Effect of food intake on hind-limb and whole-body protein metabolism in young growing sheep: chronic studies based on arterio-venous techniques

Abstract

~ ~~~Whole-body protein synthesis, estimated by the irreversible loss rate procedure, and hind-leg protein metabolism determined by arterio-venous techniques were monitored in response to three nutritional conditions (approximately 0.6, 1 2 and 1.8 x energy maintenance (M)) in ten wether lambs (33 kg average live weight). In all lambs and treatments measurements were based on radiolabelled phenylalanine, but the terminal procedures (five a t 0.6 x M and five at 1.8 x M) also included infusion of[ I-'3Clleucine ; this permitted comparison of amino acids catabolized (leucine) and non-metabolized (phenylalanine) by the hind-limb tissues. Whole-body protein synthesis increased with intake and the relationship with energy expenditure was slightly lower than that reported previously for pigs and cattle. The efficiency of protein retention: protein synthesis did not exceed 0.25 between the two intake extremes. Effects of intake on amino acid oxidation were similar to those observed for cattle. Hind-limb protein synthesis also increased significantly (P < 0001) in response to intake. Estimates of protein gain, from net uptake values, indicated that the tissues made a greater proportional contribution to total protein retention above M and to protein loss below M, emphasizing the role played by muscle tissue in providing mobile protein stores. The rates of protein synthesis calculated depended on the selection of precursor (blood) metabolite, but rates based on leucine always exceeded those based on phenylalanine when precursor from the same pool was selected. The incremental efficiency of protein retained: protein synthesis was apparently unity between 0.6 and 1.2 x M but 0.3 from 1.2 to 1.8 x M. Blood flow through the iliac artery was also proportional to intake. Leucine and 0x0-acid catabolism to carbon dioxide increased with intake such that the metabolic fate of the amino acid was distributed in the proportion 2: I between protein gain and oxidation. The rates of oxidation were only 1-3% the reported capacity of the rate-limiting dehydrogenase enzyme in muscle, but sufficient enzyme activity resides in the hindlimb adipose tissue to account for such catabolism. 1987) and, thus, small changes in the balance of the two processes can produce marked effects on net anabolism and production efficiency. One effective modulator of protein turnover is intake and for a variety of commercial species, including pig (Reeds et ul. 1980),

Somatotropin-induced protein anabolism in hindquarters and portal-drained viscera of growing pigs

“…We observed in our study no significant net release of 13 CO 2 by HQ, thus supporting the assumption that oxidation of phenylalanine is negligible by the tissues of the HQ in vivo. This finding is similar to results obtained by Harris et al (27), in that they observed no net release of 14 CO 2 across the HQ and no venous accumulation of p-hydroxy-phenylpyruvate formed during the hydroxylation of phenylalanine to tyrosine. As a result of our observation in this respect, we have assumed that all [1-13 C]phenylalanine taken up by the HQ is incorporated into protein, because the rate of conversion to tyrosine was not quantified.…”

Quantitative aspects of protein fractional synthesis rates in ruminants

“…A set of 25 publications including 624 observations were found in the literature (Buttery et al, 1975;Lobley et al, 1980;Davis et al, 1981;Bryant and Smith, 1982a, b;Sinnett-Smith et al, 1983;Schaefer et al, 1986;Bohorov et al, 1987;Attaix et al, 1988a, b;Early et al, 1988; Abdul-Razzaq and Bickerstaffe, 1989;Eisemann et al, 1989;Champredon et al, 1990;Early et al, 1990;Hunter and Magner, 1990;Lobley et al, 1990;Baracos et al, 1991;Attaix et al, 1992;Harris et al, 1992;Lobley et al, 1992;Southorn et al, 1992;Crompton and Lomax, 1993;Lobley et al, 1994;Tauveron et al, 1994 (France et al, 1988 (Tomassone et al, 1992 (France et al, 1988). However, this compartment has a short half-life of between 2 and 5 s (Martin et al, 1977) .…”

Effect of intake on whole body plasma amino acid kinetics in sheep

“…While intake has been shown to be a potent regulator of such fluxes (e.g. Pell et al [1]; Young et al [2]; Harris et al [3]) there is still controversy as to how different tissues might respond and the effect this has on whole body kinetics. This may be because of the technique and tracer AA used (e.g.…”