LIPOLYTIC AND ADIPOSE TISSUE BLOOD FLOW SENSITIVITY TO EPINEPHRINE BEFORE AND AFTER ENDURANCE TRAINING

Abstract

1723 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 (26±3 yr) 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 weeks of cycle ergometry exercise training. Whole-body glycerol and free fatty acid (FFA) rates of appearance (Ra) 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 Ra, FFA Ra, and ATBF increased above basal values (P<0.05) when plasma epinephrine concentration reached 0.8 nM (58±16%, 62±15%, 235±44%, respectively) and increased progressively as plasma epinephrine concentration increased to 1.6 nM. However, at plasma epinephrine concentrations >1.6 nM, ATBF plateaued while lipolysis continued to increase. Exercise training increased peak oxygen uptake by 24±7% (P<0.05) but did not alter body weight (70.5±3.8 vs. 72.0±3.8 kg; P=NS), or %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 at higher epinephrine concentrations lipolysis continues to increases while ATBF remains constant. Endurance exercise training does not change lipolytic or ATBF sensitivity to epinephrine in vivo.