Transplacental clearances of inert hydrophilic tracers in rabbits of 18 days gestation.
Transplacental clearances were measured for radiolabelled Cl-, SO4(2-), mannitol, sucrose, raffinose, PEG-900 and inulin. Maternal placental blood flows were measured with radiolabelled microspheres. At 18 days of gestation (term 31 days), the fetuses and extra-fetal fluids were growing at 55 and 32 per cent per day, accounting for a net transplacental filtration rate of 14.2 nl/sec per gram placental weight. Pore theory and a least squares fit of the Patlak equation yielded an equivalent pore radius of 1.75 nm. It was demonstrated that the clearance of the largest tracer, inulin, was 30 times higher than it would have been in the absence of net filtration. Comparison with literature data showed that there was a small increase in placental permeability per gram placenta between 14 and 18 days of gestation but that the increase between 18 and 28 days of gestation was about 14-fold for Cl- and 300-fold for inulin. There was no evidence for a decreasing equivalent pore radius in the course of gestation from 14-18 days.
D000818:Animals; D005314:Embryonic and Fetal Development / Q000502:physiology; D005374:Filtration; D005865:Gestational Age; D008657:Metabolic Clearance Rate; D010539:Permeability; D010920:Placenta / Q000378:metabolism*; D011817:Rabbits; D011849:Radioactive Tracers; D012995:Solubility; D013045:Species Specificity; D014867:Water
D011849:Radioactive Tracers; D014867:Water