Muscle triacylglycerol and hormone-sensitive lipase activity in untrained and trained human muscles

Abstract

During exercise, triacylglycerol (TG) is recruited in skeletal muscles. We hypothesized that both muscle hormone-sensitive lipase (HSL) activity and TG recruitment would be higher in trained than in untrained subjects in response to prolonged exercise. Healthy male subjects (26 +/- 1 years, body moss index 23.3 +/- 0.5 kg m(-2)), either untrained (N = 8, VO(2max) 3.8 +/- 0.2 l min(-1)) or trained (N = 8, VO(2max) 5.1 +/- 0.1 l min(-1)), were studied. Before and after 3-h exercise (58 +/- 1% VO(2max)), a biopsy was taken. Muscle citrate synthase (32 +/- 2 vs. 47 +/- 6 mumol g(-1) min(-1) d.w.) and beta-hydroxy-acyl-CoA-dehydrogenase (38 +/- 3 vs. 52 +/- 5 mumol g(-1) min(-1) d.w.) activities were lower in untrained than in trained subjects (p < 0.05). Throughout the exercise, fat oxidation was higher in trained than in untrained subjects (p < 0.05). Muscle HSL activity was similar at rest (0.72 +/- 0.08 and 0.74 +/- 0.03 mU mg(-1) protein) and after exercise (0.71 +/- 0.1 and 0.68 +/- 0.03 mU mg(-1) protein) in untrained and trained subjects. At rest, the chemically determined muscle TG content (37 +/- 8 and 26 +/- 5 mmol g(-1) d.w.) was similar (p > 0.05), and after exercise it was unchanged in untrained and lower (p < 0.05) in trained subjects (41 +/- 9 and 10 +/- 2 mmol g((1) d.w.). Determined histochemically, TG was decreased (p < 0.05) after exercise in type I and II fibres. Depletion of TG was not different between fibre types in untrained, but tended to be higher (p = 0.07) in type I compared with type II fibres in trained muscles. In conclusion, HSL activity is similar in untrained and trained skeletal muscles both before and after prolonged exercise. However, the tendency to higher muscle TG recruitment during exercise in the trained subjects suggests a difference in the regulation of HSL or other lipases during exercise in trained compared with untrained subjects.

Adipose triglyceride lipase in human skeletal muscle is upregulated by exercise training

“…HSL protein expression was not changed by exercise training in the present study, which was supported by findings in a study in rodents in which HSL protein expression was not different in skeletal muscle of swim-trained rats compared with sedentary controls (10). Furthermore, muscle HSL activity was similar at basal (rest) in untrained and trained male subjects and no differences were seen in IMTG between the two groups (18).…”

“…It is not known whether ATGL protein expression in skeletal muscle might be affected by physical activity, but a hypothesis could be that changes in muscle activity would induce changes in ATGL protein expression like many other proteins (19). An increased ATGL expression with endurance training might be expected since some (18,20,36) but not all (1, 26) endurance training studies have indicated that utilization of IMTG during exercise is enhanced in the endurancetrained state. This increased lipolytic capacity does not seem to relate to changes in HSL protein expression, since HSL protein levels are not changed by endurance training in rat skeletal muscle (10) and in human subjects HSL content is similar in untrained and trained skeletal muscle (18).…”

“…An increased ATGL expression with endurance training might be expected since some (18,20,36) but not all (1,26) endurance training studies have indicated that utilization of IMTG during exercise is enhanced in the endurancetrained state. This increased lipolytic capacity does not seem to relate to changes in HSL protein expression, since HSL protein levels are not changed by endurance training in rat skeletal muscle (10) and in human subjects HSL content is similar in untrained and trained skeletal muscle (18). HSL activity is regulated by phosphorylation on at least five serine sites (47), four of which have been found to be phosphorylated on human skeletal muscle HSL (39,40,50).…”

Human skeletal muscle ceramide content is not a major factor in muscle insulin sensitivity

“…Serial transverse muscle sections were cut from the embedded muscle tissue and then stained for myofibrillar ATPase to identify fibre type composition [18]. Muscle triacylglycerol content was analysed as previously described [19,20].…”

Are substrate use during exercise and mitochondrial respiratory capacity decreased in arm and leg muscle in type 2 diabetes?

“…Muscle glycogen content was analysed by the hexokinase method [24]. Muscle triacylglycerol (TG) content was analysed as described elsewhere [25]. Fibre type, size and capillary density were analysed as described elsewhere [26][27][28].…”