Effect of dietary lysine on muscle protein turnover in growing chickens

Abstract

― Day-old male chickens were fed ad libitum isoenergetic diets containing 20% crude protein but differing in their lysine content (from 6.5 up to 11.3 g/kg). At 3 weeks of age, protein frac- tional synthesis rates in the pectoralis major muscle were determined using a large dose injection of 120 umol per kg body weight of L -[4-3 H] phenylalanine. Protein gain in the pectoralis major was measured between 19 and 23 days of age. Protein breakdown was obtained by calculating the dif- ference between protein synthesis and deposition. Weight gain varied curvilinearly with dietary ly- sine intake and was maximum for 11.3 g lysine/kg of diet. In birds fed an adequate lysine intake (10.1-11.3 g/kg) protein fractional synthesis and breakdown rates were 23.6-25.9 and 17.8-19.8%/d respectively. Increasing lysine supplementation in the diet resulted in an impairment of protein frac- tional breakdown rates. By contrast, protein fractional synthesis rates remained unchanged owing mainly to an improvement in the synthesis efficiency (kRNA), until birds were fed an adequate lysine intake. These data suggest that the growth rate reduction of chickens fed lysine deficient diets was due to alterations in both rates of protein synthesis and breakdown in skeletal muscle. A maximum protein deposition is achieved when kRNA was optimal, ie for a dietary lysine content of about 9 g/kg, a value close to the requirement. lysine / protein synthesis / protein breakdown / chicken Rsum ― Influence de la lysine alimentaire sur le renouvellement des protines du muscle chez le poulet de chair. Des poulets mles croissance rapide sont nourris ad libitum jusqu' lge de 3 semaines avec des rgimes isonergtiques titrant 20% de protines totales mais diffrant par leur teneur en lysine (6,5-11,3 glkg). Les vitesses de synthse des protines du muscle pectoralis major sont dtermines en utilisant la mthode de surcharge en phnylalanine tritie (injection intra- veineuse de 120,umollkg de poids vif de !-(4-3HJPhe). Le gain protique du muscle pectoralis major est mesur entre les 19 e et 23 6 jours. La dgradation des protines est obtenue par diffrence entre la vitesse de synthse et la vitesse de dpt protique. Le gain de poids varie de faon curv'//r)a/re avec le taux de lysine du rgime alimentaire et atteint un maximum pour un apport de lysine de 11,3 glkg de rgime. Chez les animaux nourris avec un ali- ment quilibr titrant entre 10,1 et 11,3 g de lysinelkg, les vitesses de synthse et de dgradation des protines sont respectivement 23,6-25,9 et ?7,!-!,a%/). La supplmentation en lysine du r- gime entrane une diminution des vitesses de dgradation des protines. En revanche, les vitesses de synthse ne sont pas modifies pour des apports alimentaires de lysine infrieurs au besoin en raison d'une amlioration de l'efficacit de synthse (kRNA). ) .