Fetal supply of amino acids and amino nitrogen after maternal infusion of amino acids in pregnant sheep

OBJECTIVE: The objective of the study was to determine whether a prolonged maternal infusion of amino acids would increase the umbilical uptake of amino acids and uteroplacental ammonia production. STUDY DESIGN: Six pregnant sheep (134.5 +/- 2.3 days after conception) were infused for 12 hours overnight with an amino acid solution. Uterine and umbilical blood flows were measured with the ethanol steady-state diffusion technique before (control) and during (experimental) infusion. Plasma amino acid and whole-blood ammonia concentrations were measured. RESULTS: After infusion, despite an increase in maternal arterial amino acid concentration, umbilical uptakes increased significantly only for branched-chain amino acids. Fetal ammonia concentrations and uteroplacental ammonia production increased moderately. Fetal nitrogen supply did not increase. Uterine nitrogen uptake represented 36% of the maternal nitrogen intake in the control period and 14% in the experimental period. CONCLUSION: Prolonged maternal infusion of an amino acid solution was a relatively ineffective method of increasing fetal amino acid supply.