Role of the sympathoadrenergic system in adipose tissue metabolism during exercise in humans

1. The relative roles of sympathetic nerve activity and circulating catecho lamines for adipose tissue lipolysis during exercise are not known, 2. Seven paraplegic spinal cord injured (SCI, injury level T3-T5) and seven healthy control subjects were studied by microdialysis and (133)xenon wash out in clavicular (CI) and in umbilical (Um) (sympathetically decentralized in SCI) subcutaneous adipose tissue during 1 h of arm cycling exercise at similar to 60 % of the peak rate of oxygen uptake. 3. During exercise, adipose tissue blood flow (ATBF) and interstitial glyce rol, lactate and noradrenaline concentrations increased significantly in bo th groups. Plasma catecholamine levels increased significantly less with ex ercise in SCI than in healthy subjects. The exercise-induced increase in in terstitial glycerol concentration in subcutaneous adipose tissue was signif icantly lower in SCI compared with healthy subjects (SCI: 25 +/- 12 % (CI), 36 +/- 20 % (Um); healthy: 60 +/- 17 % (CI), 147 +/- 45 % (Um)) and the in crease in ATBF was significantly lower (CI) or similar (Um) in SCI compared with healthy subjects (SCI: 1.2 +/- 0.3 ml (100 g)(-1) min(-1) (CI), 1.0 /- 0.3 ml (100 g)(-1) min(-1) (Um); healthy: 2.8 +/- 0.7 ml (100 g)(-1) min (-1) (CI), 0.6 +/- 0.3 ml (100 g)(-1) min(-1) (Um)). Accordingly, in both a dipose tissues lipolysis increased less in SCI compared with healthy subjec ts, indicating that circulating catecholamines are important for the exerci se-induced increase in subcutaneous adipose tissue lipolysis. In SCI subjec ts, the exercise-induced increase in subcutaneous adipose tissue lipolysis was not lower in decentralized than in sympathetically innervated adipose t issue. During exercise the interstitial noradrenaline and adrenaline concen trations were lower in SCI compared with healthy subjects (P < 0.05) and al ways lower than arterial plasma catecholamine concentrations (P < 0.05). 4. It is concluded that circulating catecholamines are important for the ex ercise-induced increase in subcutaneous adipose tissue lipolysis while symp athetic nerve activity is not.