A new method for measuring unidirectional transplacental flux

Measurement of unidirectional transplacental flux: a simplified method

A simple method for determining unidirectional transplacental flux in the in vitro perfusion (transfer factor analysis) has been derived from a general treatment of non-compartmental analysis describing transfer between two accessible pools. This method was validated by comparison of the unidirectional transfer fractions for Evans Blue in a two-pool hydraulic model with the true transfer fractions determined from the pump flow rates in the model. There was excellent agreement between calculated and true transfer fractions. Transfer fractions obtained using this method were also compared to the fractions determined by a previously described technique, deconvolution analysis, for a hydraulic model in which a third, inaccessible pool was interposed between the two accessible pools. Good agreement was found between the two methods. Similar agreement was found for the fractional transfer of [14C]L-lactate in the in vitro perfused human placenta, calculated using transfer factor and deconvolution analysis. The sample collection and data processing are much simpler using the former method but the quality of information obtained is reduced accordingly.

Lactate transfer across the perfused human placenta

The transfer of lactate across the human placenta was investigated using an in vitro dually-perfused placental preparation. Using a novel technique, the unidirectional flux of L-lactate was found to be linearly dependent on L-lactate concentration. In addition, unidirectional transfer rates were found to be the same in both maternal-to-fetal and fetal-to-maternal directions at the same lactate concentration. Transfer of [14C]L-lactate was decreased by approximately 15 per cent in competition with unlabelled L-lactate. Stereospecificity and permeability experiments demonstrated the existence of a transfer mechanism which could distinguish between the L- and D-isomers of lactate. Our data suggest that, while a stereospecific carrier for lactate exists in the perfused placenta, the bulk of transplacental lactate transfer takes place by non-carrier-mediated diffusion.