TESTOSTERONE INJECTION STIMULATES NET PROTEIN-SYNTHESIS BUT NOT TISSUE AMINO-ACID-TRANSPORT

Testosterone administration (T) increases lean body mass and muscle pr otein synthesis. We investigated the effects of short-term T on leg mu scle 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 w ere also directly calculated. Seven healthy men were studied before an d 5 days after intramuscular injection of 200 mg of testosterone enant hate. 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 con comitant change in FBR. Net balance between synthesis and breakdown be came more positive with both methodologies (P < 0.05) and was not diff erent from zero. T injection increased arteriovenous essential and non essential nitrogen balance across the leg (P ( 0.05) in the fasted sta te, without increasing amino acid transport. Thus T administration lea ds to an increased net protein synthesis and reutilization of intracel lular amino acids in skeletal muscle.