Nitric Oxide - More than an vasodilator

Robert F Furchgott, Louis J. Ignarro, and Fend Murad were awarded the Nobel Prize in physiology/medicine in 1998 for their discoveries concerning nitric oxide as a signaling molecule in the cardiovascular system. Always need to give credit to the scientists whom delivered bodybuilders the research to give us longer and better "pumps" in the gym. Before the molecular aspects of nitric oxide (NO) are reviewed, a brief history of how this once thought of dangerous gas (i.e., NO has long been considered exclusively as a toxic air pollutant produced by automobiles and power plants) turned out to give bodybuilders a great pump during their workouts and recently has been reported to be an important factor for muscle hypertrophy. Alfred Nobel invented dynamite, a product in which the explosion-prone nitroglycerin is derived.

When the famed Albert Nobel was taken ill with heart disease, his doctor prescribed him nitroglycerin. Nobel refused to take it, knowing that it caused headache and ruling out that it could eliminate chest pain. In a letter, Nobel wrote: "It is ironical that I am now ordered by my physician to eat nitroglycerin' It has been known since last century that the explosive, nitroglycerin, has beneficial effects against chest pain. However, it would take 100 years until it was clarified that nitroglycerin acts by releasing NO gas.

NO and Skelatal Muscle

Enough of the nostalgia, get on with how NO is going to get me bigger and have a better workout! Among the signaling molecules that have recently been identified as mediators of muscle hypertrophy are: insulin-like growth factor, mechano growth factors, angiotensin II (angiotensin II is necessary for optimal overload-induced skeletal muscle hypertrophy) and now NO. In a recent 2005 research study in the Journal Applied Physiology, researchers reported that NO synthase (NO is synthesized within cells by an enzyme synthase or NOS) was required for upregulation of genes involved in muscle hypertrophy contractile function (i.e. actin and type I myosin heavy chain).

Both actin (the main constituent of the thin filaments of muscle fibers) and type I myosin heavy chain (a protein found in muscle fibers involved in muscle contraction) have been reported to increase during muscle overload mediated muscle hypertrophy, but never before has it been documented that NO may mediate these effects. Researchers used a commonly known method of inducing muscle hypertrophy by using functional overload in rats for 12 days. They compared the control group to a group rats who received nothing to rats that were administered a NO inhibitor called L-NAME. After 12 days of muscle overload, the rats administered L NAME had an approximate 50 percent reduction in muscle protein accumulation compared to the control group with a 45 percent increase. Additionally, after 12 days of overload there was a complete inhibition of actin and type I (slow fiber) myosin heavy chain in the rats that had NO inhibited, but the normal group of rats had a 90 percent increase in skeletal muscle actin mRNA and a 140 percent increase in type I muscle fiber myosin heavy chain mRNA.

Interestingly muscle growth factors such as IGF-1 and mechano-growth factors weren't affected by NO inhibition. If you think increasing muscle hypertrophy isn't enough, another article recently came out showing NO could enhance fat loss. In a recent 2005 issue of Biochemical and Molecular Aspects of Nutrition, Zucker diabetic fatty rats (which is an obese and glucose intolerant rat and therefore mimics human adult-onset diabetes) were administered a dietary supplementation of L-arginine which increases NO production. The L-arginine enhanced supplementation had enhanced NO production as well as enhanced production of four genes responsible for fatty acid oxidation in adipose tissue. In addition, the body weights of arginine-treated rats were 16 percent lower at the end of 10 weeks compared to the control rats.

Arginine supplementation reduced the weight of abdominal adipose tissues by 45 percent!!! So ask any body-builder about NO and they'll give the standard answer: it's a vasodilator. NO is a vasodilator°9 but NO has many other functions in the body including increasing glucose uptake, enhancing fat oxidation, and has many positive cardiovascular effects such as: reducing platelet adherence the vessel wall and reducing the division of cells of vascular smooth muscle, as well as reducing LDL medi-dysfunction of endothelial cells.

