Assessment of D-glucose transport kinetics in the perfused human placenta: an in vitro study

There have been no reports to date on glucose transport kinetics and the effect of graded hyperglycemia in the human placenta in non-steady-state conditions.

The transport kinetics of D-glucose in the human placenta was investigated in non-steady state conditions in vitro using perfusion of isolated placental lobules. National Cancer Tissue Culture (NCTC) 135 culture medium, diluted with Earle's buffered salt solution was used as the perfusate. 14C-Labeled D-glucose and water as reference were injected as a single bolus into the maternal arterial perfusate. Perfusate samples were collected and analyzed from the maternal and fetal venous outflows.

In four successful perfusions, differential transport rates of glucose in the maternal-fetal direction averaged 1.03, 1.02, 1.09, 1.04 and 1.03 times those of corresponding tritiated water transport rates for 10, 25, 50, 75 and 90% of efflux fractions, respectively. Glucose transport fraction, expressed as percentage of injected maternal dose averaged 84 +/- 3.1% of water transport fraction in the four perfusions. Glucose kinetic parameters expressed as area under the curve, elimination constant (Kel), clearance, time for maximum response, absorption rate and elimination rate averaged 0.25, 0.29, 3.96, 1.02, 0.25 and 0.18 times that of the corresponding tritiated water value, respectively. Neither the different kinetic parameters nor the transport fraction indices differed significantly when glucose concentrations in the same perfusions were raised successively from 5.56 to 27.80 and then to 55.6 mmol/L.

We speculate that within physiological limits, hyperglycemia per se plays no significant part in altering glucose transport kinetics across the human placenta in the maternal-fetal direction.