Anabolic Effects Of Clenbuterol Research Articles

Acute clenbuterol overdose resulting in supraventricular tachycardia and atrial fibrillation

We are presenting a case illustrating the complex metabolic and rhythm disturbances associated with acute clenbuterol intoxication. Clenbuterol is a long-acting beta2-adrenergic agonist primarily used in veterinary medicine in the United States. It has become a common drug of abuse by body builders because of its reported anabolic and lipolytic properties. In this case report, a body builder using veterinary clenbuterol developed significant electrolyte and cardiac manifestations. A 31-year-old man presented to the emergency department approximately 30 minutes after ingesting 1.5 ml (a tenfold dosing error) of Ventipulmin syrup (72.5 mcg/ml clenbuterol HCl). The product was brought to the emergency department (ED) by the patient. He reported no current use of anabolic steroids. He presented in an anxious state with complaints of palpitations and shortness of breath. Vital signs upon examination were as follows: BP, 122/77 mmHg (16.3/10.3 kPa); HR 254 bpm; RR, 22 bpm; Temperature, 97.1 degrees F (36 degrees C); and oxygen saturation, 100% on ambient air. His electrocardiogram (ECG) demonstrated supraventricular tachycardia with a ventricular rate of 254 bpm. Esmolol was recommended for rate control after the unsuccessful use of adenosine and diltiazem. Laboratory studies showed potassium, 2.1 mmol/L; magnesium, 1.3 mg/dL (0.54 mmol/L); phosphorus, 1.0 mg/dL (0.32 mmol/L); serum glucose, 209 mg/dL (11.6 mmol/L); creatinine, 0.8 mg/dL (70.7 micromol/L); AST, 20 U/L; ALT, 55 U/L; hemoglobin, 12.6 g/dL (126 g/L); CPK total, 87 U/L; and troponin I, 0.23 mug/L. The patient's urine was negative for any drugs of abuse. Clenbuterol levels were not obtained. A second ECG, 16 hours post ingestion, reflected atrial fibrillation with a ventricular rate of 125 to 147 bpm. On hospital day 3, he was electively cardioverted to sinus rhythm; heart rate and rhythm returned to normal, and he was discharged with oral metoprolol. Clenbuterol is approved for use in countries outside the U.S. as a bronchodilator for the treatment of acute asthma exacerbations in humans. Although clenbuterol is not a steroid hormone, it possesses anabolic properties that increase muscle mass. Its longer duration of action compared to other beta2-agonists (such as albuterol) make it a desired agent for body-building because of its high and prolonged serum level. The mechanism for the short and long-term cardiovascular complications of clenbuterol is complex. The anabolic effects of clenbuterol are associated with its beta2-adrenoreceptor agonist activity on striated skeletal muscles. In addition, clenbuterol promotes lipolysis through adipocyte beta3-adrenoreceptors. Considering the significant number of body-building enthusiasts, physicians will continue to encounter clenbuterol abuse in their clinical practices.

Clenbuterol in amyotrophic lateral sclerosis. No indication for a positive effect

The anabolic effects of clenbuterol have been recognized for a long time. Clenbuterol augments the expression of specific muscle proteins with a differential effect on type I and type II fibres. Furthermore, clenbuterol induces the synthesis of endogenous nerve growth factor (NGF) and may itself be a myotrophic factor released by neuron endings. Side effects include tremor and headache and dose dependent abnormalities of laboratory values (hypokalemia, hypoglycemia). After long-term medication increasing fatigue of muscles has been observed. Decreased expression of beta 2-adrenergic receptors may limit the expected functional improvement. The efficacy of clenbuterol as symptomatic treatment of amyotrophic lateral sclerosis has not been proved. Controlled treatment trials are warranted to assess this question.

Effects of clenbuterol and salbutamol on tissue rubidium uptake in vivo

In anesthetized rats, injection of the β 2-adrenoceptor (β 2-AR) agonist clenbuterol (0.45 μmol/kg) caused a marked stimulation of 86RbCl (Rb) uptake by skeletal muscle, but had no effect on other tissues; soleus muscle showed the largest (144% increase) response. Injection of another β 2-AR agonist (salbutamol 0.45 μmol/kg) had no effect on Rb uptake by any tissue except soleus muscle (83%). Both agonists increased body (colonic) temperature to the same extent. A 3-day treatment with salbutamol as a dietary admixture had no effect on body weight, muscle mass, or tissue Rb uptake, whereas the same treatment using clenbuterol produced significant increases in body weight and muscle mass and significant decreases in Rb uptake in three of the four muscle groups studied; Rb uptake in soleus was not affected. In another experiment, the short-term effect of clenbuterol injection on muscle Rb uptake was found to be resistant to a high dose (20 mg/kg) of the selective β 2-AR antagonist ICI 118551. It was concluded that the selective effects of short-term administration of clenbuterol on muscle Rb uptake, coupled with its effects over 3 days on Rb uptake and muscle hypertrophy, implicate β-AR modulation of cation transport (possibly via Na,K-adenosine triphosphatase [ATPase] activity) in the anabolic effects of clenbuterol on muscle protein deposition. Since the stimulation of Rb uptake by clenbuterol was resistant to high doses of a selective β 2-AR antagonist and since salbutamol had little or no effect on muscle hypertrophy or Rb uptake, it is suggested that clenbuterol may exert its effects via an atypical β-AR.

