No effect of growth hormone administration on substrate oxidation during exercise in young, lean men

TY - JOUR

T1 - No effect of growth hormone administration on substrate oxidation during exercise in young, lean men

AU - Hansen, Mette

AU - Morthorst, Rikke

AU - Larsson, Benny

AU - Dall, Rolf

AU - Flyvbjerg, Allan

AU - Rasmussen, Michael Højby

AU - Orskov, Hans

AU - Kjaer, Michael

AU - Lange, Kai Henrik Wiborg

PY - 2005/9/15

Y1 - 2005/9/15

N2 - The purpose of this study was to examine the effects of increased fat availability induced by growth hormone (GH) administration on the oxidative metabolism during exercise. Seven well-trained males (age 25 +/- 2 years (mean +/- S.E.M.); peak oxygen consumption : 62 +/- 1 ml min(-1) kg(-1) (completed four randomised trials: 120 min bicycling at 55% 4 h after receiving either 7.5 IU (2.5 mg) GH or placebo (Plc), and during rest after receiving either GH or Plc. In all studies a standardized meal was given 2 h after GH or Plc injection. GH administration resulted in an approximately 60-fold increase in serum GH concentration at rest (P < 0.0001) and during exercise (P < 0.0001). The increase in serum GH was followed by an increase in circulating glycerol at rest (8%, P < 0.0001). When combined with exercise the increase in plasma glycerol was more pronounced (GH: 716% of baseline versus Plc: 328%, P < 0.0001). However, this increase in fat mobilization did not increase fat oxidation during exercise (indirect calorimetry). In conclusion, GH administration combined with aerobic exercise increased lipolytic parameters substantially more than exercise alone, but did not further augment whole body fat oxidation.

AB - The purpose of this study was to examine the effects of increased fat availability induced by growth hormone (GH) administration on the oxidative metabolism during exercise. Seven well-trained males (age 25 +/- 2 years (mean +/- S.E.M.); peak oxygen consumption : 62 +/- 1 ml min(-1) kg(-1) (completed four randomised trials: 120 min bicycling at 55% 4 h after receiving either 7.5 IU (2.5 mg) GH or placebo (Plc), and during rest after receiving either GH or Plc. In all studies a standardized meal was given 2 h after GH or Plc injection. GH administration resulted in an approximately 60-fold increase in serum GH concentration at rest (P < 0.0001) and during exercise (P < 0.0001). The increase in serum GH was followed by an increase in circulating glycerol at rest (8%, P < 0.0001). When combined with exercise the increase in plasma glycerol was more pronounced (GH: 716% of baseline versus Plc: 328%, P < 0.0001). However, this increase in fat mobilization did not increase fat oxidation during exercise (indirect calorimetry). In conclusion, GH administration combined with aerobic exercise increased lipolytic parameters substantially more than exercise alone, but did not further augment whole body fat oxidation.

KW - Adipose Tissue/metabolism

KW - Adolescent

KW - Adult

KW - Blood Glucose

KW - Carbohydrate Metabolism

KW - Cross-Over Studies

KW - Double-Blind Method

KW - Exercise/physiology

KW - Fatty Acids, Nonesterified/blood

KW - Glycerol/blood

KW - Human Growth Hormone/blood

KW - Humans

KW - Lactic Acid/blood

KW - Male

KW - Oxidation-Reduction

U2 - 10.1113/jphysiol.2005.089524

DO - 10.1113/jphysiol.2005.089524

M3 - Journal article

C2 - 16002451

SN - 0022-3751

VL - 567

SP - 1035

EP - 1045

JO - The Journal of Physiology

JF - The Journal of Physiology

IS - Pt 3

ER -