Exercise Induces a Marked Increase in Plasma Follistatin: Evidence That Follistatin Is a Contraction-Induced Hepatokine
Endocrinology Vol. 152, No. 1 164-171 Jakob Hansen

Follistatin is a member of the TGF-β super family and inhibits the action of myostatin to regulate skeletal muscle growth. The regulation of follistatin during physical exercise is unclear but may be important because physical activity is a major intervention to prevent age-related sarcopenia. First, healthy subjects performed either bicycle or one-legged knee extensor exercise. Arterial-venous differences were assessed during the one-legged knee extensor experiment. Next, mice performed 1 h of swimming, and the expression of follistatin was examined in various tissues using quantitative PCR. Western blotting assessed follistatin protein content in the liver. IL-6 and epinephrine were investigated as drivers of follistatin secretion. After 3 h of bicycle exercise, plasma follistatin increased 3 h into recovery with a peak of 7-fold. No net release of follistatin could be detected from the exercising limb. In mice performing a bout of swimming exercise, increases in plasma follistatin as well as follistatin mRNA and protein expression in the liver were observed. IL-6 infusion to healthy young men did not affect the follistatin concentration in the circulation. When mice were stimulated with epinephrine, no increase in the hepatic mRNA of follistatin was observed. This is the first study to demonstrate that plasma follistatin is increased during exercise and most likely originates from the liver. These data introduce new perspectives regarding muscle-liver cross talk during exercise and during recovery from exercise.

Commenter    |     0 commentaire

Commenter    |     9 commentaires

Echinacea for Treating the Common Cold

Commenter    |     0 commentaire

Effect of Vitamin D Supplementation on Testosterone Levels in Men.
Pilz S, Frisch Horm Metab Res 2010 Dec 10.

The male reproductive tract has been identified as a target tissue for vitamin D, and previous data suggest an association of 25-hydroxyvitamin D [25(OH)D] with testosterone levels in men. We therefore aimed to evaluate whether vitamin D supplementation influences testosterone levels in men. Healthy overweight men undergoing a weight reduction program who participated in a randomized controlled trial were analyzed for testosterone levels. The entire study included 200 nondiabetic subjects, of whom 165 participants (54 men) completed the trial. Participants received either 83 μg (3 332 IU) vitamin D daily for 1 year (n=31) or placebo (n=23). Initial 25(OH)D concentrations were in the deficiency range (<50 nmol/l) and testosterone values were at the lower end of the reference range (9.09-55.28 nmol/l for males aged 20-49 years) in both groups. Mean circulating 25(OH)D concentrations increased significantly by 53.5 nmol/l in the vitamin D group, but remained almost constant in the placebo group. Compared to baseline values, a significant increase in total testosterone levels (from 10.7±3.9 nmol/l to 13.4±4.7 nmol/l; p<0.001), bioactive testosterone (from 5.21±1.87 nmol/l to 6.25±2.01 nmol/l; p=0.001), and free testosterone levels (from 0.222±0.080 nmol/l to 0.267±0.087 nmol/l; p=0.001) were observed in the vitamin D supplemented group. By contrast, there was no significant change in any testosterone measure in the placebo group. Our results suggest that vitamin D supplementation might increase testosterone levels. Further randomized controlled trials are warranted to confirm this hypothesis.

Commenter    |     1 commentaire

Commenter    |     5 commentaires

Heavy resistance exercise training and skeletal muscle androgen receptor expression in younger and older men
Steroids Volume 76, Issues 1-2, January 2011, Pages 183-192 Juha P. Ahtiainen

Effects of heavy resistance exercise on serum testosterone and skeletal muscle androgen receptor (AR) concentrations were examined before and after a 21-week resistance training period. Seven healthy untrained young adult men (YT) and ten controls (YC) as well as ten older men (OT) and eight controls (OC) volunteered as subjects. Heavy resistance exercise bouts (5 × 10 RM leg presses) were performed before and after the training period. Muscle biopsies were obtained before and 1 h and 48 h after the resistance exercise bouts from m.vastus lateralis (VL) to determine cross-sectional area of muscle fibers (fCSA) and AR mRNA expression and protein concentrations. No changes were observed in YC and OC while resistance training led to significant increases in maximal strength of leg extensors (1 RM), fCSA and lean body mass in YT and OT. Acute increases occurred in serum testosterone concentrations due to resistance exercises but basal testosterone remained unaltered. Mean AR mRNA expression and protein concentration remained unchanged after heavy resistance exercise bouts compared to pre-values. The individual pre- to post-training changes in resting (pre-exercise) AR protein concentration correlated with the changes in fCSA and lean body mass in the combined group of YT and OT. Similarly, it correlated with the changes in 1 RM in YT. Although mean AR expression did not changed due to the resistance exercise training, the present findings suggest that the individual changes of AR protein concentration in skeletal muscle following resistance training may have an impact on training-induced muscular adaptations in both younger and older men.

Corrélation entre récepteurs aux androgènes et hypertrophie

Commenter    |     1 commentaire

Neuromuscular and Hormonal Responses to Constant and Variable Resistance Loadings
Medicine & Science in Sports & Exercise: January 2011 - Volume 43 - Issue 1 - pp 26-33
WALKER, SIMON

Methods :

Thirteen young men (age = 28.4 ± 3.7 yr) took part in four loadings (maximal strength and hypertrophic loadings using both constant and variable resistance) in a counterbalanced order. Maximal strength loadings consisted of 15 sets of one repetition at 100% one-repetition maximum, and hypertrophic loadings consisted of five sets of 10 repetitions (initial load of 80% one-repetition maximum). Preloading, immediately postloading, 15 min postloading, and 30 min postloading tests consisted of maximal bilateral isometric leg press, venous blood samples (analyzed for total testosterone, growth hormone, and cortisol), and fingertip blood lactate samples. Concentric force and vastus lateralis, vastus medialis, rectus femoris, and biceps femoris EMG was recorded throughout each loading protocol and analyzed over 20° segments.

Results :

Force and quadriceps EMG was greater from 120° to 180° knee angle (P < 0.05) during variable resistance hypertrophic loadings. Larger increases in concentric quadriceps muscle activation and slower recovery in isometric force and muscle activation were observed during variable resistance hypertrophic loadings. Preloading to postloading serum total testosterone, growth hormone, and cortisol concentration increased during variable resistance hypertrophic loading, whereas during constant resistance loadings, only growth hormone increased (P = 0.051). During 30 min postloading, growth hormone and cortisol concentrations remained elevated after both hypertrophic loadings.

A greater level of neuromuscular fatigue and larger responses in serum hormone concentrations occurred after hypertrophic variable resistance loading. These findings indicate greater fatigability during variable resistance loading and that this fatigability influences acute hormonal responses.

Commenter    |     1 commentaire