Clenbuterol ingestion causing prolonged tachycardia, hypokalemia, and hypophosphatemia with confirmation by quantitative levels

Adverse events of clenbuterol among athletes: a systematic review of case reports and case series

Clenbuterol is a potent beta-2 agonist widely misused by professional athletes and bodybuilders. Information on clenbuterol associated adverse events is present in case reports and case series, though it may not be readily available. This systematic review aimed to critically evaluate the evidence of adverse events associated with clenbuterol among athletes. The search strategy was in accordance with PRISMA guidelines. Databases such as PubMed, Science Direct, Scopus, and Google Scholar were searched from 1990 to October 2021 to find out the relevant case reports and case series. There were 23 included studies. Using a suitable scale, the included studies' methodological quality analysis was evaluated. In total, 24 athletes experienced adverse events. Oral ingestion of clenbuterol was the most preferred route among them. The daily administered dose of clenbuterol was ranging from 20 µg to 30 mg. Major adverse events experienced by athletes were supraventricular tachycardia, atrial fibrillation, hypotension, chest pain, myocardial injury, myocarditis, myocardial ischemia, myocardial infarction, cardiomyopathy, hepatomegaly, hyperglycemia, and death. The cardiac-related complications were the most commonly occurring adverse events. Clenbuterol is notorious to produce life-threatening adverse events including death. Lack of evidence regarding the performance-enhancing effects of clenbuterol combined with its serious toxicities questions the usefulness of this drug in athletes.

Meat food fraud risk in Chinese markets 2012-2021

Food fraud is a major concern worldwide, and the majority of cases include meat adulteration or fraud. Many incidences of food fraud have been identified for meat products both in China and abroad over the last decade. We created a meat food fraud risk database compiled from 1987 pieces of information recorded by official circular information and media reports in China from 2012 to 2021. The data covered livestock, poultry, by-products, and various processed meat products. We conducted a summary analysis of meat food fraud incidents by researching fraud types, regional distribution, adulterants and categories involved, categories and sub-categories of foods, risk links and locations, etc. The findings can be used not only to analyze meat food safety situations and study the burden of food fraud but also help to promote the efficiency of detection and rapid screening, along with improving prevention and regulation of adulteration in the meat supply chain markets.

Risk Associated with the Use of Selected Ingredients in Food Supplements

This review focuses on four new product categories of food supplements: pre-workout, fat burner/thermogenic, brain/cognitive booster, and hormone/testosterone booster. Many food supplements have been shown to be contaminated with unauthorized substances. In some cases, the ingredients in the new categories of dietary supplements were medicinal products or new synthetic compounds added without performing clinical trials. Some of the new ingredients in dietary supplements are plant materials that are registered in the pharmacopoeia as herbal medicines. In other cases, dietary supplements may contain plant materials that have no history of human use and are often used as materials to 'camouflage' stimulants. In the European Union, new ingredients of dietary supplements, according to European Food Safety Authority or unauthorized novel food. Furthermore, selected ingredients in dietary supplements may be prohibited in sports and are recognized as doping agents by World Anti-Doping Agency.

Clenbuterol Food Poisoning from Snake Meat Consumption: An Outbreak of 13 Cases

We report a documented outbreak of clenbuterol food poisoning involving 13 patients who consumed snake meat in Shenzhen. They developed headache, palpitation, tachycardia, hypokalaemia and other symptoms within first 3 hours after exposure. They were initially treated with gastric lavage, fluid and potassium replacement and other supportive measures. All of them completely recovered after admission for up to 48 hours. Public health investigation identified clenbuterol compound in four victims' urine and the food source of snake meat they consumed. (Hong Kong j.emerg.med. 2015;22:46-49)

