EFFECTS OF SALBUTAMOL, A BETA-2-ADRENERGIC AGONIST, ON MUSCLES OF GROWING PIGS FED DIFFERENT LEVELS OF DIETARY-PROTEIN .2. AEROBIC AND GLYCOLYTIC CAPACITIES AND GLYCOGEN-METABOLISM OF THE LONGISSIMUS-DORSI MUSCLE

Dietary inclusion of salbutamol (3 ppm), a beta2-adrenergic agonist, t o growing pigs from 25 to 90 kg body weight reduced the activities of citrate synthetase (CS) (P<0.01) and 3-OH-acyl-CoA-dehydrogenase (HAD) (P<0.07) by 10 and 8%, respectively, measured on needle biopsies obta ined from the fast-twitch-glycolytic longissimus dorsi muscle at 25, 4 5, 60 and 90 kg body weight. These reductions by salbutamol were induc ed at 60 kg body weight and remained unchanged. On the other hand, sal butamol did not affect the activities of lactate dehydrogenase (LDH), total glycogen synthetase (GS), the glucose-6-phosphate independent fo rm of GS, and muscle glycogen content. The activity of LDH increased b y 41% from 25 to 90 kg body weight (P<0.001), with the steepest increa se from 25 to 45 kg body weight, while the activities of CS and HAD de creased by 25 (P<0.001) and 19% (P<0.001) in control animals, respecti vely. The total GS activity was decreased at 60 and 90 kg body weight by 24% (P<0.01), whereas the independent form of GS did not change in the body weight range examined. The glycogen content was reduced by 20 % (P<0.05) at 90 kg body weight compared to the other body weights. Th ese results indicate that salbutamol treatment decreases muscle oxidat ive capacity. In addition, a marked shift in the metabolic profile tow ards a higher glycolytic and a lower oxidative capacity occurs in the longissimus dorsi muscle during growth in pigs.