Abstract
Long term effect of testosterone (T) deficiency impairs metabolism and is associated with muscle degradation and metabolic disease. The association seems to have a bidirectional nature and is not well understood. The present study aims to investigate the early and unidirectional metabolic effect of induced T changes by measuring fasting amino acid (AA) levels in a human model, in which short-term T alterations were induced. We designed a human model of 30 healthy young males with pharmacologically induced T changes, which resulted in three time points for blood collection: (A) baseline, (B) low T (3 weeks post administration of gonadotropin releasing hormone antagonist) and (C) restored T (2 weeks after injection of T undecanoate). The influence of T on AAs was analyzed by spectrophotometry on plasma samples. Levels of 9 out of 23 AAs, of which 7 were essential AAs, were significantly increased at low T and are restored upon T supplementation. Levels of tyrosine and phenylalanine were most strongly associated to T changes. Short-term effect of T changes suggests an increased protein breakdown that is restored upon T supplementation. Fasting AA levels are able to monitor the early metabolic changes induced by the T fluctuations.
Highlights
In healthy males, catabolic and anabolic processes are in balance throughout the diurnal cycle to maintain muscle mass [1]
Nine out of 15 amino acid (AA) that had significant overall changes were affected by T changes, because they significantly increased with low T and restored upon T supplementation
Branched Chain Amino Acids and Aromatic Amino Acids Significantly Changed by Testosterone
Summary
Catabolic (tissue breakdown) and anabolic (tissue repair) processes are in balance throughout the diurnal cycle to maintain muscle mass [1]. Skeletal muscle is the main source of protein for catabolism during energy shortage, caused by fasting or exercise [2]. Gluconeogenesis can provide energy in catabolic states utilizing amino acids (AAs). Branched Chain Amino Acids (BCAAs) and aromatic AAs have been extensively studied [5,6,7]. The aromatic AAs include tryptophan (Trp), tyrosine (Tyr) and phenylalanine (Phe), of which Phe and Tyr cannot be synthesized or degraded in muscles. They can only be degraded in the liver meaning that Phe and Tyr can be used to monitor the net rate of protein degradation [8]
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