NO Biochemistry

Tissue mass is taken into consideration, skeletal muscle produces the greatest amount of NO. Interestingly, red blood cells can release NO as well as Nitric oxide is synthesized from the amino acid L- arginine and oxygen by various nitric oxide synthase (NOS) enzymes. Activity of the NOS isoenzymes is dramatically regulated by calcium. L-argi-nine has some unique properties in that this amino acid is an antioxidant and can reverse the pathobiology of oxidative stress. In addition in patients who have impaired endothehal dysfunction, L-arginine can enhance coronary blood flow, reduce symptoms of chest pain, and improve exercise tolerance.

It seems that if a bodybuilder is on the "sauce" then a NO precursor such as L-arginine or NO supplement might be a beneficial supplement to add to his cycle for its cardioprotective effects. In one study, patients with high cholesterol and high LDL were administered L-arginine. Results of the study concluded that patients with high cholesterol and high LDL had impaired endothelial- dependent vasodilation and that administration of L-arginine can improve vasodilation. In another study, animals that were exposed to (cut off circulation then allow blood flow) had significantly less muscle damage after 6 arginine administration. lschemia/ reperfusion leads to skeletal muscle damage by causing microvessel constriction and edema, which exacerbates cell damage.

During the study, after ischemia/reperfusion NO levels drop below baseline values; however, animals that were administered L-arginine had a significant drop in NO, yet the rate was much slower. L-arginine provided a protective effect in muscle against ischemia/reperfusion injury. NO is a vasodilator on skeletal muscle. Endothelial cell release of NO opposes the vasoconstrictor effects of the hormones norepinephrine, endothelin, angiotensin II and serotonin. Administration of the NO inhibitor L-NAME or a genetic deficient of endothelial NO synthase (NOS) impairs endothelium-dependent vasodilation and increases blood presate sure within the arteries. In addition to improving endothelial function, a NO precursor may help out with increasing lean mass and strength. It has been reported that supplements which enhance NO production taken for five weeks in conjunction with a heavy resistance training protocol increased strength and lean muscle mass com- pared to those taking a placebo.

A Key Component for Getting a Good Pump!

The endothelium has several functions in the body, but one of the most important is regulation of vascular via smooth muscle tone. Smooth muscle is a type of non-striated muscle, found within the "walls" of hollow organs such as blood vessels. Smooth muscle is used to move blood within the body, via contraction; it generally operates "involuntarily:' without nerve stimulation. The endothelium is a critical determinant of muscle blood flow. Before the discovery of NO, scientists knew that the endothelium was releasing substances which caused it to relax and vasodilate, but they didn't know exactly what the chemical was so they named it endothelium-derived relaxing factor (EDRF). EDRF was the tentative name of what was later discovered to be NO. It's released by the vascular endotheli ischemia/reperfusiourn in response to a variety of chemical and physical stimuli. It causes the smooth muscle in the vessel wall to relax, resulting in vasodilation. Anyone in the medical field knows that NO is a lifesaver to many people who are having an acute heart attack. By administering nitroglycerine during a heart attack, it expands blood yes and allows for more blood flow back to the heart. Some of the major diseases and conditions that lead to endothelial dysfunction are: high cho- lesterol/high LDL, obesity, high blood pressure, diabetes, artherosclerosis, high triglycerides and using tobacco.

If you think getting a good muscle pump in the gym is the only a healthy endothelium affects, there's one other muscle affected by a dysfunctional endothelium. If you have a healthy endothelium then you should have no problem "having your soldier salute you" during times of passion.The main link between erectile dysfunction and cardiovascular disease is the vascular endothelium, which has a fundamental role in the regulation of circulation. The formation of nitric oxide is a fun link between the endothelium and erectile function; once the ability to generate nitric oxide has been compromised, erectile dysfunction may ensue. Endothelial cell dysfunction has been shown to precede the formation of atherosclerotic and is common in patients with cardiovascular disease or diabetes.