Clenbuterol Attenuates hERG Channel by Promoting the Mature Channel Degradation

Clenbuterol, a β2-selective adrenergic receptor agonist, is illicitly used in weight loss and performance enhancement and animal production. Increasing evidence demonstrates that clenbuterol induces various kinds of arrhythmias and QTc interval prolongation. However, little is known about the underlying mechanism. Most drugs are associated with QTc prolongation through interfering with human ether-a-go-go-related gene (hERG) K⁺ channels. The present study aims to investigate the effects and underlying mechanisms of clenbuterol on the hERG channel. HEK 293 cells were transfected with wild type and Y652A or F656A mutants of the hERG channel and treated with clenbuterol. The hERG current was recorded using whole-cell patch-clamp technique, and protein level was evaluated by Western blot. We found that clenbuterol decreases the mature form of the hERG protein at the cell membrane in a concentration- and time-dependent manner, without affecting the immature form. Correspondingly, clenbuterol chronic treatment reduced hERG current to a greater extent compared to acute treatment. In the presence of Brefeldin A (BFA), which was used to block hERG channel trafficking to cell membrane, clenbuterol reduced hERG on plasma membrane to a greater extent than BFA alone. In addition, the hERG channel's drug binding sites mutant Y652A and F656A abolished clenbuterol-mediated hERG reduction and current blockade. In conclusion, clenbuterol reduces hERG channel expression and current by promoting the channel degradation. The effect of clenbuterol on the hERG channel is related to the drug-binding sites, Tyr-652 and Phe-656, located on the S6 domain. This biophysical mechanism may underlie clenbuterol-induced QTc prolongation or arrhythmia.

Case of low dose clenbuterol toxicity

We present a case of acute clenbuterol toxicity following ingestion of 20 μg of clenbuterol, resulting in symptoms of sympathetic activation, sinus tachycardia and electrolyte derangement. The patient was managed conservatively with fluid resuscitation, electrolyte replacement and monitoring, and discharged following a 5-day stay in hospital.

Phosphate homeostasis and disorders

Recent studies of inherited disorders of phosphate metabolism have shed new light on the understanding of phosphate metabolism. Phosphate has important functions in the body and several mechanisms have evolved to regulate phosphate balance including vitamin D, parathyroid hormone and phosphatonins such as fibroblast growth factor-23 (FGF23). Disorders of phosphate homeostasis leading to hypo- and hyperphosphataemia are common and have clinical and biochemical consequences. Notably, recent studies have linked hyperphosphataemia with an increased risk of cardiovascular disease. This review outlines the recent advances in the understanding of phosphate homeostasis and describes the causes, investigation and management of hypo- and hyperphosphataemia.

Adverse effects from clenbuterol and ractopamine on nematode Caenorhabditis elegans and the underlying mechanism

In the present study, we used Caenorhabditis elegans assay system to investigate in vivo toxicity from clentuberol and ractopamine and the possible underlying mechanism. Both acute and prolonged exposures to clentuberol or ractopamine decreased brood size and locomotion behavior, and induced intestinal autofluorescence and reactive oxygen species (ROS) production. Although acute exposure to the examined concentrations of clentuberol or ractopamine did not induce lethality, prolonged exposure to 10 µg/L of clentuberol and ractopamine reduced lifespan. At relatively high concentrations, ractopamine exhibited more severe toxicity than clentuberol on nematodes. Overexpression of sod-2 gene encoding a Mn-SOD to prevent induction of oxidative stress effectively inhibited toxicity from clentuberol or ractopamine. Besides oxidative stress, we found that clentuberol might reduce lifespan through influencing insulin/IGF signaling pathway; however, ractopamine might reduce lifespan through affecting both insulin/IGF signaling pathway and TOR signaling pathway. Ractopamine more severely decreased expression levels of daf-16, sgk-1, skn-1, and aak-2 genes than clentuberol, and increased expression levels of daf-2 and age-1 genes at the examined concentration. Therefore, the C. elegans assay system may be useful for assessing the possible toxicity from weight loss agents, and clentuberol and ractopamine may induce toxicity through different molecular mechanisms.

