Transport kinetics of alpha-aminoisobutyric acid in the perfused human placental lobule in vitro

ABSTRACT

The transports kinetics of -aminoisobutyric acid [AIB] has been investigated in the human placenta in vitro using perfusion of isolated placental lobules. NCTC 135 tissue culture medium diluted with Earle's salt solution was used as the perfusate, and tritiated water was used as the reference marker. The transport fraction of AIB averaged 13.2% of that of tritiated water in 5 single-bolus injection experiments. The differential transport rates for 10, 25, 50, 75 and 90% cumulative efflux in the fetal vein of the study and the reference substances differed significantly as well. The transport kinetic parameters as area under the curve, clearance, elimination constant, time for maximum response, absorption rate and elimination rate of the amino acid averaged 0.12, 19.8, 0.78, 1.28, 0.10 and 0.06 times, respectively. Plotting of relative AIB transport ratios as a function of perfusion time demonstrated the active nature of amino acid transport in our perfusion conditions. Conclusions: The transport and kinetic parameters employed in the study may be useful in assessing dynamic placental membrane function of A type amino acids and other substances in varying experimental conditions as well as in disease states