Note on the permeability of the placenta in the rabbit

Abstract

The observations of various anatomists have shown very clearly that there are wide variations in the structure of the placental barrier in such species as the ungulate, the carnivora the rodentia, the chiroptera, and primates. Grosser 1 classifies the placentalia in terms of the layers of tissue which separate the maternal from the fetal blood-streams; but it must also be noted that the same layer of tissue may be of very different morphology in different species. In view of these differences it seems unfortunate that the vast majority of observations which have been made upon the passage of any substance from mother to fetus, or the reverse have been carried out on single species.

Among the few observers who have made comparative experiments on different species are Römer 2 using tetanus antitoxin, and Wislocki 3 using vital dyes. Römer found that the antitoxin passed readily in the human, occasionally in rodents, and never in sheep or cows. Wislocki found that trypan blue passed in small amounts in the rabbit and guinea-pig, but never in the cat and dog. In his discussion he suggests that both his and Romer's results may be dependant upon the varying complexity of the placental barrier in the animals studied.

Experiments have been reported elsewhere 4 in which it was shown that sodium ferrocyanide passed through the placental barrier in the cat from mother to fetus, while iron ammonium citrate was held up by some mechanism located in the fetal ectoderm. Further experiments have demonstrated that in the rabbit both the salts passed from mother to fetus, but it was found that the sodium femocyanide passed the placental barrier somewhat more easily than the iron ammonium citrate; this was shown by the fact that the ferrocyanide appeared in the fetal blood before the citrate, and always remained in greater concentration.