Proline is synthesized from intravenously infused arginine by piglets consuming low proline diets

Abstract

Arginine (ARG) may be a significant precursor for proline (PRO) synthesis; therefore in vivo ARG kinetics were studied. Eighteen intact, male, Yorkshire piglets, 2–4 d of age, underwent surgery to install catheters into the jugular vein for blood sampling, the stomach for feeding and the femoral vein for isotope infusion. Piglets were randomly assigned to either a low ARG (–ARG), a low PRO (–PRO) or a control (CON) diet. After 7 d, there was no difference between diets in average daily gain, feed to gain ratio, or in the concentration of protein, fat or ash in the piglet bodies on a dry matter basis. A primed constant infusion of U-14C-ARG (prime = 278 kBq kg−1; constant = 370 kBq kg−1 h−1) was performed for 4 h with blood and breath samples taken at 30-min intervals. There were no significant differences among diets in the amount of 14C-ARG oxidized to 14C-CO2. ARG flux was not significantly different among diets (–ARG = 306.2; –PRO = 584.5; CON = 407.61 μmol kg−1 h−1). Diet affected the fractional rate of conversion of ARG to citrulline (–ARG = 4.7; –PRO = 87.2; CON = 23.1 μmol kg−1 h−1, P = 0.07) and PRO (–ARG = 0.8; –PRO = 56.6; CON = 2.9 μmol kg−1 h−1, P = 0.1). Differences in fractional rate of conversion of labelled ARG to ornithine (–ARG = 14.5; –PRO = 69.3; CON = 19.2 μmol kg−1 h−1) or glutamate (–ARG = 13.3; –PRO = 5.3; CON = 6.5 μmol kg−1 h−1) were not significant. The conversion of ARG to PRO has not previously been reported in vivo in the neonatal piglet. These data indicate that intravenously supplied ARG is a significant precursor for endogenous PRO synthesis in the neonatal piglet. Key words: Arginine, proline, swine, amino acids, urea cycle, requirement