Anabolic effects of a non‐myotoxic dose of the β₂‐adrenergic receptor agonist clenbuterol on rat plantaris muscle

Abstract

Previous investigations of the effects of clenbuterol have used suprapharmacological doses that induce myocyte death, alter muscle phenotype and do not approximate the proposed therapeutic dose for humans. Recently we reported that smaller doses of clenbuterol induce muscle growth without causing myocyte death. Here, we have used histochemical and proteomic techniques to investigate the molecular effects of this dose. Male Wistar rats (n = 6, per group) were infused with saline or 10 μg.kg -1 .d -1 clenbuterol via subcutaneously implanted osmotic pumps. After 14 days the animals' plantaris muscles were isolated for histochemical and proteomic analyses. Clenbuterol-induced significant muscle growth with concomitant protein accretion and preferential hypertrophy of fast oxidative glycolytic fibers. Clenbuterol reduced the optical density of mitochondrial staining in fast fibers by 20 % and the glycogen content of the muscle by 30 %. Differential analysis of two-dimensional gels showed that heat shock protein 72 and β-enolase were increased whereas aldolase A, phosphogylcerate mutase, and adenylate kinase decreased. Only heat shock protein 72 has previously been investigated in clenbuterol-treated muscles. In conclusion, the clenbutero linduced increase in muscle growth wass concomitant with qualitative changes in the muscle's proteome that need to be considered when proposing therapeutic uses for this agent.

Enhanced efficacy of enzyme replacement therapy in Pompe disease through mannose-6-phosphate receptor expression in skeletal muscle

“…Caution has been urged due to the relatively high dosages used to achieve muscle hypertrophy in rodent models, and this study used approximately 210 μg/kg/day, given an estimated water consumption for mice of 7 ml/day. However, infusion of a low amount of clenbuterol (only10 μg/kg/day) induced hypertrophy of type II fast, oxidative glycolytic myofibers in rats [25]. Dosing as low as 5 μg/kg/day increased muscle force generation in horses, indicating that much lower doses might be effective [26].…”

On the Rate of Synthesis of Individual Proteins within and between Different Striated Muscles of the Rat

“…The diversity of muscle phenotypes is largely due to differential expression of different isoforms of key contractile proteins, which concomitantly dictates the relative abundance of enzymes involved in substrate utilisation and energy production. In the past, we have reported the relative abundance of proteins in various rat striated muscles using proteomic techniques including 2DGE and MALDI-TOF MS e.g., [17,18,19] but there is currently a lack of equivalent data regarding synthesis rates of rat muscle proteins. In particular, we sought to investigate whether the rank order of synthesis rates for a selection of proteins is similar across different striated muscles or if enzymes that exist at a greater concentration in a particular muscle also exhibit a more rapid rate of renewal.…”

Effects of clenbuterol therapy on mitochondrial activity in skeletal musculature of RAO affected horses

“…In rats, 14 days of clenbuterol treatment led to increased muscle mass and protein content. In fast muscle fibers the optic density of mitochondria was reduced by 20% and the glycogen content was reduced by 30 % in comparison to controls (Burniston et al 2007). …”