Erectile dysfunction in diabetic men is correlated with endothelial dysfunction. A reduced nitric oxide activity might provide a unifying normal vascular effects of NO are mainly cardioprotec- tive as NO improves vascular tone, inhibits platelets from sticking to the vessel wall and inhibits smooth mus- cle proliferation. NOS is an enzyme which breaks down the formation of NO from L-arginine into two forms, neuronal NOS (nNOS) and endothelial NOS (eNOS). Both are produced in fast and slow twitch muscles, but nNOS seems to be higher in fast-twitch muscles the nNOS are more pronounced in slow-twitch fibers. Although skeletal muscle contains both nNOS and eNOS, nNOS seems to be produced in a greater quantity than eNOS.

During exercise, both eNOS and nNOS are increased in direct relation to the metabolic demand placed on muscle. As mentioned previously, eNOS and nNOS are expressed in skeletal muscle but in addition, both are upregulated in response to exercise and downregulated with unloading or exercise cessation. An acute bout of exercise has been shown to increase NOS activity by approximately 40 percent NO: A Key Regulator of Vascular Endothelial Growth Factor Several angiogenic growth factors may be involved during exercise, including vascular endothelial growth factor (VEGF). Angiogenesis by definition is the growth of new blood vessels from pre-existing blood vessels. Nothing is freakier than looking at a bodybuilder with low body fat and having veins sticking out of their arms in every direction.

So how do you get all those freak veins going? High-intensity exercise that generates a lot of anaerobic activityl. One study looked at muscle biopsies of athletes who utilized two entirely different metabolic systems. Competitive Olympic weightlifters primarily use the ATP-PC system, while runners use primarily the aerobic system.The weightlifters who performed heavy resistance training in contrast to endurance training didn't have increased capillary density. Instead, as a consequence of fiber hypertrophy induced by muscle overloading, capillary density was decreased in the weightlifters. Make no mistake there's a huge difference between how a bodybuilder trains and a weightlifter trains. A weightlifter uses heavy weight (i.e., 80-95 percent of 1-RM) and has prolonged rest periods (i.e., three to five minutes). Body builders on the other hand have been shown to have increased fiber capillary support due to their high intensity anaerobic training (i.e., 60-85 percent of a 1-RM) and short rest periods (one minute or Iess).

So what's the physiological advantage for bodybuilders having more capillaries? One of the most potent stimulators of capillary growth is hypoxia (i.e., intense anaer aging obic exercise). More muscle capillaries result in enhancing tissue blood flow and exchange of metabolic byprod thin ducts produced during high intensity resistance exercise. Basically, bodybuilders have increased capillary density because during high intensity exercise muscle tissue becomes hypoxic, so repeated training increase in the number of capillaries in muscle so it's a closer distance for red blood cells to travel for oxygen exchange. Angiogenesis is a normal process in growth and development, as well as in wound healing. More blood yes damenta sels to muscle means more nutrient delivery, more oxygen, as well as mitochondrial respiration. It's been well established that one of the key regulators of VEGF gene expression is NO. If you don't have the right amount of NO in your vascular system plaque VEGF is inhibited. When rats are exercised on a treadmill for one hour and administered a NO inhibitor there's an approximate 50 percent decrease in VEGF mRNA. In response to a single exercise session with van explanation. The levels of restricted blood flow, vascular endothelial growth factor is significantly upregulated. In one study, muscle biopsies taken after 45 minutes of one-legged knee-extension exercise performed under conditions of restricted blood flow (approximately 15-20 percent lower) at the same absolute workload resulted in increased VEGF mRNA expression by 178 percent. Interestingly, the level of expression was significantly related with thigh venous lactate levels produced during exercise. Additionally, Breen et. al. documented that one hour of acute submaximal treadmill running promoted a three to fourfold increase in VEGF mRNA. So now it should be coming together how NO is important for angiogene growth of new capillaries. Prolonged delivery of vasodilators can increase muscle capillarity growth. In addition, if NO is inhibited, you inhibit capillary growth. 2 So if you like the up, veiny look, your endotheliurn needs plenty of NO.

