S. Tesseraud et al., DIETARY LYSINE DEFICIENCY GREATLY AFFECTS MUSCLE AND LIVER PROTEIN-TURNOVER IN GROWING CHICKENS, British Journal of Nutrition, 75(6), 1996, pp. 853-865
We analysed the respective influences of age and lysine deficiency on
skeletal muscle and Liver protein turnover, Growing male broilers were
fed ad libitum on isoenergetic diets containing 200 g crude protein/k
g which varied in their lysine content (7.7 or 10.1 g/kg). Fractional
rates of protein synthesis (FSR) were measured in vivo in the liver an
d the pectoralis major muscle of 2-, 3- and 4-week-old chickens (flood
ing dose of L-[4-H-3]phenylalanine). Fractional rates of proteolysis (
FBR) were estimated for the same tissues as the difference between syn
thesis and growth, Over the 2-week period Liver FSR and FBR were uncha
nged, whereas muscle FSR decreased with age, This developmental declin
e was related to the lower capacity for protein synthesis (Cs) without
any modifications of the translational efficiency, Whatever the age,
lysine deficiency resulted in significant decreases in body weight, ti
ssue protein content and tissue protein deposition, apparently because
of reduced amounts of proteins synthesized, We recorded a difference
in the response of the two tissues to lysine deficiency, the pectorali
s major being more sensitive than the liver. When comparing birds of t
he same age, Liver FSR and FBR were not modified by the diet, whereas
muscle FSR, Cs and FBR were higher in chicks fed on a lysine-deficient
diet than in the controls, Conversely, when chicks of similar weights
were compared, the main effect of the dietary deficiency was an incre
ase in muscle FBR. The results suggest that lysine deficiency not only
delayed chick development so that protein turnover was affected, but
also induced greater changes in metabolism, Thus, the principal mechan
ism whereby muscle mass decreased appeared to be a change in FBR.