The passage of urea and creatinine across the placenta of the pig.

WITH ONE PLATE I T is generally considered that urea diffuses freely across the placental barrier and that creatinine does so too (Needham, 1931), and that the concentration of both compounds is the same in foetal and maternal plasma. Alexander, Nixon, Widdas, & Wohlzogen (1958), however, found that the concentration of creati-nine was higher in the serum of the foetal lamb than it was in the maternal serum. The concentration of creatinine in the serum of the sow during farrowing, and of her piglets at birth Sow 1 Piglet a b c d e Sow 2 Piglet a b Serum creatinine The authors made no specific comment upon this. McCance & Widdowson (1953) discussed the difficulties which would arise if all the chromogens reacting with alkaline picrate in human cord serum were accepted as creatinine, and in work still to be published these two authors found that the concentration of creatinine 'chromogens' in the serum of the foetal pig at term was always higher than in the maternal serum, although the concentrations of urea were the same.