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Effects of Cimaterol on Rabbit Growth and Myofibrillar Protein Degradation and on Calcium-Dependent Proteinase and Calpastatin Activities in Skeletal Muscle^1,2,3,

Oregon State University, Corvallis 97331-6702

Abstract

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-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.

¹ Published as paper number 8738 of the Oregon Agric. Exp. Sta.

² The authors acknowledge the generous assistance of M. Koohmaraie in development of assays for calcium-dependent proteinases and calpastatin. The authors also thank Helen Chesbrough for typing the manuscript. Cimaterol was a gift of American Cyanamid Co., Princeton, NJ.

³ Supported in part by USDA grant 88-37265-3796.

⁴ Dept. of Anim. Sci., Oregon State Univ.

⁵ Faculty of Agric., Sana'a Univ., Sana'a, Yemen Arab Republic.

⁶ Reprint requests.

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