Whole-body protein synthesis in growing barrows: diurnal and day-to-day variation and the effect of site of tracer infusion and sampling

Abstract

In the first experiment, two catheters were placed in one of three sites for infusion and sampling (vena cava and vena cava with 7 cm between catheter tips, VC/VC, n = 5; right ventricle and atrium, RV/RA, n = 5; anterior aorta and left ventricle, AA/LV, n = 4) to determine the effect of site on the measurement of CO2 and leucine kinetics. Pigs received a 6-h continuous i.v. infusion of NaH13CO3 (1.45 µmol h−1 kg−1, preceded by a priming dose of 2.05 µmol kg−1) and of L[1-13C]leucine (9.7 µmol h−1 kg−1, preceded by a priming dose of 9.7 µmol kg−1), the following day. No effect (P > 0.10) of site was observed on NaH13CO3 recovery rate, leucine irreversible loss rate (leucine ILR) and leucine used for protein synthesis (LS). A tendency (P < 0.10) for increased leucine oxidation (LO) was observed with the VC/VC compared to the RV/RA sites. In the second experiment, six growing barrows with catheters in the VC/VC site were infused as earlier with NaH13CO3 and L[1-13C]leucine for three different 6h periods (12:00 to 18:00 h, first day; 20:00 to 02:00 h, night; 12:00 to 18:00 h, second day) to determine the diurnal and day-to-day variation of CO2 and leucine kinetics. No effect (P > 0.10) of period was observed on NaH13CO3 recovery rate, leucine ILR and LS. The LO was lower (P < 0.05) on the second day compared with the first day (day-to-day variation) while similar (P > 0.10) LO was observed between the first day and night (diurnal variation). Together, these results indicate that 1) the VC/VC site can be used for L[1-13C]leucine and NaH13CO3 infusions, 2) NaH13CO3 recovery studies can be performed either the day preceding or following the measurement of substrate and 3) protein synthesis estimated from a 6-h infusion period can be extrapolated to the 24 h periods under conditions of frequent feeding. Key words: Pigs, leucine, protein synthesis, tracer techniques, diurnal variation