Effect of insulin on transport kinetics of alpha-aminoisobutyric acid in the perfused human placental lobule in vitro.

BACKGROUND The limited data available on the role of insulin on maternal-fetal transport of amino acids prompted us to undertake this study. METHODS Transport kinetics of a model amino acid, alpha-aminoisobutyric acid (AIB) was investigated in perfusion of isolated human placental lobules in vitro in non steady-state conditions and the effect of therapeutic dose of insulin was assessed in parallel series of perfusions. National Culture and Tissue Collection medium diluted with Earle's buffered salt solution was used as the perfusate and tritiated water was used as the reference marker for comparison. RESULTS In five successful perfusions with insulin, differential transport rate indices of AIB for 10, 25, 50, 75 and 90% of efflux fractions in the fetal venous outflow averaged 0.76, 1.03, 1.02, 1.09, 1.04 and 1.03 times those of reference values, respectively. The indices differed significantly than in controls for 10, 25 and 50% efflux fractions, but not in the case of 75 and 90% efflux values. The AIB transport fraction (TF), expressed as percentage of injected maternal dose, averaged 29.4 +/- 5.4% and 38.7 +/- 6.2% of the corresponding reference marker value in control and insulin series, respectively. With regards to the pharmacokinetic transport parameters, the absorption and elimination rates of the amino acid were significantly higher in the study group than in the control. CONCLUSION We conclude that insulin, in physiological and therapeutic doses, stimulates maternal-fetal AIB transport in vitro, in the perfused human placental lobule.