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Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
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 (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 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.
lipolysis; triglycerides; catecholamines; stable isotopes; pancreatic clamp
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