Effects of dynamic exercise intensity on the activation of hormone-sensitive lipase in human skeletal muscle

Abstract

It has been proposed that hormone-sensitive lipase (HSL) regulates intramuscular triacylglycerol hydrolysis in skeletal muscle. The primary purpose of this study was to examine the early activation of HSL and the changes in the putative intramuscular and hormonal regulators of HSL activity at various aerobic exercise intensities. Eight male subjects cycled for 10 min at power outputs corresponding to 30, 60 and 90 % peak oxygen uptake (VO(2,peak)). Muscle samples were obtained at rest and following 1 and 10 min of exercise. Intramuscular triacylglycerol (mean +/- S.E.M.: 24.3 +/- 2.3 mmol (kg dry mass (DM))(-1)), long-chain fatty acyl CoA (13.9 +/- 1.4 micromol (kg DM)(-1)) and HSL activity (1.87 +/- 0.07 mmol min(-1) (kg DM)(-1))) were not different between trials at rest. HSL activity increased at 1 min of exercise at 30 and 60 % VO(2,peak), and to a greater extent at 90 % VO(2,peak). HSL activity remained elevated after 10 min of exercise at 30 and 60 % VO(2,peak), and decreased at 90 % VO(2,peak) from the rates observed at 1 min (1 min: 3.41 +/- 0.3 mmol min(-1) (kg DM)-1; 10 min: 2.92 +/- 0.26 mmol min(-1) (kg DM)(-1)), P < 0.05). There were no effects of exercise power output or time on long-chain fatty acyl CoA content. At 90 % VO(2,peak), skeletal muscle contents of ATP and phosphocreatine were decreased (P < 0.05), and free ADP and free AMP were increased (P < 0.05) during exercise. No changes in these metabolites occurred at 30 % VO(2,peak) and only modest changes were observed at 60 % VO(2,peak). Plasma adrenaline increased (P < 0.05) during exercise at 90 % VO(2,peak) only. These data suggest that a factor related to the onset of exercise (e.g. Ca2+) activates HSL early in exercise. Given the activation of HSL early in exercise, at a time when intramuscular triacylglycerol hydrolysis and fat oxidation are considered to be negligible, we propose that the control of intramuscular triacylglycerol hydrolysis is not solely related to the level of HSL activation, but must also be regulated by postactivational factors.

Figure 1. Hormone-sensitive lipase (HSL) activity at rest and during 10 min of exercise at various power outputs

Exercise was performed at 30, 60 and 90 % peak oxygen uptake (V̇_O2,peak). Values are presented as means ± s.e.m. (n = 8). dm = dry mass. * Significantly different from the resting value of the same trial, P < 0.05; † significant difference from 30 and 60 % V̇_O2,peak at the corresponding time point, P < 0.05; # significantly different from the value measured at 10 min for the same trial, P < 0.05.

Figure 2. Long-chain fatty acyl CoA (LCFA-CoA) at rest and during 10 min of exercise at various power outputs

Exercise was performed at 30 (•), 60 (○) and 90 % (▾) peak oxygen uptake (V̇_O2,peak). Values are presented as means ± s.e.m. (n = 6).

Figure 3. Plasma adrenaline at rest and during 10 min of exercise at various power outputs

Values are presented as means ± s.e.m. (n = 8). *Significant difference from 0 min of the same trial; † significant difference from 30 and 60 % V̇_O2,peak at the corresponding time point, P < 0.05; § significant difference from 1 min of the same trial (P < 0.05).

Figure 4. Plasma insulin at rest and during 10 min of exercise at various power outputs

Values are means ± s.e.m. (n = 8). * Significant difference from 0 min of the same trial; ‡ significant difference from 30 % V̇_O2,peak at a given time; §significant difference from 1 min of the same trial (P < 0.05).