NO and Iviuscie Hypertrophy

In addition to the recent 2005 Journal of Applied Physiology study reporting on NO being an important regulator of muscle hypertrophy, other researchers have documented similar findings. Smith et al. reported that muscle overload increased production of NO in muscle, again demonstrating NO is an important regulator of muscle hypertrophy. When rats were exposed to chronic muscle overload, there was a 76 percent increase in musclecross-sectional area of normal rats, however in rats that were administered a NO inhibiting drug, there was only a 39.7 percent increase in muscle cross-sectional area. The author speculated that by inhibiting NO production mechanisms such as reducing glucose/insulin uptake in muscle, reducing total calcium content in muscle and possible reduction of satellite cell activation caused by NO inhibition could have all influenced the results.

These results are in agreement with Wang et al who reported that 22 days of NO inhibition by the drug L-NAME in rats resulted in a severe reduction in walking speed (30- fold reduction in walking velocity), muscle fiber cross-sectional area (40 percent reduction) and muscle mass (40 percent reduction). It could also be that since NO has an effect on blood flow, control of blood flow could mediate control of local growth factors such as insulin and IGF-1, but more importantly NO could contribute to activation of satellite cells. There is an overwhelming amount of research documenting that satellite cells are essential for muscle hypertrophy.

An interesting study was published in the 2000 issue in Molecular Biology of the Cell, which documented NO was an important mediator of satellite cell activation.The research study investigated the impact of NO on satellite cell activation under normal and under conditions in which NO was inhibited by L-NAME (i.e., a NO inhibitor). The study used muscle-induced injury to activate satellite cells and found that the satellite cells were activated by NG. The effects of satellite cells were inhibited by the pharmaco rippe logical drug L-NAMF. So what happened to the satellite cells by inhibition of NOS? The author concluded that since NO regulates repair rejuvenation mechanisms in the cell by inhibiting NO, the satellite cells were unable to remove cellular debris and repair muscle for regeneration, which resulted in the inhibition of new muscle fibers being formed.

Still not convinced? Well here's more!!The release of NOS from stretched muscle fibers or damage leads to the production of nitric oxide, which in turn may activate the release of hepatocyte growth factor (HGF). HGF is a cytokine with various different cellular functions. Specific to skeletal muscle hypertrophy, HGF activates satellite cells and may be responsible for causing satellite cells to migrate to the injured area. Good news for bodybuilders, but scientists are looking at other aspects of research involving the use of NO for therapy in Duchenne muscular dystrophy patients. Duchenne muscular dystrophy (DMD) is one of a group of muscular dystrophies characterized by rapid progression of muscle degeneration that occurs early in life. The gene for DMD, found on the X chromosome, encodes a large protein-dystrophin. Dystrophin is required inside muscle cells for structural support; it's thought to strengthen muscle cells It has been shown that NO has therapeutic effects for patients with DMD as NO reduces muscle injury and decreases serum creatine kinase activity (creatine kinase is a marker for skeletal muscle damage).

The administration of NOS to DMD causes a normalization of muscle. So the proposed mechanism for the actions of NO is that NO has anti-inflammatory and cell protective effects. When skeletal muscle of DM0 patients are analyzed the muscles of these patients show marked reduction of NOS protein expression, the reduction of this key gene for NO production exacerbates muscle inflammation and fiber damage by inflammatory cells. So NO is not only needed for vasodilation, but it seems also necessary for muscle hypertrophy. So now that you're ready to start taking some NO precursors, there are a few other that can contribute to getting a good pump.

