No effect of growth hormone administration on substrate oxidation during exercise in young, lean men.
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.
Institute of Sports Medicine, Copenhagen, Denmark. mh19@bbh.hosp.dk
Mette
M
Hansen
Rikke
R
Morthorst
Benny
B
Larsson
Rolf
R
Dall
Allan
A
Flyvbjerg
Michael Højby
MH
Rasmussen
Hans
H
Orskov
Michael
M
Kjaer
Kai Henrik Wiborg
KH
Lange
D000273:Adipose Tissue / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D001786:Blood Glucose; D050260:Carbohydrate Metabolism; D018592:Cross-Over Studies; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D005990:Glycerol / Q000097:blood*; D019382:Human Growth Hormone / Q000097:blood / Q000494:pharmacology*; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D010084:Oxidation-Reduction
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D019382:Human Growth Hormone; D019344:Lactic Acid; D005990:Glycerol