Hind-limb protein metabolism in growing sheep; effects of acute and chronic infusion of clenbuterol by close arterial and systemic routes

1. Close arterial infusion of clenbuterol (0.7 μg/hr) for a 3 hr period led to decreased protein synthesis and degradation (both P < 0.05) across the hind-limb of sheep. 2. Systemic infusion of the drug (14 μg/hr) for a similar period increased blood flow (P < 0.001) through the hind-limb and decreased protein degradation (P < 0.05). 3. Following chronic (7 day) close-arterial infusion of clenbuterol (1.9 μg/hr) hind-limb protein synthesis and degradation again declined (P < 0.05) but this was apparently not recovered during 7 days of drug withdrawal. 4. In consequence, during subsequent systemic infusion of the drug (62 μg/hr) the lower rates of protein metabolism were not altered significantly, despite improved whole nitrogen retention (+ 30%, P < 0.01). 5. The results are discussed with reference to the differential actions of β-agonists on the various tissues of the hind-limb.