Hormonal, metabolic, and cardiovascular responses to 21 min of cycling in three saline- or
glucose-infused men with
McArdle's disease were compared with those of matched controls to elucidate whether mobilization of extramuscular fuel is enhanced to compensate for the lack of intramuscular glycogenolysis in patients with
McArdle's disease. During exercise, all saline-infused patients compared with controls working at both the same absolute and at similar relative work rates had higher
glucose production (31 +/- 7 vs. 19 +/- 5 and 26 +/- 4 mumol.min-1.kg-1) and utilization (34 +/- 8 vs. 22 +/- 2 and 28 +/- 4 mumol.min-1.kg-1); higher plasma
glycerol (155 +/- 19 vs. 75 +/- 20 and 90 +/- 22 mumol/l),
free fatty acids (487 +/- 175 vs. 295 +/- 47 and 202 +/- 52 mumol/l),
growth hormone (7.7 +/- 2.8 vs. 2.6 +/- 1.1 and 3.6 +/- 3.4 mU/l), and
cortisol (530 +/- 168 vs. 268 +/- 8 and 367 +/- 80 nmol/l), greater decrease in
insulin (delta 57 +/- 4 vs. delta 11 +/- 8 and delta 11 +/- 23 pmol/l), and similar
glucose concentrations. Furthermore,
norepinephrine,
epinephrine, and
adrenocorticotropic hormone levels were higher and heart rate and cardiac output were higher during exercise in all patients than in controls at the same absolute work rate.
Glucose infusion induced
hyperglycemia and
hyperinsulinemia in patients and inhibited the exercise-induced increases in
glucose production,
glycerol,
free fatty acids,
catecholamines,
growth hormone,
cortisol, and heart rate. In conclusion, feedback from metabolism in contracting muscle enhances hormonal responses and extramuscular substrate mobilization during exercise in
McArdle's disease.