Abstract
β2-agonist, clenbuterol (CLE) is used as a non-steroidal anabolic drug in sports doping and selectively binds to β2 adrenoceptor (AR). Although many studies have been reported on post-translational modification of β2 AR in muscles of CLE-administered animals, little is known about transcriptional control of them. Therefore, the effects of CLE-administration (dose = 1.0 mg/kg BW/day, sc) for 10 days on the mRNA expression of β ARs (β1, β2 and β3 ARs) in the fast-twitch extensor digitorum longus (EDL), the slow-twitch soleus (SOL), mixed-type gastrocnemius (GAS) and left ventricle (LV) muscles were studied in rats. Adult male Sprague Dawley rats were randomly divided into CLE-administered and control (CON) groups. The expression of β ARs was analyzed by real-time RT-PCR. EDL and GAS weights in CLE group were significantly higher than those in CON group. However, SOL and LV weights were not significantly different between both groups. The β2 AR mRNA levels of EDL and LV in CLE group were significantly lower than those in CON group. The β1 AR mRNA level of LV in CLE group was also significantly lower than that in CON group. From these results, CLE induced down-regulation of β1 and β2 ARs in LV without hypertrophy and down-regulation of β2 AR in hypertrophied EDL, suggesting that the effects of CLE on the mRNA expression of β ARs and muscle hypertrophy are dependent upon each muscle type. [J Physiol Sci. 2008;58 Suppl:S69]
