Flow-dependent transfer of antipyrine in the human placenta in vitro.

Placental transfer of antipyrine, a small liposoluble molecule, was investigated at varying flow rates using dual perfusion of human placental lobules. With a flow ratio equal to unity, the foetal transport fraction (foetal vein concentration X 100/maternal artery concentration) of antipyrine averaged 0.33. It has been suggested that effectiveness of exchange in the lobule perfused in vitro approximated that of a concurrent model with an antipyrine 'd' coefficient between 0.6 and 1.2, including shunting which diverted 16 p. 100 of foetal and 13 p. 100 of maternal flow rates from the exchange area. These observations have been discussed in relation to data obtained in other mammalian placentas and in man in vivo.