A comparison of amino acid arteriovenous differences across the liver and placenta of the fetal lamb

Amino acid and ammonia concentrations as well as oxygen content were measured in either the right or left hepatic vein, the umbilical vein, and the umbilical artery in 13 fetal lambs in late gestation. There was an uptake of all of the essential and most of the nonessential amino acids by both lobes of the fetal liver. The umbilical venous-hepatic venous amino acid concentration differences were similar in the two hepatic lobes. While glutamine and glycine were taken up by both hepatic lobes, their metabolically related amino acids, glutamate and serine, were released by the fetal liver into the systemic circulation. There was a reciprocal net placental uptake from the umbilical circulation of glutamate and serine and a net fetal of glutamine and glycine, suggestive of interorgan cycling of these amino acids between the placenta and fetal liver. Total fetal umbilical nitrogen uptake was 0.91 g N.kg-1.day-1. The umbilical venous-hepatic venous differences of ammonia were positive and not significantly different in the two lobes. There was a significant umbilical uptake of ammonia (12.8 +/- 1.8 microM; 0.0078 microM NH3/microM O2). However, 0 the ratios of NH3 to O2 were much higher in each lobe (right, 0.060; left, 0.079; each P less than 0.01) than in the umbilical circulation

The use of electrolyte redox potential to monitor the Ce(IV)/Ce(III) couple

Mathematical modelling of the oxidation reduction redox potential (ORP) of an electrolyte has been carried out for a batch system comprising an electrochemical reactor and an electrolyte circuit containing a redox couple. The ORP can be useful to monitor the environmental impact of chemical species in solution that represent a risk to the environment. Considerations of four fundamental equations, namely, the Nernst equation, a mass balance, Faraday's laws of electrolysis and a first order kinetic equation, leads to an expression for the electrolyte redox potential as a function of the batch time, the electrical charge and the redox concentration. Such an expression facilitates graphical plots which can be used to estimate kinetic parameters, current efficiency and the relative redox concentration. The Ce(IV)/Ce(III) system has been chosen as a model reaction for electrolyte redox potential measurement in a batch recycle system consisting of a pumped flow through a divided FM01-LC parallel plate electrochemical reactor (64 cm2 projected electrode area) and a well mixed tank (3,600 cm3). The differences between experimental and model predictions are discussed

Glycine turnover and oxidation and hepatic serine synthesis from glycine in fetal lambs

[1-13C]- and [1-14C]glycine were infused into chronically catheterized fetal lambs via a branchial vein. At tracer glycine steady state, samples were collected from the fetal abdominal aorta, umbilical vein, and fetal hepatic vein and from the maternal femoral artery and uterine vein. The samples were analyzed for plasma glycine and serine, for glycine and serine 13C atom% excess (APE), and for whole blood 14CO2 and O2 concentrations. Fetal plasma glycine disposal rate (DR) was 12.4 \ub1 0.8 \u3bcmol\ub7min-1\ub7kg fetus-1\ub7CO2 production from decarboxylation of fetal plasma glycine was 1.63 \ub1 0.16 \u3bcmol\ub7min-1\ub7kg fetus-1 and represented 12.3 \ub1 0.7% of DR. Approximately 50% of infused tracer glycine was taken up by the fetal liver with the release of labeled serine and CO2 in the fetal circulation. There was no detectable efflux of tracer glycine from the placenta into the maternal circulation. The tracer production of serine and CO2 accounted for 23 and 17%, respectively, of the hepatic tracer glycine uptake. The labeled CO2 released by the liver was a large fraction (~70%) of the labeled CO2 produced by the fetus. The serine-to-glycine APE ratio in fetal plasma was ~5%. These results indicate that the fetal liver is the major site of fetal plasma glycine decarboxylation and of serine synthesis from plasma glycine