The role of insulin in norepinephrine turnover and thermogenesis in brown adipose tissue after acute cold-exposure.

The role of insulin in norepinephrine turnover (NE) and thermogenesis in brown adipose tissue (BAT) after acute cold-exposure was studied using streptozocin (STZ)-induced diabetic rats. NE turnover was estimated by the NE synthesis inhibition technique with alpha-methyl-p-tyrosine. BAT thermogenesis was estimated by measuring mitochondrial guanosine-5'-diphosphate (GDP), cytochrome oxidase activity and mitochondrial oxygen consumption in BAT at an ambient temperature of 22 degrees C and during a six-hour cold-exposure at 4 degrees C. In insulin-deficient diabetic rats, the NE turnover, mitochondrial GDP binding, cytochrome oxidase activity and mitochondrial oxygen consumption in BAT at 22 degrees C were significantly reduced, compared with those of control rats. Treatment of STZ-induced diabetic rats with insulin prevented a decrease in NE turnover and BAT thermogenesis. Acute cold-exposure increased the NE turnover of BAT in insulin-deficient diabetic rats. The BAT thermogenic response to acute cold-exposure, however, did not occur in insulin-deficient diabetic rats. These results suggest that insulin is not essential in potentiating NE turnover in BAT after acute cold-exposure, but is required for cold-induced thermogenesis.