Growth Hormone Jacks Up Protein Synthesis

There’s a debate among academics on whether growth hormone (GH) has any real anabolic effects. Athletes who use GH say the current science stinks because the dosage used in studies is too low and the duration of use is too short. Sound familiar? This was the primary criticism heaped on the old studies on androgens (anabolic steroids). It wasn’t until 1996 that someone did a study in which a “real” dose was given— and shown to be anabolic. Fast forward to the present. Is the issue with GH primarily a dose-dependent one? Let’s see what my fellow science nerds have to say.

The GKT School of Medicine in the United Kingdom did a four-week study in which high-dose recombinant growth hormone (r-GH) was administered daily to male endurance athletes at a dose of 0.067 milligrams per kilogram of body weight.  Whole body leucine turnover was measured at rest and during and after exercise. The researchers found that under resting conditions, GH administration increased the rate of leucine appearance (measure of protein breakdown) and non-oxidative leucine disposal (a measure of protein synthesis) and reduced leucine oxidation (thus, less was used as fuel). This effect was present at week one and even accentuated by week four. During and after exercise, GH decreased the level of leucine oxidation, suggesting an anti-catabolic effect. 

The net result? GH administration, when given in sufficiently high doses, can exert an anabolic effect. This study was performed using male endurance athletes. Imagine if you had these guys lifting weights and eating properly. You’d probably see measurable changes in gross measures such as body composition (lean body mass) and strength.

GH Kicks Myostatin’s Behind
Okay, now that I’ve convinced you that Britney does have a better behind than Christina… oops, wrong column. Now that I’ve convinced you that growth hormone may indeed have anabolic effects, assuming a sufficiently high dose, here’s another intriguing reason why GH may be a favorite with athletes (besides the difficulty in detecting its use). A study from the University of Toronto looked at the in vitro (test tube) and in vivo (whole living animals) effects of GH in 12 GH-deficient hypopituitary subjects given r-GH. They received a dose of five micrograms (mcg) per kilogram of body weight daily in a double-blind, placebo-controlled fashion. 

Note that this dose is much less than the study cited above (67 mcg versus five mcg). Remember that these subjects are GH deficient. So what the researchers are really doing is perhaps bringing the subjects back to “normal” levels. 

The subjects were treated with GH for 18 months. Myostatin mRNA levels decreased by 31 percent compared to the placebo. This inhibitory effect on myostatin was sustained after 12 and 18 months of GH administration. Further, these effects were associated with increases in lean body mass and improved aerobic power. In concurrent in vitro studies, GH-treated skeletal muscle cells had a reduced expression of myostatin. 
What does all this mean? Clearly, we know that if you take enough GH, you’ll realize gains in muscle mass (not to mention its fat-burning or lipolytic effects). Furthermore, we now know that GH targets the myostatin gene by turning off its expression. If you downregulate myostatin, you should realize gains in muscle mass. 

The Special Amino Acids
Do you remember way back when (‘70s and ‘80s) when bodybuilders would gobble amino acid pills like they were M&Ms? Scientists scoffed at them; doctors said they were wasting their money; dietitians said their pee-pee would be expensive. Once again, athletes were one step ahead of the so-called experts. Let’s examine a couple of very cool investigations.

In a study by the Department of Veterans Affairs Medical Center in Omaha, Neb., the following amino acids were found to have a significant anti-catabolic effect: isoleucine, leucine, tyrosine, phenylalanine, tryptophan, lysine and arginine.  Of those, leucine, tyrosine and phenylalanine had a substantial effect at normal serum concentrations. So clearly, leucine, tyrosine and phenylalanine can promote a net anabolic effect via their inhibition of proteosomes.

Another study from the best lab in the business (for investigation of protein/amino acid metabolism) found that human muscle protein synthesis is modulated by extracellular concentrations of amino acids, not intramuscular levels.   This seems sort of bass ackwards, but it’s true. The idea of “bathing” your blood in amino acids by eating frequent high protein/amino acid meals every two to three hours makes sense. That is, if you’re interested in gaining muscle protein.

Ribose Revisited
Just when you thought ribose disappeared into the morass of supplements that might work but are too expensive, here’s a new study that sheds light on this intriguing sugar. Human subjects performed cycle training (15 x 10 seconds of all-out sprinting twice per day for seven days) and received either placebo or ribose (0.2 grams per kilogram of body weight) three times daily. That dose is equal to a total of 54.5 grams of ribose per day. So, if you’re wondering why that two- to five- gram dose of ribose you were taking felt like a placebo, well… you’re right; like many supplements, dose is paramount.

Immediately after the last training session, ATP concentrations in muscle were 22-25 percent lower in placebo and ribose groups (no difference between them). After 72 hours, ATP had returned to baseline levels in the ribose group but was still depressed in the placebo group. The authors of the study concluded that “the availability of ribose in the muscle is a limiting factor for the rate of resynthesis of ATP.” 

So there you have it. Ribose can help you re-synthesize ATP. But you’ve just gotta take a big whopping dose.