURING COLD-EXPOSURE AND COLD-ACCLIMATION

We ex-mined the insulin content, insulin binding to plasma membranes, and in vitro oxygen consumption of brown adipose tissue (BAT) from warm-acclimated (25-degrees-C), acute cold-exposed (5-degrees-C, 24 h: CE), and cold-acclimated (5-degrees-C, 4 weeks: CA) rats. Plasma insulin level was significantly lower in CE rats, but it did not differ between CA rats and warm controls. Insulin content per mg BAT weight from CE and CA rats were about three-times higher than those from controls. I-125-insulin binding to plasma membranes of BAT from CE rats was higher and that from CA rats was lower than that from respective warm controls. Scatchard plots analysis showed that the number of insulin binding sites per mg protein of BAT plasma membranes from CE rats increased by 100%, while that from CA rats decreased by 35% without any changes of affinity constant. Basal oxygen consumption of BAT from CE rats was higher than warm controls, and suppressed by insulin. Insulin did not affect basal oxygen consumption of BAT from CA and warm control rats. Noradrenaline-induced oxygen consumption of BAT from warm controls and CE rats was suppressed by insulin. These findings suggested that insulin was involved in the regulation of BAT thermogenesis by changing insulin status in BAT (content and binding to plasma membranes) during cold exposure and cold acclimation.