EFFECTS OF THE BETA-ADRENERGIC AGONIST SALBUTAMOL AND ITS WITHDRAWAL ON PROTEIN-METABOLISM OF LAMBS

Rasa Aragonesa lambs were used to evaluate the repartitioning effects of a beta-adrenergic agonist and its withdrawal on nutrient metabolism . One group of animals (T-I) was fed salbutamol at a dose of 2 mg x kg (-1) diet x day(-1) for 38 days, while in another group (T-II) the bet a-adrenergic agonist was discontinued in the diet 5 days before slaugh ter on the 43rd day. The semitendinosus muscle protein content increas ed (p < 0.05), while fat and collagen content decreased (p < 0.05) in the T-I group. These differences were not apparent in the group from w hich salbutamol was withdrawn. Muscle protein degradation was diminish ed (p < 0.05) in both treated groups. The serum free fatty acid level was markedly enhanced (p < 0.05) in the T-I group. Total essential ami no acid serum levels were reduced (p < 0.05) after the withdrawal peri od. Ketogenic and urea cycle amino acids were reduced (p < 0.05) in th e salbutamol-fed T-I group and glycogenic amino acids were diminished (p < 0.05) in the T-II experimental group. The data show that salbutam ol is able to increase muscle content at the expense of fat stores in productive animals. However, these repartitioning effects are circumve nted by a 5-day period of withdrawal, in which concomitant metabolic c hanges in lipid and protein turnover and plasma amino acid profiles oc cur.