Effect of diet and cold exposure on norepinephrine turnover in pancreas and liver

The potential contribution of the sympathetic nervous system to the regulation of the endocrine pancreas and the liver has previously been studied only in vitro or by indirect in vivo methods. This report describes the adaptation of the [³H]norepinephrine ([³H]NE) turnover technique to rat pancreas and liver as well as the application of this technique to the evaluation of sympathetic activity in these organs during cold exposure, fasting, and overfeeding. Cold exposure (4°C) increased the calculated pancreatic NE turnover rate 83% from 16.6 ± 1.1 ng NE/organ per hr to 30.4 ± 1.9 (95% confidence intervals), whereas hepatic NE turnover rate increased only 25% from 47.0 ± 3.4 to 58.7 ± 3.3. Two days of fasting reduced pancreatic NE turnover rate 70% from 26.8 ± 3.0 ng NE/organ per hr to 8.0 ± 0.8, whereas hepatic NE turnover rate decreased 48% from 41.6 ± 3.2 to 21.8 ± 2.4. Three days of overfeeding with sucrose increased pancreatic NE turnover rate 68% from 9.7 ± 1.6 ng NE/organ per hr to 16.3 ± 2.2, whereas hepatic NE turnover rate increased 96% from 32.7 ± 5.7 to 64.0 ± 9.3. Studies with the ganglionic blocking agent chlorisondamine generally support the thesis that changes in NE turnover in pancreas and liver reflect changes in sympathetic activity, the only discrepancy occurring in the liver during sucrose feeding. Thus, increased sympathetic activity may explain some of the endocrine-metabolic adjustments to cold exposure. Changes in sympathetic activity may explain some of the endocrine-metabolic adjustments to cold exposure. Changes in sympathetic activity during fasting, however, cannot readily explain the increased substrate mobilization that accompanies the fasting state.