Dose-effects of aorta-infused clenbuterol on spinal cord ischemia-reperfusion injury in rabbits

Background

The β₂ adrenergic receptor (β₂AR) plays an important role in ischemia-reperfusion (I/R) injury in various organs. Recently, a selective β₂AR agonist clenbuterol was suggested to protect against cerebral I/R injury. This study was designed to investigate changes of β₂ARs after spinal cord I/R injury and dose-effects of aorta-infused clenbuterol on spinal cord I/R injury in rabbits.

Methods

Spinal cord ischemia was induced in New Zealand white rabbits by infrarenal abdominal aortic occlusion with a balloon catheter for 30 minutes except the sham group. During occlusion, nothing (I/R group), normal saline (NS group) or clenbuterol at different doses of 0.005, 0.01, 0.05, 0.1, 0.5, or 1 mg/kg (C_0.005, C_0.01, C_0.05, C_0.1, C_0.5, and C₁ groups) was infused into the occluded aortic segments. The hemodynamic data, blood glucose and serum electrolytes were measured during experimental period. Neurological function was assessed according to the modified Tarlov scales until 48 hours after reperfusion. After that, the lumbar spinal cord was harvested for β₂AR immunohistochemistry and histopathologic evaluation in the anterior horns.

Results

The β₂AR expression in the anterior horns of the spinal cord was significantly higher in the I/R group than in the sham group. Tarlov scores and the number of viable α-motor neurons were higher in C_0.01-C_0.5 groups than in the NS group, C_0.005 and C₁ groups and were highest in the C_0.1 group. Hypotension and hyperglycemia were found in the C₁ group.

Conclusion

β₂ARs in the anterior horn were upregulated after spinal cord I/R injury. Aortic-infused clenbuterol (0.01–0.5 mg/kg) can attenuate spinal cord I/R injury dose-dependently during the ischemic period. The Optimal dosage was 0.1 mg/kg. Activation of β₂AR could be a new therapeutic strategy for the treatment of spinal cord I/R injury.

Case report and review of clenbuterol cardiac toxicity

Clenbuterol is an oral β2-agonist utilized as an illicit substance for performance-enhancement or weight loss. We report a case of a 23-year-old male who presented with anxiety and chest tightness after intentional ingestion of 5000 μg of clenbuterol (125 times the recommended adult dose) to lose weight. His electrocardiogram showed sinus tachycardia and diffuse nonspecific repolarization abnormalities with mild inferolateral ST-segment depression. Bloodwork revealed a potassium of 2.0 mmol/L, peak lactate of 9.4 mmol/L, and peak troponin of 5.39 μg/L. A transthoracic echocardiogram was normal except for hyperdynamic left ventricular function. He was treated with intravenous fluids and oral metoprolol. His tachycardia and electrocardiogram abnormalities resolved after 48 h. Clenbuterol has gained notoriety in recent years as a drug of abuse and cases of toxicity will likely continue to increase due to its relative attainability and readily accessible online dosing information. Patients often present with agitation, palpitations, tachycardia, hypokalemia, and hyperglycemia. Treatment is supportive with intravenous fluids, β-blockers, and potassium supplementation. <Learning objective: Clenbuterol, an oral β2-agonist, can be utilized as an illicit substance for performance-enhancement or weight loss. Cardiac toxicity and type II myocardial infarction can occur with clenbuterol overdoses. Associated symptoms include agitation, palpitations, tachycardia, hypokalemia, and hyperglycemia. Treatment is supportive primarily with intravenous fluid, β-blockers, and potassium supplementation.>.

Effects of clenbuterol on horses

Clenbuterol was intended as a treatment for respiratory diseases in horses, but has been used in multiple species, including humans, for its repartitioning of fat to lean effects (free fatty acids are released from adipose tissue to be used by tissues of higher priority). In the horse industry clenbuterol application is restricted to the treatment of chronic obstructive pulmonary disease and reactive airway disease (heaves). Negative effects of clenbuterol exposure include a decrease in maximum oxygen intake and increased muscle fatigue upon exercise. As a result of these and other negative effects, clenbuterol remains strictly controlled by the US Food and Drug Administration.

Toxicity of weight loss agents

INTRODUCTION

With the rise of the obesity epidemic in the United States over the last several decades and the medical complications seen with it, weight loss and dieting have become a national public health concern.

