Contribution of branched-chain amino acids to uteroplacental ammonia production in sheep

The uteroplacental tissues are a principal site of ammonia production for t he conceptus. The goal of this study was to examine the effect of the compo sition of maternal amino acid (AA) infusate on uteroplacental ammonia produ ction. Seven pregnant ewes (126 +/- 1.4 days gestation) were infused throug h the maternal femoral vein (duration 3.5 h, rate 240 mi per hour) with thr ee solutions of AAs. The first infusate was comparable to commercial parent eral nutrition preparations, the second infusate contained the same solutio n without branched-chain AAs (BCAAs), and the third infusate contained only BCAAs. Blood samples were simultaneously collected from the maternal arter y, uterine vein, fetal artery, and umbilical vein to determine plasma AA co ncentrations and whole blood ammonia concentrations, before (control) and 2 h after (experimental) the start of infusion. Uterine and umbilical blood flows were measured using the ethanol steady-state diffusion method. Result s showed that fetal arterial and venous ammonia concentrations increased si gnificantly after infusions with all AAs or only BCAAs, but not without BCA As. Uteroplacental ammonia production increased in response to each of the three infusates. However, this increase was much greater when the BCAAs wer e present in infusates, We conclude that there is a significant contributio n of BCAAs to the uteroplacental ammonia production. Maternal AA infusions containing BCAAs can result in increased fetal blood ammonia concentrations .