Norepinephrine spillover in forearm and subcutaneous Adipose tissue before and after eating

The sympathetic nervous system regulates lipolysis. There are regional differences in the sensitivity of lipolysis to adrenergic regulation. Little is known about regional sympathetic activity in response to eating in humans. We studied the effect of feeding on systemic and local sympathetic nervous system activity and lipolysis in lean healthy subjects (three women and five men; age, 27.0 ± 2.0; body mass index, 23.4 ± 1.2 kg/m^-2) using isotope dilution methodology and arterio-venous sampling. Feeding increased arterial norepinephrine (NE) concentration (mean premeal, 0.96 ± 0.12 nmol/L·L; mean postmeal, 1.28 ± 0.14 nmol/L·L; P < 0.02) and total body NE spillover (mean premeal, 2.11 ± 0.30 nmol/min·L; mean postmeal, 2.76 ± 0.31 nmol/min·L; P < 0.02), whereas the arterial epinephrine concentration decreased (mean premeal, 289 ± 61 pmol/L; mean postmeal, 170 ± 5 pmol/L; P < 0.02). Palmitate concentration and total body systemic rate of appearance of palmitate declined postprandially (mean premeal, 117 ± 15 μmol/min; mean postmeal, 38 ± 4 μmol/min; P < 0.01). NE spillover increased by the same proportion in both forearm and adipose tissue [in forearm, mean premeal and postmeal, 1.02 ± 0.11 and 2.41 ± 0.44 nmol/100 mL·min, respectively (P < 0.02); in adipose tissue, mean premeal and postmeal, 0.41 ± 0.12 and 0.73 ±0.17 nmol/100 g·min, respectively (P < 0.02)]. The results show that a meal caused differential changes in systemic sympatho-adrenal activity and an increase in sympathetic activity in adipose tissue postprandially, However, this increase in postprandial sympathetic activity was not enough to overcome the inhibition of lipolysis by insulin.