RESUMO
Administration of beta-adrenergic agonists to domestic species can lead to skeletal muscle hypertrophy, probably by reducing the rate of myofibrillar protein breakdown. Myofibrillar breakdown is associated with the calcium-dependent proteinase system (calpains I,II and calpastatin) whose activity also changes during beta-agonist treatment. A number of growth trials using the agonists cimaterol and clenbuterol with cattle, sheep, chicken and rat are reported which suggest a general mechanism whereby beta-agonists reduce calpain I activity, but increase calpain II and calpastatin activity in skeletal muscle. Parallel changes in specific mRNAs indicate that changes in gene expression or stabilisation of mRNA could in part explain the changes in activity.
Assuntos
Agonistas Adrenérgicos beta/farmacologia , Proteínas de Ligação ao Cálcio/genética , Calpaína/genética , Expressão Gênica/efeitos dos fármacos , Músculos/enzimologia , Animais , Bovinos , Galinhas , Etanolaminas/farmacologia , Feminino , Masculino , Músculos/efeitos dos fármacos , RNA Mensageiro/metabolismo , Ratos , Ratos Endogâmicos , OvinosRESUMO
Tissue composition and skeletal muscle cathepsin D (EC 3.4.23.5) activity were measured in wether lambs treated with trenbolone acetate (TBA) and oestradiol-17 beta (Oe) in combination and female lambs treated with TBA or zeranol. Muscle and liver protein fractional synthesis rates and plasma leucine flux were measured in the female lambs. Male castrate lambs treated with TBA plus Oe showed increased growth rate, improved food conversion efficiency, decreased muscle RNA concentration and decreased total cathepsin D activity in muscle. Female lambs treated with TBA or zeranol showed increased weight gain, improved food conversion efficiency, decreased muscle RNA and DNA concentrations and decreased free cathepsin D activity in muscle. Mixed muscle protein fractional synthesis rate was decreased after TBA treatment. Plasma leucine flux, not corrected for oxidation or food intake, was not increased by TBA or zeranol treatment. Treatment of female lambs with TBA or zeranol caused increased growth rate. This increased growth rate is probably due in part to decreased muscle protein degradation, since evidence was obtained that muscle protein synthesis is decreased by TBA and zeranol treatment.