THE PERMEABILITY OF THE PLACENTA OF THE RAT TO GLYCINE, ALANINE AND UREA

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Abstract
Glycine, alanine and urea were administered by subcutaneous injection to pregnant rats on the 18th or 19th day of gestation. An amount equal to 0.4 gm. N per kgm. of body weight was given in 5 cc. of 0.9% NaCl after a 20 hr. fast. With glycine and alanine, the amino N content of the whole fetus and of the maternal muscle and liver rose considerably, at similar rates, indicating that the placenta is freely permeable to amino acids. The mechanism by which the maternal muscle absorbs amino acids from the maternal plasma is the same as that by which the fetus absorbs amino acids from the fetal plasma; namely, diffusion. The fact that at birth the fetal plasma has a higher concentration of amino acids than the maternal plasma may be due to its lower pH value and consequent influence on the distribution across the placenta] membrane. Injection of urea led to a large increase in urea in the fetus and in the maternal muscle and liver.

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