The objectives of this study were to examine effects of a
beta-adrenergic agonist (
cimaterol) on growth and muscle development in rabbits and to examine
cimaterol's effects on myofibrillar protein degradation (MPD) and on activities of several
proteolytic enzymes including the
calcium-dependent
proteinases (
CDP). Twelve New Zealand White rabbits were assigned to either control diets or to diets containing
cimaterol for 35 d, after which they were killed and effects on performance and tissue
weight gains were determined. Urine was collected from d 21 through 28 from each rabbit for assessment of
N tau-methylhistidine (NMH) excretion.
Cimaterol increased rates of gain, efficiency of gain and skeletal muscle weights. Enhancement in muscle weight was associated with an increase in total
DNA and with a reduction in NMH.
Cimaterol did not affect activities of
cathepsin B,
cathepsin D or neutral
serine proteinase, but it reduced activities of the millimolar and micromolar forms of the
CDP by 58 and 57%, respectively, and it reduced activity of the inhibitor of the
CDP (
calpastatin) by 52%.
Cimaterol-dependent myofibrillar
protein accretion was likely mediated, at least in part, by a reduction in MPD. The change in MPD was associated with a reduction in muscle
CDP activities.
Cimaterol-dependent muscle
hypertrophy therefore may involve changes in
calcium-dependent proteolysis of myofibrillar
proteins. The significance of the effects of
cimaterol on
calpastatin activity is not known.