DISCUSSION

Because of their increased use and availability through internet sales, several different dieting agents were reviewed for potential toxicity. These included: syrup of ipecac, cathartics, human chorionic gonadotropin hormone, 2,4 Dinitrophenol, guar gum, phenylpropanolamine, ma huang/ ephedra, caffeine, clenbuterol, fenfluramine, sibutramine, thyroid hormone, orlistat and cannabinoid antagonists.

CONCLUSIONS

With the internet making even banned products readily accessible, healthcare providers need to be aware of the potential toxicities of a wide range of weight loss agents. Our review covered topics we thought to be most historically significant as well as pertinent to the practice of medical toxicology today.

Effects of clenbuterol administration on serum biochemical, histologic, and echocardiographic measurements of muscle injury in exercising horses

OBJECTIVE

To determine the effects of clenbuterol, at a dosage of up to 3.2 μg/kg for 14 days, PO, on skeletal and cardiac muscle in healthy horses undergoing treadmill exercise.

ANIMALS

12 healthy horses from 3 to 10 years old.

PROCEDURES

Horses were randomly assigned to a control group (n = 6) or clenbuterol group (6) and received either saline (0.9% NaCl) solution or clenbuterol, PO, every 12 hours for 14 days. Horses were subjected to submaximal treadmill exercise daily during treatment. Muscle biopsy specimens were collected before and after treatment for determination of apoptosis. Echocardiographic measurements, serum clenbuterol and cardiac troponin I concentrations, and serum activities of creatine kinase and aspartate aminotransferase were measured before, during, and after treatment. Jugular venous blood samples were collected every 3 days during treatment. Echocardiography was repeated every 7 days after beginning treatment. Response variables were compared between treatment groups and across time periods.

RESULTS

No significant effect of clenbuterol or exercise on response variables was found between treatment and control groups at any time point or within groups over time.

CONCLUSIONS AND CLINICAL RELEVANCE

Results did not reveal any adverse effects of treatment with an approved dose of clenbuterol on equine cardiac or skeletal muscle in the small number of horses tested.

Beta2 adrenergic agonist, clenbuterol, enhances working memory performance in aging animals

Previous studies using a mixed beta1 and beta2 adrenergic antagonist, propanolol, have indicated that beta adrenoceptors have little effect on the cognitive functioning of the prefrontal cortex. However, recent studies have suggested that endogenous stimulation of beta1 adrenoceptors impairs working memory in both rats and monkeys. Since propanolol has no effect on cognition, we hypothesized that activation of beta2 adrenoceptors might improve performance in a working memory task. We tested this hypothesis by observing the effects of the beta2 agonist, clenbuterol, on spatial working memory performance. Clenbuterol was either infused directly into the prefrontal cortex (rats) or administered systemically (monkeys). Results demonstrated that clenbuterol improved performance in many young and aged rats and monkeys who performed poorly under control conditions. Actions at beta2 adrenoceptors were confirmed by challenging the clenbuterol response with the beta2 adrenergic antagonist, ICI 118,551. The effects of clenbuterol were not universal and depended on the cognitive status of the animal: the drug moderately improved only a subset of animals with working memory impairment.

Acute clenbuterol overdose resulting in supraventricular tachycardia and atrial fibrillation

OBJECTIVE

We are presenting a case illustrating the complex metabolic and rhythm disturbances associated with acute clenbuterol intoxication.

BACKGROUND

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.

CASE REPORT

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.

DISCUSSION

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.

CONCLUSION

Considering the significant number of body-building enthusiasts, physicians will continue to encounter clenbuterol abuse in their clinical practices.

