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Beta2 -adrenergic agonist clenbuterol increases energy expenditure and fat oxidation, and induces mTOR phosphorylation in skeletal muscle of young healthy men

Jessen, S, Solheim, SA, Jacobson, GA ORCID: 0000-0002-3409-8769, Eibye, K, Bangsbo, J, Nordsborg, NB and Hostrup, M 2020 , 'Beta2 -adrenergic agonist clenbuterol increases energy expenditure and fat oxidation, and induces mTOR phosphorylation in skeletal muscle of young healthy men' , Drug Testing and Analysis, vol. 12, no. 5 , pp. 610-618 , doi: 10.1002/dta.2755.

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Clenbuterol is a beta2-adrenoceptor agonist marketed as an asthma reliever but isnot approved for human use in most countries due to concerns of adverse cardiaceffects. Given its demonstrated hypertrophic and lipolytic actions in rodents,clenbuterol is one of the most widely abused doping substances amongt athletes andrecreational body-builders seeking leanness. Herein, we examined the effect ofclenbuterol ingestion on metabolic rate as well as skeletal muscle mammalian targetof rapamycin (mTOR) phosphorylation and protein kinase A (PKA)-signaling in sixyoung men. Before and 140 min after ingestion of 80 μg clenbuterol, resting metabolic rate and contractile function of the quadriceps muscle were measured, andblood samples as well as vastus lateralis muscle biopsies were collected. Clenbuterolincreased resting energy expenditure by 21% (P P = 0.006), whereas carbohydrate oxidation was unchanged. Phosphorylation ofmTORSer2448 and PKA substrates increased by 121% (P = 0.004) and 35%(P = 0.006), respectively, with clenbuterol. Maximal voluntary contraction torquedecreased by 4% (P = 0.026) and the half-relaxation time shortened by 9%(P = 0.046), while voluntary activation, time to peak twitch, and peak twitch torquedid not change significantly with clenbuterol. Glycogen content of the vastus lateralismuscle did not change with clenbuterol. Clenbuterol increased circulating levels ofglucose (+30%; P P = 0.004), insulin (+130%; P = 0.009), andfatty acids (+180%; P = 0.001). Collectively, these findings indicate that clenbuterol isan efficient thermogenic substance that possibly also exerts muscle hypertrophicactions in humans. For these reasons, the restrictions imposed against clenbuterol incompetitive sports seem warranted.

Item Type: Article
Authors/Creators:Jessen, S and Solheim, SA and Jacobson, GA and Eibye, K and Bangsbo, J and Nordsborg, NB and Hostrup, M
Keywords: beta2-agonist, muscle doping, clenbuterol, anabolic, muscle hypertrophy
Journal or Publication Title: Drug Testing and Analysis
Publisher: John Wiley & Sons
ISSN: 1942-7603
DOI / ID Number: 10.1002/dta.2755
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Copyright 2019 John Wiley & Sons, Ltd.

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