The transfer of free alpha-amino nitrogen across the placental membrane in the guinea-pig.

1. Transfer of endogenous alpha-amino nitrogen from the maternal to foetal side of the placental membrane was studied in the foetal guinea-pig placenta perfused, in situ via the umbilical vessels, with an artificial fluid. Changes in maternal placental blood flow were followed by measuring the transfer of antipyrine into the perfusate.2. Active transport by the membrane was demonstrated under these conditions by observing the increased ratio of L/D leucine appearing in the perfusate in comparison with the maternal plasma ratio.3. Reduction in maternal placental flow following haemorrhage was associated with a fall in transfer of amino nitrogen to about half of the control values.4. The concentration of alpha-amino nitrogen in the perfusate was inversely proportional to the foetal placental flow which had a smaller influence on amino nitrogen transfer per min than did the maternal blood flow.5. Hypoxia and some inhibitors of oxidative metabolism were without influence on the transfer of alpha-amino nitrogen in this preparation.