Adrenaline and glycogenolysis in skeletal muscle during exercise: a study in adrenalectomised humans

The role of adrenaline in regulating muscle glycogenolysis and hormone-sensitive lipase (HSL) activity during exercise was examined in six adrenaline-deficient bilaterally adrenalectomised, adrenocortico-hormonal-substituted humans (Adr) and in six healthy control individuals (Con). Subjects cycled for 45 min at approximately 70% maximal pulmonary O2 uptake (VO2,max) followed by 15 min at approximately 86% VO2,max either without (-Adr and Con) or with (+Adr) adrenaline infusion that elevated plasma adrenaline levels (45 min, 4.49+/-0.69 nmol l(-1); 60 min, 12.41+/-1.80 nmol l(-1)). Muscle samples were obtained at 0, 45 and 60 min of exercise. In -Adr and Con, muscle glycogen was similar at rest (-Adr, 409+/-19 mmol (kg dry wt)(-1); Con, 453+/-24 mmol (kg dry wt)(-1)) and following exercise (-Adr, 237+/-52 mmol (kg dry wt)(-1); Con, 227+/-50 mmol (kg dry wt)(-1)). Muscle lactate, glucose-6-phosphate and glucose were similar in -Adr and Con, whereas glycogen phosphorylase (a/a + b x 100 %) and HSL (% phosphorylated) activities increased during exercise in Con only. Adrenaline infusion increased activities of phosphorylase and HSL as well as blood lactate concentrations compared with those in -Adr, but did not enhance glycogen breakdown (+Adr, glycogen following exercise: 274+/-55 mmol (kg dry wt)(-1)) in contracting muscle. The present findings demonstrate that during exercise muscle glycogenolysis can occur in the absence of adrenaline, and that adrenaline does not enhance muscle glycogenolysis in exercising adrenalectomised subjects. Although adrenaline increases the glycogen phosphorylase activity it is not essential for glycogen breakdown in contracting muscle. Finally, a novel finding is that the activity of HSL in human muscle is increased in exercising man and this is due, at least partly, to stimulation by adrenaline.