Endurance exercise training does not alter lipolytic or adipose tissue blood flow sensitivity to epinephrine

We evaluated the relationship between lipolysis and adipose tissue blood flow (ATBF) in response to epinephrine and the effect of endurance exercise training on these responses. Five healthy untrained men underwent a four- stage incremental epinephrine infusion (0.00125, 0.005, 0.0125, and 0.025 μg · kg fat free mass^-1 · min^-1) plus hormonal clamp before and after 16 wk of cycle ergometry exercise training. Whole body glycerol and free fatty acid (FFA) rates of appearance (R(a)) in plasma were determined by stable isotope methodology, and ATBF was assessed by ¹³³Xe clearance. After each training session, subjects were fed the approximate number of calories expended during exercise to prevent changes in body weight. Glycerol R(a), FFA R(a), and ATBF increased when plasma epinephrine concentration reached 0.8 nM, but at plasma epinephrine concentrations >1.6 nM ATBF plateaued, whereas lipolysis continued to increase. Exercise training increased peak oxygen uptake by 24 ± 7% (2.9 ± 0.2 vs. 3.6 ± 0.1 l/min; P < 0.05) but did not alter body weight [70.5 ± 3.8 vs. 72.0 ± 3.8 kg; P = nonsignificant (NS)] or percent body fat (18.4 ± 1.6 vs. 17.8 ± 1.9%; P = NS). Lipolytic and ATBF responses to epinephrine were also the same before and after training. We conclude that the lipolytic and ATBF responses to epinephrine are coordinated when plasma epinephrine concentration is ≤1.6 nM, but that at higher epinephrine concentrations, lipolysis continues to increase while ATBF remains constant. Endurance exercise training does not change lipolytic or ATBF sensitivity to epinephrine infusion in vivo during resting conditions.