Roles and potential therapeutic targets of the ubiquitin proteasome system in muscle wasting

Muscle wasting, characterized by the loss of protein mass in myofibers, is in most cases largely due to the activation of intracellular protein degradation by the ubiquitin proteasome system (UPS). During the last decade, mechanisms contributing to this activation have been unraveled and key mediators of this process identified. Even though much remains to be understood, the available information already suggests screens for new compounds inhibiting these mechanisms and highlights the potential for pharmaceutical drugs able to treat muscle wasting when it becomes deleterious. This review presents an overview of the main pathways contributing to UPS activation in muscle and describes the present state of efforts made to develop new strategies aimed at blocking or slowing muscle wasting.

Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; ).

Thyrotoxic hypokalemic periodic paralysis: An overlooked pathology in western countries

Thyrotoxic hypokalemic periodic paralysis (THPP) is a complication of hyperthyroidism that is mostly diagnosed in Asian populations; consequently, it can be difficult to recognize in western populations. THPP represents an endocrine emergency that can result in respiratory insufficiency, cardiac arrhythmias, and death. Its differential diagnosis from the other more common forms of hypokalemic paralysis is important to avoid inappropriate therapy. Here, we discuss the main pathogenetic hypotheses, clinical features, and therapies of this disease. We also report an example of THPP management in our primary care unit.

A pharmacodynamic study on clenbuterol-induced toxicity: beta1- and beta2-adrenoceptors involvement in guinea-pig tachycardia in an in vitro model

Beta(2)-receptor adrenergic agonists as clenbuterol and analogues are illegally used as growth promoters in cattle, in Europe, as well as in other countries. Following consumption of meat or liver, intoxication cases were described, and cardiovascular toxic effects (tachycardia, hypertension) were of clinical relevance. Therefore, we investigated whether heart rate increase induced by clenbuterol could depend upon stimulation of beta(1)- and/or beta(2)-adrenergic receptors, and in which ratio. We used in vitro guinea-pig atria, a model in which beta(1)-/beta(2)-receptors ratio is similar to that found in men. In our experiments both beta(1)- and beta(2)-receptors contributed to clenbuterol-induced heart rate increase, but with a different potency. The selective beta(2)-antagonist ICI-118,551 competitively antagonized responses to clenbuterol with high affinity (pA(2) 9.47+/-0.28, SchildSlope 0.98+/-0.20 not significantly different from unity, K(B) 0.34 nM). The selective beta(1)-antagonist atenolol antagonized clenbuterol with a relatively lower affinity (pA(2)=7.59+/-0.14), the SchildSlope=1.97+/-0.33 was significantly different from unity (P<0.05). Results show that clenbuterol stimulates guinea-pig heart rate by acting chiefly on beta(2)-adrenoceptor, although responses to clenbuterol apparently are mediated by an inter-play between both beta-adrenoceptors. Further experiments are necessary to understand which beta-adrenergic antagonists are of effectiveness to counteract cardiovascular effects in case of intoxication following clenbuterol, or other beta-adrenergic stimulants.

Food poisoning by clenbuterol in Portugal

This paper describes the occurrence of four cases of acute food poisoning, involving a total of 50 people, due to the ingestion of lamb and bovine meat containing residues of clenbuterol. Symptoms shown by the intoxicated people may be generally described as gross tremors of the extremities, tachycardia, nausea, headaches and dizziness. Analytical methodology developed for the determination of clenbuterol in meat, liver and blood samples is described. Procedures are described which should be followed when the described symptoms are evident in a group of people who have ingested contaminated meat, and particularly liver of ruminants.

Myocardial Infarction in a 17-Year-Old Body Builder Using Clenbuterol

A case of non-Q myocardial infarction in a previously healthy 17-year-old body builder, who used clenbuterol, a long-acting beta(2) adrenergic agonist with anabolic and lipolytic effects, is reported. Only 1 case report of myocardial infarction associated with the use of clenbuterol was found in a literature review and that case was, however, associated with anabolic steroid use. This is the first case report to describe myocardial infarction in a young male body builder only taking clenbuterol.

