ABSORPTION AND SECRETION OF EXOGENOUS AND ENDOGENOUS N ALONG THE DIGESTIVE-TRACT AND KINETIC-PARAMETERS OF PROTEIN-METABOLISM IN GROWING PIGS .2. DETERMINING KINETIC-PARAMETERS OF PROTEIN-METABOLISM IN THE PIGUSING THE N-15 TRACER TECHNIQUE

Three pigs of about 30 kg body weight were given a wheat-bone meal die t (intake: 1200 g DM/day, 218 g protein/day). One of them was labelled by continuous infusion of L-[N-15]leucine into the vena jugularis (in fusion rate: 15.16 m mole N-15 excess/day) over the whole experimental time of 8 days. During the 5-day preperiod and the following 3-day ex perimental period, samples of urine collected though the bladder cathe ter were taken at intervals of 2 h at the beginning and then every 12 h and analysed for N and N-15. Using these tracer data and the N balan ce data, the kinetic parameters of protein metabolism (protein synthes is, breakdown, pool sizes, half lives) were computed with the help of the end-product method and the 3-compartment model, as described by SP RINSON and RITTENBERG (1949). From the results, which correspond to th ose of other authors estimated by different methods, it can be conclud ed that the method using [N-15]leucine as tracer is suitable for deter mining the synthesis and breakdown rates of whole-body protein, if leu cine in food is neither a limiting nor surplus amino acid.