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

1. The role of adrenaline in regulating muscle glycogenolysis and hormone-s ensitive lipase (HSL) activity during exercise was examined in six adrenali ne-deficient bilaterally adrenalectomised, adrenocortico-hormonal-substitut ed humans (Adr) and in six healthy control individuals (Con). 2. Subjects cycled for 45 min at similar to 70% maximal pulmonary O-2 uptak e (V-O2,max) followed by 15 min at similar to 86 % V-O2,max either without (-Adr and Con) or with (+Adr) adrenaline infusion that elevated plasma adre naline levels (45 min, 4.49 +/- 0.69 nmol 1(-1); 60 min, 12.41 +/- 1.80 nmo l 1(-1)). Muscle samples were obtained at 0, 45 and 60 min of exercise. 3. In -Adr and Con, muscle glycogen was similar at rest (-Adr, 409 +/- 19 m mol (kg dry wt)(-1) Con, 453 +/- 24 mmol (kg dry wt)(-1)) and following exe rcise (-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 (% pho sphorylated) activities increased during exercise in Con only. Adrenaline i nfusion increased activities of phosphorylase and HSL as well as blood lact ate concentrations compared with those in -Adr, but did not enhance glycoge n breakdown (+Adr, glycogen following exercise: 274 +/- 55 mmol (kg dry wt) (-1)) in contracting muscle. 4. The present findings demonstrate that during exercise muscle glycogenoly sis can occur in the absence of adrenaline, and that adrenaline does not en hance muscle glycogenolysis in exercising adrenalectomised subjects. Althou gh adrenaline increases the? glycogen phosphorylase activity it is not esse ntial 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 clue, at least partly, to stimulation by adrenaline.