Distribution of blood–muscle for clenbuterol in rat using microdialysis

Clenbuterol is clinically used as a bronchodilator, but it is also illegally used to increase lean meat in animal husbandry. To investigate the muscle distribution of protein-unbound clenbuterol, a microdialysis technique coupled to liquid chromatography system was applied to simultaneously monitor clenbuterol in rat blood and muscle. Two microdialysis probes were implanted into the jugular vein/right atrium and hind leg muscle of rat for sampling after clenbuterol administration (10 mg/kg) through the femoral vein. Dialysate samples of clenbuterol were separated by a reversed-phase column (250 mm × 4 mm I.D., particle size 5 μm). The results indicate that the maximum concentration of clenbuterol in muscle was found at 30–45 min after clenbuterol administration (10 mg/kg) and the area under concentration curve (AUC) of clenbuterol in blood and in muscle were 942.75 ± 101.92 and 174.81 ± 13.03 min μg/mL, respectively. The AUCmuscle/AUCblood was 0.20 ± 0.03 representing about 20% of the clenbuterol distributing into the muscle. The elimination half-life of clenbuterol in the blood and muscle were about 2 and 6 h, respectively. These results suggest that the protein-unbound concentration of clenbuterol sustained a high level and prolonged elimination in the muscle. The accumulation of clenbuterol might result in some clinical effects when clenbuterol-contaminated meat was consumed.