Effect of testosterone on the rate of myofibrillar protein breakdown in castrated and adrenalectomized male rats measured by the urinary excretion of 3-methylhistidine

Transcriptional regulation of myotrophic actions by testosterone and trenbolone on androgen-responsive muscle

Androgens regulate body composition and skeletal muscle mass in males, but the molecular mechanisms are not fully understood. Recently, we demonstrated that trenbolone (a potent synthetic testosterone analogue that is not a substrate for 5-alpha reductase or for aromatase) induces myotrophic effects in skeletal muscle without causing prostate enlargement, which is in contrast to the known prostate enlarging effects of testosterone. These previous results suggest that the 5α-reduction of testosterone is not required for myotrophic action. We now report differential gene expression in response to testosterone versus trenbolone in the highly androgen-sensitive levator ani/bulbocavernosus (LABC) muscle complex of the adult rat after 6weeks of orchiectomy (ORX), using real time PCR. The ORX-induced expression of atrogenes (Muscle RING-finger protein-1 [MuRF1] and atrogin-1) was suppressed by both androgens, with trenbolone producing a greater suppression of atrogin-1 mRNA compared to testosterone. Both androgens elevated expression of anabolic genes (insulin-like growth factor-1 and mechano-growth factor) after ORX. ORX-induced increases in expression of glucocorticoid receptor (GR) mRNA were suppressed by trenbolone treatment, but not testosterone. In ORX animals, testosterone promoted WNT1-inducible-signaling pathway protein 2 (WISP-2) gene expression while trenbolone did not. Testosterone and trenbolone equally enhanced muscle regeneration as shown by increases in LABC mass and in protein expression of embryonic myosin by western blotting. In addition, testosterone increased WISP-2 protein levels. Together, these findings identify specific mechanisms by which testosterone and trenbolone may regulate skeletal muscle maintenance and growth.

Urinary excretion of 3-methylhistidine as an index of protein nutrition in total parenteral nutrition

In 39 healthy adult volunteers and nine patients receiving total parenteral nutrition (TPN), determinations were made of the urinary excretion of 3-methylhistidine (3-Mehis) to estimate the degree to which the urinary output of 3-Mehis reflects the status of protein nutrition. In 19 males and 10 females of the former group, measurements were made of the amount of 3-Mehis and of creatinine (Cr) in 24-hr urine samples. The urinary output of 3-Mehis was also measured in two subgroups of five healthy adult male subjects who were fed one of the two different diets prescribed: meat (M) and meat-free (F) diet. Furthermore, in one of these subgroups which was fed on F diet, the urinary output of 3-Mehis was measured both while the subject was kept at bed rest and while the subject was allowed to live a normal life. From these measurements the standard value was determined for the urine 3-Mehis level and the 3-Mehis/Cr ratio in 24-hr urine in healthy adult human subjects of both sexes. In nine patients maintained on TPN these indices of nutritional status were measured before and at 4 weeks of TPN. The time course of the indices was also investigated. The results obtained suggest that both the urinary output of 3-Mehis and the 3-Mehis/Cr ratio can provide a sensitive index of the status of protein nutrition.