Other Metabolic Ingredients Needed for a Good Pump

Skeletal muscle blood flow increases in direct proportion to the metabolic demand placed on it during exercise. Just how much, you ask? Well, during dynamic knee extensions in humans, peak blood flow can increase 20 100-fold above resting levels. In addition, if you want a good pump there's an immediate and rapid increase in blood flow related to the strength of contraction, contraction frequency and speed, and the number of muscle fibers recruited during exercise. So avoid 'super-slow" contractions like the plague and stick to multi-joint exercises that require lots of motor units like squats, bench press, bent-rows, etc. for a good pump.

So why are local substances released during exercise that cause vasodilation of muscle and increased blood flow? The automatic regulation of skeletal muscle blood flow is controlled by the activity of the sympathetic nervous system. During exercise, norepinephrine is released which is a potent vasoconstrictor of vascular smooth muscle. The sympathetic nervous activity increases with the contractile activity of muscle as well as with the muscle mass utilized. Skeletal muscle compensates for this constriction by releasing local vasodilatory substances, which may antagonize actions of the sympathetic nervous system. The vasodilatory response to muscle contraction is rapid. Muscle blood flow increases after the first second of a single contraction and stabilizes within approximately 30 seconds during dynamic exercise.

NO isn't the only locally produced vasodilatory substance produced. Additional factors associated early exercise blood flow may include adenosine, potassium, lactate, changes in pH, prostaglandins and 71.22 acetylcholine. Here's some other little research that might help you get a better pump: stay away from aspirin and other NSAIDs to get the best pump. The prostaglandin prostacyclin and prostaglandin E2 are vasodilators. Infusions of prostacyclin and prostaglandin E2 have both been reported to cause vasodilation in muscle. Both are formed intramuscularly and concentrations of both rise during exercise. One study using a COX inhibitor reported that COX inhibitors reduced exercise blood flow by approximately 20 percent. And finally, here's one study that will definitely make caffeine junkies cry, it seems that adenosine is an important regulator of vasodilation. As you well know, caffeine is an adenosine antagonist.

When healthy volunteers performed five 15-minute work periods at different workloads, adenosine increased with increased work rate. The findings suggest that adenosine increases with exercise intensity and may work in conjunction with other vasodilatory substances such as NO, lactic acid, etc. regulating muscle blood flow. Additionally, the adenosine receptor antagonist theophylline reduced exercise blood flow by approximately 20 percent in humans! In conclusion, L-arginine is a pre-cursor for NO production. Most NO supplements contain L-arginine based precursors along with other metabolic ingredients, which is probably more conducive to getting a good muscle pump than L-arginine alone. L-arginine is found in high concentrations in fish, poultry and beans. Western diets typically contains about three to six grams of arginine per day, however the bioavailability of exogenous arginine is approximately 60 percent.

One might think that eating plenty of protein might provide all the L-arginine you need, but it seems that a NO precursor supplement might be beneficial since 50 to 70 percent of dietary arginine is metabolized by the intestinal mucosa and doesn't enter circulation. It seems that there is extensive catabolism of the amino acid L-arginine in the small intestines, in fact in adults 38 percent of dietary L-arginine is removed in the first pass of the small intestines. L-arginine has an effect on increasing NO production by improving endothelial dependent vasodilation. Other supplements found to increase vasodilation in muscle are fish oils and using low-fat diets. Although NO is just one of many local vasodilators found in muscle, it's not likely that one, but a combination, of vasodilators (i.e., adeno factor sine, potassium, Lactate, changes pH, prostaglandins, and acetylcholine) act together to produce optimal muscle blood flow.

Key Points:

NO is essential for muscle hypertrophy

NO contributes to angiogenesis, VEGF and vasodilation;

NO also increases glucose uptake, enhances fat oxidation and has many positive cardiovascular effects;

NO is stimulated by high intensity exercise with short rest periods;

In addition to NO precursor supplements, perform movements that recruit lots of muscle fibers for a pump.