Estimation of rate of protein synthesis by constant infusion of labelled amino acids in pigs

Abstract

I. The fractional synthetic rates of tissue proteins were studied in growing pigs using the constant-infusion technique of tracer-labelled amino acids ( [l4C]1eucine and [14C]lysine) and the mathetmatical model for calculation, employed in rats by Garlick, Millward &James (1973).2 . During a 6 h infusion, samples were taken from blood and muscle and at the end of the infusion from liver, muscle, pancreas, heart, duodenum, jejunum, ileum, colon, and skin. The specific radioactivity of free and protein-bound leucine and lysine was estimated. 3. A quasi-steady-state in the specific radioactivity of free plasma leucine and lysine was reached within approximately z h, the rate-constants being 35 and 48/d respectively.4. The specific radioactivity of free leucine and lysine in plasma was used to calculate the flux of these amino acids. It was found to be higher than the daily intake.5. The average fractional rate of protein synthesis in muscle and heart was 8.1 %/d, in small and large intestine the values were 50 and 33 %/d respectively and in liver and pancreas more than Ioo%/d.6. The calculation of protein synthetic rate in pig tissue using the constant-infusion method of labelled amino acids seems to be a suitable tool for study of this species.

Protein synthesis: are there real species differences?

“…The validity of the values which are obtained from the blood free amino acid specific activity may therefore depend as much upon the choice of the amino acid as upon any other factor. It would appear for example that in man and the pig the flux of lysine gives consistently lower estimates of body protein synthesis than does leucine (Simon et al 1978;Motil et al 1979) ( Table 2). This raises the question as to which is the more correct value.…”

Protein synthesis and retention in some tissues of the young pig as influenced by dietary protein intake after early-weaning. Possible connection to the energy metabolism

“…Lower figures (7.6 % per d) were obtained in the gastrocnemius muscle of 20-30 kg pigs (Edmunds, Buttery and Fisher, 1978 ;Simon et al, 1978) or in the leg muscles of 70 kg pigs (Garlick, Burk and Swick, 1976). An important decrease (16.2 to 10.2 %) has been shown recently in rats from 21 to 60 days post-partum .…”

Can amino acid requirements for nutritional maintenance in adult humans be approximated from the amino acid composition of body mixed proteins?

“…Also, while the University of Illinois pattern (UIP) of amino acids required by adult swine (29,30) does not resemble that for mixed proteins in the body, the UIP is based on limited data, and the estimates of requirements show large differences depending upon whether a nitrogen balance equilibrium or a relatively small positive body nitrogen balance of 1 g is used as the criterion for evaluation. Finally, the rate of whole-body protein synthesis (WBPS) in growing pigs approximates 8-15 g kg-'day-' (31)(32)(33), in comparison with that in adult humans of about 4 g kg-'day-'; when protein and energy intakes are at about maintenance levels in young pigs the rates of WBPS are substantially below those achieved when the ration supplies twice and three times the maintenance requirement (34) or adequate levels of protein (35). In contrast, according to Pacy et at (36), in adult human subjects there is relatively little effect on whole-body protein turnover with changes in protein intake, during 2-week periods, over a wide range covering submaintenance and supramaintenance levels.…”