ALTERATIONS IN PROTEIN ACCRETION AND HISTOCHEMICAL-CHARACTERISTICS OF THE M LONGISSIMUS DORSI IN PIGS CAUSED BY SALBUTAMOL (A BETA-ADRENERGIC AGONIST)

Dietary inclusion of the β-agonist, Salbutamol (3.3 ppm), to growing pigs (50-90 kg body weight, 44 days of treatment) significantly increased the weight of the longissimus dorsi muscle (17%). Histochemical identification of muscle sections from m. longissimus dorsi into slow-twitch (ST) and fast-twitch (FTa and FTb) fibres showed that Salbutamol significantly reduced the relative distribution of FTa fibres in both area and number, whereas the relative distribution in numbers of FTb fibres increased, indicating a conversion of FTa to FTb fibres. Results from the calculated volume contribution of each fibre type (weight of longissimus muscle x relative area of fibre type) indicate that the increased protein accretion in m. longissimus dorsi caused by Salbutamol was mainly associated with hypertrophy in FTb fibres or in histochemically identified non-oxidative fibres. The combined changes in protein accretion and fibre type distribution caused by Salbutamol may however result in a lower aerobic capacity of skeletal muscles. © 1990, Taylor & Francis Group, LLC. All rights reserved.