Protein metabolism may be perturbed in
intrauterine growth restriction (IUGR).
Arginine is indispensable for growth and
nitrogen balance in young mammals. Fetuses with IUGR therefore may benefit from
arginine supplementation. The purpose of this study was to determine 1) the effects of IUGR on
protein metabolism in the ovine fetus and 2) the effects of
arginine or mixed
amino acid (AA) infusion on
protein metabolism in these fetuses. Pregnant ewes and their fetuses were catheterized at 110 d gestation and randomly assigned to control or IUGR groups. IUGR was induced by repetitive placental embolization. Parameters of fetal
protein metabolism were determined from [ring-(2)H(5)]
phenylalanine kinetics at baseline and in response to a 4-h infusion of either
arginine or an isonitrogenous AA mixture. There were no differences in
protein metabolism between control and IUGR groups either at baseline or in response to
arginine or AA treatment. Both
arginine and AA infusion increased fetal
protein accretion in both groups.
Arginine did this by decreasing
protein turnover, synthesis, and breakdown. AAs increased
protein turnover and synthesis while decreasing
protein breakdown. AA infusion resulted in a significantly higher increase in
protein accretion than
arginine infusion. Thus, in the ovine fetus, placental embolization has no clear effect on
protein metabolism.
Arginine and AAs both stimulate
protein accretion but do so in distinctly different ways. Mixed AA infusion has a greater effect on
protein accretion than
arginine alone and therefore may be a better strategy for stimulating fetal growth.