Growth and muscle protein turnover in the chick

Abstract

The growth rates of young chicks were varied from 0 to 10% per day by manipulation of the adequacy of the amino acid and energy supply. The rates of protein synthesis in the white breast (pectoralis thoracica) muscle and the dark leg (gastrocnemius and peronaeus longus) muscles were estimated by feeding l-[U-(14)C]tyrosine in amino acid/agar-gel diets (;dietary infusion'). This treatment rapidly and consistently produced an isotopic equilibrium in the expired CO(2) and in the free tyrosine of plasma and the muscles. Wholebody protein synthesis in 2-week-old chicks was estimated from the tyrosine flux and was 6.4g/day per 100g body wt. In 1-week-old chicks the rate of protein synthesis was more rapid in the breast muscles than in the leg muscles, but decreased until the rates were similar in 2-week-old birds. Synthesis was also more rapid in fast-growing Rock Cornish broilers than in medium-slow-growing New HampshirexSingle Comb White Leghorn chicks. No or barely significant decrease in the high rates of protein synthesis, in the protein/RNA ratio and in the activity of RNA for protein synthesis occurred in non- or slow-growing chicks fed on diets deficient in lysine, total nitrogen or energy. Thus the machinery of protein synthesis in the young chick seems to be relatively insensitive to dietary manipulation. In the leg muscles, there was a small but significant correlation between the fractional rate of growth and protein synthesis. A decrease in the fractional rate of degradation, however, appeared to account for much of the accumulation of muscle protein in rapidly growing birds. In addition, the rapid accumulation of breast-muscle protein in rapidly growing chicks appeared to be achieved almost entirely by a marked decrease in the fractional rate of degradation.

Protein turnover of breast muscle in germ-free and conventional chicks

“…Harney et al (1976) and Maruyama et al (1978) reported that dietary infusion of labelled amino acid produced isotope equilibrium in plasma and muscle, as evidenced by a plateau in the radioactivity of the expired CO,, within 6 h. After following a similar dietary infusion procedure for a longer period of 8 h, the proportion of phenylalanine oxidized, as shown in Fig. 1, was considerably reduced on feeding the N F diet, suggesting that there was an adaptation of birds to protein depletion in order to save N loss, as found in rats (McFarlane & von Holt, 1969;Reeds, 1974) and implied by studies in rats and chicks on changes in activities of enzymes involved in amino acid catabolism (Schimke, 1962;Scholz & Featherston, 1969).…”

“…Protein turnover was measured by two methods, a dietary-infusion method (Maruyama et al 1978) and a large-dose injection method (Garlick et al 1980).…”

Meat tenderness and muscle growth: is there any relationship?

“…Of all the possible mechanisms of increasing muscle deposition, only the mechanism that involves suppression of protein degradation will result in decreased meat tenderness. Unfortunately, suppression of protein degradation seems to be the mechanism that is responsible for differences in the rates of muscle growth in domestic animals (Bohorov, Buttery, Correia, & Soar, 1987;Koohmaraie, Killefer, et al, 1995;Maruyama, Sunde, & Swick, 1978;Reeds, Hay, Dorwood, & Palmer, 1986). The best examples in support of the negative effects of the suppression of myofibrillar protein degradation on meat tenderness are two welldocumented cases.…”

Effect of dietary lysine on muscle protein turnover in growing chickens

“…Des poulets mâles à croissance rapide sont nourris ad libitum jusqu'à lâge de 3 semaines avec des régimes isoénergétiques titrant 20% de protéines totales mais différant par leur teneur en lysine (6,(5)(6)(7)(8)(9)(10)(11)3 glkg). Les (Waterlow, 1984;Arnal et al, 1987 (Maruyama et al, 1978). Other studies were performed in order to determine the effect of a limiting amino acid supplementation in protein-starved chicks.…”