Norepinephrine spillover from human adipose tissue before and after a 72-hour fast

Adipose tissue lipolysis is at least in part stimulated by the sympathetic nervous system (SNS). Although there is a generalized decrease in SNS activity with fasting, the rate of lipolysis during fasting increases. The aim of this study was to determine whether there is an association between activation of sympathetic nerves innervating adipose tissue and the increase in lipolysis seen during fasting in humans. We used the isotope dilution technique to measure regional norepinephrine spillover from abdominal sc adipose tissue from seven healthy subjects before and after a 72-h fast. Our results showed a significant increase in adipose tissue spillover of norepinephrine (mean ± SEM, 0.40 ± 0.09 vs. 1.08 ± 0.18 pmol·100 g^-1·min^-1, P < 0.05) and arterial norepinephrine concentrations (0.92 ± 0.10 vs. 1.23 ± 0.08 nmol·liter^-1, P < 0.05) after the fast with no significant change in total body norepinephrine spillover, forearm norepinephrine spillover, epinephrine concentrations, or energy expenditure. We show for the first time, in humans, a selective regional increase in adipose tissue norepinephrine spillover in response to a 72-h fast and suggest that the SNS may play a greater role in the regulation of lipid metabolism during fasting than previously thought.