Effects of testosterone replacement on muscle mass and muscle protein synthesis in hypogonadal men--a clinical research center study.

Abstract

Testosterone replacement in hypogonadism has long been known to promote nitrogen retention and increase body density, but the mechanisms of nitrogen retention and body composition changes are poorly defined. We measured body composition and muscle protein synthesis in five hypogonadal men before and 6 months after initiating testosterone replacement. Body composition was examined using dual energy X-ray absorptiometry. Muscle mass was estimated both by excretion of creatinine on a meat-free diet and from appendicular mass measured using dual energy X-ray absorptiometry. Muscle protein synthesis was assessed by measuring the increment of [13C]leucine in mixed muscle protein and myosin heavy chain during a continuous infusion of L-[l-13C]leucine. In all subjects there was an increase in fat-free mass (average, 15%; range, 10-22%; P = 0.02) and a decrease in fat mass (-11%; range, -0.4% to -22.0%; P = 0.03). Muscle mass also increased in everybody (mean, 20%; range, 11-32%; P = 0.04) such that 65% of the increase in fat-free mass could be attributed to accretion of muscle. The accumulation of muscle was associated with a 56% (P = 0.015) increase in the fractional synthesis rate of mixed skeletal muscle proteins and a trend toward a similar increase in the fractional synthesis rate of myosin heavy chain (46%; P = 0.098). We conclude that testosterone replacement in hypogonadal men enhanced skeletal muscle mass by stimulating the muscle protein synthesis rate.

Body composition, metabolic syndrome and testosterone in ageing men

“…26 In a further study of hypogonadal men (who had not received testosterone therapy for at least 2 years before enrollment in the trial), 6 months of testosterone treatment was associated with a 15% increase in FFM and a 20% increase in muscle mass. 27 The effects of testosterone administration on FFM in hypogonadal men have been summarized by Bhasin, 28 with increases of 1-5 kg being evident, dependent upon baseline serum testosterone and the dose and duration of the testosterone treatment regimen. The importance of testosterone dose on the magnitude of increase in skeletal muscle was clearly demonstrated in a study of healthy young men with experimentally induced hypogonadism in whom increases in FFM and muscle volume were directly proportional to the dose of testosterone administered and serum testosterone concentration.…”

The Endocrinology of Aging

“…Testosterone has long been known for its anabolic effects (44). It is unknown, however, whether the age-related decline in muscle mass and muscle strength is causatively related to the parallel decrease in free T levels.…”

“…It is unknown, however, whether the age-related decline in muscle mass and muscle strength is causatively related to the parallel decrease in free T levels. Muscle weakness, anemia, lowered bone mass, and mood disturbances rapidly normalize in mid-adult hypogonadal men during T replacement therapy (44). In addition, treatment of eugonadal adult men with pharmacological doses of T increases muscle mass and strength, especially in combination with exercise or weight training (45).…”

Impaired hypertrophy in myoblasts is improved with testosterone administration

“…protein breakdown/catabolism). A potential clinical intervention for promoting a positive net balance in the favour of protein synthesis is Testosterone (T) administration [15,16]. T replacement therapy has been observed to increase muscle strength and mass in various clinical populations including patients with AIDS, COPD and sarcopenia [12,[17][18][19][20].…”