Anticachectic effects of formoterol: a drug for potential treatment of muscle wasting

In cancer cachexia both cardiac and skeletal muscle suffer an important protein mobilization as a result of increased proteolysis. Administration of the beta2-agonist formoterol to both rats and mice bearing highly cachectic tumors resulted in an important reversal of the muscle-wasting process. The anti-wasting effects of the drug were based on both an activation of the rate of protein synthesis and an inhibition of the rate of muscle proteolysis. Northern blot analysis revealed that formoterol treatment resulted in a decrease in the mRNA content of ubiquitin and proteasome subunits in gastrocnemius muscles; this, together with the decreased proteasome activity observed, suggest that the main anti-proteolytic action of the drug may be based on an inhibition of the ATP-ubiquitin-dependent proteolytic system. Interestingly, the beta2-agonist was also able to diminish the increased rate of muscle apoptosis (measured as DNA laddering as well as caspase-3 activity) present in tumor-bearing animals. The present results indicate that formoterol exerted a selective, powerful protective action on heart and skeletal muscle by antagonizing the enhanced protein degradation that characterizes cancer cachexia, and it could be revealed as a potential therapeutic tool in pathologic states wherein muscle protein hypercatabolism is a critical feature such as cancer cachexia or other wasting diseases.

Is postural tremor size controlled by interstitial potassium concentration in muscle?

OBJECTIVES

To determine whether factors associated with postural tremor operate by altering muscle interstitial K(+).

METHODS

An experimental approach was used to investigate the effects of procedures designed to increase or decrease interstitial K(+). Postural physiological tremor was measured by conventional means. Brief periods of ischaemic muscle activity were used to increase muscle interstitial K(+). Infusion of the beta(2) agonist terbutaline was used to decrease plasma (and interstitial) K(+). Blood samples were taken for the determination of plasma K(+).

RESULTS

Ischaemia rapidly reduced tremor size, but only when the muscle was active. The beta(2) agonist produced a slow and progressive rise in tremor size that was almost exactly mirrored by a slow and progressive decrease in plasma K(+).

CONCLUSIONS

Ischaemic reduction of postural tremor has been attributed to effects on muscle spindles or an unexplained effect on muscle. This study showed that ischaemia did not reduce tremor size unless there was accompanying muscular activity. An accumulation of K(+) in the interstitium of the ischaemic active muscle may blunt the response of the muscle and reduce its fusion frequency, so that the force output becomes less pulsatile and tremor size decreases. When a beta(2) agonist is infused, the rise in tremor mirrors the resultant decrease in plasma K(+). Decreased plasma K(+) reduces interstitial K(+) concentration and may produce greater muscular force fluctuation (more tremor). Many other factors that affect postural tremor size may exert their effect by altering plasma K(+) concentration, thereby changing the concentration of K(+) in the interstitial fluid.

New beta-adrenergic agonists used illicitly as growth promoters in animal breeding: chemical and pharmacodynamic studies

Clenbuterol and beta-adrenergic receptor agonist drugs are illegally used as growth promoters in animal production. Pharmacologically active residues in edible tissues led to intoxication outbreaks in several countries. Pressure of official controls pulsed synthesis of new compounds to escape analytical procedures. We report two new compounds named 'A' and 'G4', found in feeding stuffs. Chemical structure was studied through nuclear magnetic resonance-imaging and infrared spectroscopy, and beta(1)- and beta(2)-adrenergic activity was evaluated on isolated guinea-pig atrium and trachea in comparison with clenbuterol. Both compounds share with clenbuterol an halogenated aromatic ring with a primary amino group. Main modifications consisted of substitution of secondary amino group with an alkyl chain in compound A and substitution of the ter-butyl group with a benzene ring in compound G4. In guinea-pig trachea these compounds showed myorelaxant potency lower than clenbuterol (EC(50) was 43.8 nM for clenbuterol, 11700 nM for compound A, 2140 nM for G4). On the contrary, in the guinea-pig atrium (heart-beat rate stimulant effect) the compounds were more potent than clenbuterol (EC(50) was 15.2 nM for clenbuterol, 3.4 nM for compound A, 2.8 nM for G4). These pharmacodynamic properties, and stronger lipophilic properties shown by the two compounds may result in increased cardiovascular risk for consumers of illicitly treated animals.