Enhancement of muscle mitochondrial function by growth hormone.
BACKGROUND
Although GH promotes growth and protein anabolism, which are ATP-dependent processes, the GH effect on mitochondrial regulation remains to be determined.


OBJECTIVE
Our objective was to determine the acute effect of GH on mitochondrial oxidative capacity in skeletal muscle of healthy subjects.


METHODS
The study was a randomized crossover design at an academic medical center.


METHODS
Nine healthy men and women completed the study.


METHODS
GH (150 microg/h) or saline was infused for 14 h on separate days, and muscle biopsies were obtained.


METHODS
Outcome measures included mitochondrial function, gene expression, and protein metabolism.


RESULTS
The 4-fold increase in plasma GH caused elevations in plasma IGF-I, insulin, glucose, and free fatty acids and a shift in fuel selection, with less carbohydrate (-69%) and leucine (-43%) oxidation and 29% more fat oxidation. Muscle mitochondrial ATP production rate and citrate synthase activity were increased 16-35% in response to GH. GH also resulted in higher abundance of muscle mRNAs encoding IGF-I, mitochondrial proteins from the nuclear (cytochrome c oxidase subunit 4) and mitochondrial (cytochrome c oxidase subunit 3) genomes, the nuclear-derived mitochondrial transcription factor A, and glucose transporter 4. Although GH increased whole-body protein synthesis (nonoxidative disposal of leucine), no effect on synthesis rate of muscle mitochondrial proteins was observed.


CONCLUSIONS
These results demonstrate that acute GH action promotes an increase in mitochondrial oxidative capacity and abundance of several mitochondrial genes. These events may occur through direct or indirect effects of GH on intracellular signaling pathways but do not appear to involve a change in mitochondrial protein synthesis rate.
Short
Kevin R
KR
Endocrinology Research Unit, Mayo Clinic School of Medicine, 5-194 Joseph, 200 First Street SW, Rochester, Minnesota 55905, USA.
Moller
Niels
N
Bigelow
Maureen L
ML
Coenen-Schimke
Jill
J
Nair
K Sreekumaran
KS
D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D001706:Biopsy; D002950:Citrate (si)-Synthase / Q000378:metabolism; D018592:Cross-Over Studies; D005260:Female; D019382:Human Growth Hormone / Q000494:pharmacology*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis / Q000235:genetics; D008297:Male; D008931:Mitochondria, Muscle / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D024101:Mitochondrial Proteins / Q000096:biosynthesis / Q000235:genetics; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
D024101:Mitochondrial Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D000255:Adenosine Triphosphate; D002950:Citrate (si)-Synthase