Anabolic effects of clenbuterol after long-term treatment and withdrawal in the rat

Injection of rats with the β 2-adrenoceptor agonist clenbuterol (1 mg/kg/d for 15 days) stimulated an increase in body weight (9%) and protein (8%) and water (7%) content, but reduced food intake (4%) and epididymal fat pad mass (39%). Nine days after termination of treatment, ex-clenbuterol rats were heavier (5%) and had a greater protein (7%) and water (6%) content and lower fat pad mass (32%) than controls. Clenbuterol-fed rats (2 mg/kg diet for 10 days, providing an average of 0.04 mg clenbuterol/kg/d) increased body weight (7%), muscle mass (15% to 21%), and muscle protein content (9% to 26%), whereas epididymal fat pad weight and muscle glycogen content were reduced. During the withdrawal period, the greater body weight of ex-clenbuterol rats was sustained overall (ANOVA, P < .00005), but by day 10 this difference was no longer significant. At this point, gastrocnemius muscle mass was still higher (11%) when compared with that of control animals, but soleus muscle mass, muscle glycogen concentration, and epididymal fat pad weight had reverted to control values. These results were corroborated in a subsequent experiment using older rats. It was concluded that, unlike other β-adrenoceptor-mediated effects, muscle protein accumulated during clenbuterol treatment can be maintained in certain muscles after removal of the drug for a period of time that is at least equivalent to the duration of treatment. This could have implications for the potential therapeutic use of this class of compound, and differences in the response observed between muscle types may help to elucidate the mechanisms responsible for the muscle protein deposition induced by clenbuterol.

Effects of digoxin on the anabolic response to clenbuterol

The possible involvement of increased cation exchange in the anabolic response to the β 2-selective adrenergic agonist clenbuterol was investigated using dietary admixtures of clenbuterol and the Na,K-adenosine triphosphatase (ATPase) inhibitor digoxin. In a rat feeding trial to assess the effects on body composition, it was found that the higher of two levels (5 and 30 mg/kg diet) of digoxin had an inhibitory effect on the repartitioning effects (ie, increased body weight and fat-free mass) of clenbuterol (2 mg/kg diet). In two further experiments using 30 and 60 mg digoxin/kg diet, it was found that the anabolic effects of clenbuterol on gastrocnemius muscle protein deposition were inhibited by digoxin, but the effects of clenbuterol on soleus muscle protein were more resistant to inhibition. Given the observed dose-dependent inhibition by digoxin of gastrocnemius muscle protein deposition in the three experiments, it was concluded that at least part of clenbuterol's anabolic actions on skeletal muscle may depend on increased Na,K-ATPase activity. However, different mechanisms or a different time course of Na,K-ATPase activation may occur in different muscle fiber types.

Changes in tissue blood flow and beta-receptor density of skeletal muscle in rats treated with the beta2-adrenoceptor agonist clenbuterol.

Rats injected with the beta2-adrenoceptor agonist clenbuterol (2 mg kg-1 per day) for 18 days gained significantly more weight than controls. Tissue blood flow assessed 24 h after the last injection from the distribution of radiolabelled microspheres was increased in white (5 fold) and brown (3 fold) adipose tissue of clenbuterol-treated rats but was unaffected in kidney, brain and diaphragm, and was reduced by about 80% in skeletal muscle. Acute injection of clenbuterol one hour before measuring blood flow, increased blood flow to brown fat (20 fold) in both treated and control groups. Blood flow to skeletal muscle increased more in the rats treated chronically with clenbuterol (6 fold increase) than in control rats (2 fold increase), but absolute flow rates were still significantly lower in the rats treated chronically with clenbuterol. Skeletal muscle beta-adrenoceptor density and subtype were assessed from ligand binding and displacement studies using [3H]-dihydroalprenolol. Rats treated with clenbuterol for 18 days showed a 50% reduction in beta-receptor density, but the ratio of beta 1/beta 2-receptors was unaffected (15% beta 1/85% beta 2). The results indicate that, although clenbuterol produces acute increases in muscle blood flow, chronic treatment results in lower flow rates immediately (1 h) and 24 h after the previous injection. The attenuated response following chronic treatment is associated with a marked reduction in skeletal muscle beta-adrenoceptor density. The data suggest that any anabolic effects of clenbuterol on muscle which may require, or may be mediated by increases in blood supply, cannot be sustained by chronic treatment. Conversely, blood flow to white and brown adipose tissue would appear to be potentiated by chronic treatment, possibly reflecting increases in lipolytic and/or thermogenic activity.