By Jerry Brainum
Clenbuterol has acquired a near-legendary status among some power athletes. This reputation is is based on the drug's alleged anabolic and fat-burning properties. Although never approved for sale in the United States, clenbuterol is available in other countries under various trade names, including Clenasma, Monores, Norvegan. Prontovent and Spirovent. The drug is sold either in tablet form or as a solution in various concentrations.
Clenbuterol is often mistakenly identified in the popular media as a "steroid". In fact, it is classified as a beta-2 agonist because of its interactions with adrenergic cell receptors, especially beta-2 adrenergic receptors. Since these receptors are involved in bronchodilatation (expansion of the bronchial air passages), the drug is prescribed to help control asthmatic symptoms.
Clenbuterol and similar beta-2 agonists, such as cimatero) and fenoterol, differ from other common beta-2 agonist drugs in that they remain active in the body longer. For example, clenbuterol has a half-life of 27 hours, taking about five days to dear from the body. In contrast the longest-acting beta-2 agonist sold in the United States, salmeterol lasts only about 12 hours.
However, most researchers believe that the longer a drug takes to clear from the body, the higher the risk of side effects. This explains why beta-2 agonists such as clenbuterol have never been approved for sale in the United States. In addition, from the standpoint of asthmatic therapy, the longer-acting beta-2 agonists show no significant therapeutic benefit over existing asthma drugs, so the profit motive for drug companies is also lacking.
CRITTERS ON CLENBUTEROL
Long-acting beta-2 agonists are attractive to athletes for the drugs' putative muscle-building and fat-burning effects. Animal research using various species (e.g., horses, sheep,chickens and cattle) demonstrates that clenbuterol acts as a "repartitioning agent" That is clenbuterol seems to increase the density of type-II muscle fibers (the type most prone to growth in humans) and concomitantly favors bodyfat losses. One study found a 20% gain in muscle coupled with a 20% loss of fat when clenbuterol was given for just eight to 14 days.
Extrapolated to humans, the doses provided in animal research far exceed what any human could safely tolerate. For instance, the average dose range of clenbuterol needed to provide an effective repartitioning response in animals was between 0.33 and two milligrams per kilogram (a kilogram equals 2.2 pounds). The suggested therapeutic dosage to treat asthmatic symptoms in humans is much less. Doses equivalent to those given to the research animals would most likely kill a human.
THE MYSTERY OF CLENBUTEROL
It's uncertain how clenbuterol and similar long-acting beta-2 agonists work to provide anabolic effects. Animals experience a rapid upgrade in muscle-protein synthesis that lasts for only about five days. After that protein synthesis induced by the drug diminishes: then comes decreased muscle-protein degradation, an anticatabolic effect.
A similar scenario occurs with anabolic steroids — an initial increase in muscle-protein synthesis, followed by an extended anticatabolic effect. Both the protein-synthesizing actions and anticatabolic effects of anabolic steroids are known, but how clenbuterol exerts similar activity (in mega-doses) isn't as clearly established.
No formal clinical studies using clenbuterol as an ergogenic agent in humans exist, probably because of the relatively gargantuan dosages needed to produce anabolic effects in test animals. From an anecdotal point of view, most athletes who've taken the drug use it more for its "thermogenic" or fat-burning properties than for its anabolic effects.
However, the beta-cell receptors that clenbuterol interacts with are exquisitely sensitive and are known to "down-regulate" or close up if exposed to concentrated doses of beta-agonist drugs. Athletes often attempt to circumvent this biological limitation by using a "two-days-on, two-days-off" dosing schedule. Even so, the drug usually stops exerting thermogenic effects in as little as two weeks.
NOW, YOU'RE MAKING ME MAD
Clenbuterol is similar in structure to epinephrine, and like epinephrine, clenbuterol can excessively stimulate the heart, resulting in a rapid heartbeat, or tachycardia. Other possible side effects include muscle tremors, heart-rhythm disturbances, headaches and muscle cramps. The latter problem is thought to occur because beta-2 agonist drugs affect potassium distribution in the body.
