Testosterone injection stimulates net protein synthesis but not tissue amino acid transport.
Testosterone administration (T) increases lean body mass and muscle protein synthesis. We investigated the effects of short-term T on leg muscle protein kinetics and transport of selected amino acids by use of a model based on arteriovenous sampling and muscle biopsy. Fractional synthesis (FSR) and breakdown (FBR) rates of skeletal muscle protein were also directly calculated. Seven healthy men were studied before and 5 days after intramuscular injection of 200 mg of testosterone enanthate. Protein synthesis increased twofold after injection (P < 0.05), whereas protein breakdown was unchanged. FSR and FBR calculations were in accordance, because FSR increased twofold (P < 0.05) without a concomitant change in FBR. Net balance between synthesis and breakdown became more positive with both methodologies (P < 0.05) and was not different from zero. T injection increased arteriovenous essential and nonessential nitrogen balance across the leg (P < 0.05) in the fasted state, without increasing amino acid transport. Thus T administration leads to an increased net protein synthesis and reutilization of intracellular amino acids in skeletal muscle.
Ferrando
A A
AA
Department of Surgery, University of Texas Medical Branch, Galveston, Texas 77550, USA.
Tipton
K D
KD
Doyle
D
D
Phillips
S M
SM
Cortiella
J
J
Wolfe
R R
RR
D000328:Adult; D000409:Alanine / Q000378:metabolism; D000596:Amino Acids / Q000097:blood / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002247:Carbon Isotopes; D005263:Femoral Artery; D006801:Humans; D007273:Injections, Intramuscular; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008239:Lysine / Q000378:metabolism; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism*; D009587:Nitrogen Isotopes; D010649:Phenylalanine / Q000378:metabolism; D014176:Protein Biosynthesis; D012039:Regional Blood Flow; D012044:Regression Analysis; D013739:Testosterone / Q000008:administration & dosage / Q000494:pharmacology* / Q000502:physiology; D013997:Time Factors; D014316:Tritium
D000596:Amino Acids; D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D014316:Tritium; D013739:Testosterone; D010649:Phenylalanine; D007930:Leucine; D008239:Lysine; D000409:Alanine