Abstract
It has long been recognized that there are histological changes in the placenta at various stages of pregnancy. There has been little investigation, however, of the possibility that these morphological alterations are linked with coincident changes in the concentration of various metabolites, such as glucose, urea and amino-acids in the blood which bathes the foetal and maternal surfaces of the placental boundary. In recent observations, however, it has been found that the concentration of blood sugar 1 and hemoglobin 2 is strikingly different on the foetal and maternal sides of the placental barrier in the rabbit at the beginning of the last third of the gestation period; on the other hand, at term, the blood sugar and hemoglobin are found to approach much more nearly an equal concentration in the foetal and maternal blood. It is obvious that data derived from observations at term may fail to give a complete understanding of the regulatory activity of the placenta. If the previous observations in the human are viewed in this light, as for instance, the careful description by Plass 3 of the concentration of urea, amino-acids, and total nonprotein nitrogen in foetal and maternal blood at parturition, and the studies of Slemons, 4 it is evident that the data are limited to observations at a single stage of pregnancy.
In the present experiments, a series of 24 rabbits has been observed at various stages of pregnancy from the 26th day until near term, i. e.y the 32nd day. As summarized in the table, it has been found that the urea nitrogen is present in about equal concentration in the foetal and maternal blood; on the contrary, the amino-acid nitrogen and the total non-protein nitrogen are found consistently in greater concentration in foetal than in maternal blood.
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