A few recent inquiries point to a possible behavioral side effect from using beta-2 agonist drugs. An increase in hostility and anger has been observed in men after a down-regulation of beta-adrenergic cell receptors. One study, published in Psychosomatic Medicine (59:481-87, 1997), found that men with decreased cellular adrenergic receptors also showed greater plasma catecholamine (epinephrine) and cortisol responses to anger provocation.
What's curious about this research is that a similar situation - the infamous 'roid rage is reported to occur in some anabolic-steroid abusers. What happens to an athlete taking clenbuterol and anabolic steroids concurrently is still unknown. Could the anger/rage effect be cumulative? And could the danger be compounded further, since investigations have linked increased anger to a higher risk of cardiovascular disease?
The research on clenbuterol isn't completely negative. A study published in Brain Research (717:44-54,1996) found that giving clenbuterol to rats and mice increased a protective brain substance called "nerve growth factor." This effect was especially evident in the hippocampus, a brain area vital to memory storage and intellectual functioning. If this work is reproducible in humans, it may prove that drugs such as clenbuterol might prevent certain types of degenerative brain diseases.
ARE ASTHMA INHALERS ANABOLIC?
Many athletes familiar with clenbuterol might wonder if using commonly available metered-dose asthma-drug inhalers would produce similar responses. It's not unreasonable to assume that such drugs would offer some ergogenic benefits, since they fall into the same beta-2 agonist category as clenbuterol.
The first thing to consider about asthma inhalers is their highly selective distribution. In essence, most of the drug is delivered to the lungs, with some slight spillover into the general blood circulation. Also, the dosage used in such sprays is usually in micrograms — not enough to promote any type of true ergogenic activity.
Despite these notable shortcomings, however, some investigations have confirmed an increase in power in non-asthmatics given asthma inhalers. For example, a 1988 study (Canadian Jouma; or Sports Science. 13:144-48) found that subjects showed improved prolonged exercise performance (lasting more than an hour) after inhaling a commonly available asthma spray drug called albuterol. Most other research has failed to confirm this effect, although a 1992 investigation did find increased power output with the same drug.
A recent report in the journal Medicine and Science in Sports and Exercise (29:1631-36.1997) looked at the effects of another asthma drug inhaler, terbutaline, on 20 elite male athletes from various sports. The drug was used during tow-temperature conditions, which often provoke exercise-induced asthma. The study, however, found no increase in exercise performance in any of the athletes who used the inhaler.
In another case, reported in the Journal of Allergy and Clinical Immunology (99:443-49,1997), a newer type of commonly available asthma inhaler called salmeterol was examined for its ability to increase power output in athletes. Salmeterol is sold commercially as Serevent inhaler and differs from other asthma inhalers because of its extended activity. It binds to beta-cell receptors with an affinity 50 times greater than that of the other most popular asthma inhaler, albuterol. As a result, it lasts twice as long as albuterol (12 hours versus six) in providing increased bronchodilatation.
Any type of beta-2 agonist drug is capable of raising muscle strength by stimulating an influx of calcium into a portion of the muscle called the sarcoplasm. This in turn, leads to an increase in the binding of muscle contractile proteins (actin and myosin), resulting in more potent muscular contraction.
Actually, this process does not usually occur. Regular exercise leads to a release of catecholamines such as epinephrine, which interact with muscle beta-adrenergic receptors. This constant exposure to epinephrine leads to a down-regulation of the muscle receptors (as occurs when drugs such as clenbuterol are used). The result is lowered muscle responsiveness to beta-2 type drugs, such as various asthma inhalers.
The study on salmeterol confirmed the lack of ergogenic or power increases in athletes inhaling this drug in standard doses (two puffs or inhalations). Based on this finding and others discussed above, most asthma inhalers are deemed legal for use in international athletic competition. In contrast, similar drugs, such as clenbuterol are banned.
The main problem with asthma drugs is the same as that typically occurring with clenbuterol — cell-receptor downgrade. Some doctors fear that with continual usage, some asthma inhalers may not work at all thus endangering asthmatics who depend on them. Salmeterol, unlike albuterol, isn't for emergency use anyway; it takes 20-180 minutes to begin opening up the lungs, while albuterol works immediately.
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