Permeability of the human placenta in vivo to four non-metabolized hydrophilic molecules.

Abstract
Permeability of the human placenta to four permeants of different molecular size was measured at Caesarean section in seven normal full-term pregnancies. Placental clearance for mannitol was 8.7 .+-. 1.1 ml min-1 (mean .+-. S.E.M.), lactulose 6.3 .+-. 0.8, chromium ethylenediaminetetraacetic acid (CrEDTA) 3.7 .+-. 0.5, and inulin 0.98 .+-. 0.1. The permeability data were analysed in terms of restricted diffusion through ''notional'' water-filled pores and found to be incompatible with a single population of uniform pores.