The determinations of the amino acid pools, including tryptophan (by fluorescence spectrometry), in the arterial and venous blood of the mother, the arterial and venous blood of the fetus (cord blood), the amniotic fluid and the placenta was done in eight women at the moment of delivery. Only nine amino acids (asp, try, met, phe, ser, cys, lys, gly, thr) were significantly retained and four (arg, glu, pro and glu-NH₂) were significantly released by the fetal tissues. In contrast with this behavior most amino acids were retained by the maternal tissue, try, phe and hist showing the highest retention. When the amino acids are grouped as essential and nonessentials, the maternal tissues retained both categories without apparent discrimination, while the fetal tissues retained essential amino acids preferentially. Our results emphasize the importance of the placenta as the regulating system of the fetal milieu under normal conditions. Thus human fetal blood levels of amino acids are patterned after the placental ones and not after the maternal values obtained at the same time. It is apparent that the placenta seems to function as a nonspecific retention filter for outgoing amino acids, but that its function is selective in respect to the release of amino acids into the fetal circulation.

Complete placentas and membranes were obtained from women after uncomplicated singleton pregnancies. Six were collected after labour at term, six after preterm labour and six after elective Caesarean section at term. Leukotriene C4 (LTC4), leukotriene D4 (LTD4) and leukotriene E4 (LTE4) release was examined using a short-term incubation technique. Release by amnion was significantly higher than that by the other tissues for the three modes of delivery. Comparison of LTC4, LTD4 and LTE4 release by individual tissues with regard to the type of delivery showed no significant difference.

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Placentas were obtained at the moment of delivery from mother-infant pairs comprising 35 small for gestational age infants with intrauterine growth retardation (considered as intrauterine malnutrition, [IUM]), 28 prematurely born, but of appropriate size for gestational age (AGA), and 17 normal full-term (FT) infants. The placentas were chilled and perfused immediately, aliquots were analyzed for DNA, RNA, protein/DNA, some enzymes, and adenine nucleotide contents. Body weight of the infants at birth was directly correlated with placental weight. Placentas of IUM and ACA infants were of similar size, and were smaller than FT placentas. Nuclear (DNA) and cytoplasmic (RNA) contents of the IUM placentas were smaller, but cell size (prot/DNA) was larger than FT placentas. Cytoplasmic mass (RNA/DNA) of IUM placenta was largest. There was a direct linear correlation between cell size and cytoplasmic mass in all groups. Pyruvic (PK) and adenylic kinase (AK) activities of IUM placentas were equal to those of FT and higher than the AGA. In all groups PK activity correlated with birth weight. ADP and ATP levels of IUM placenta were similar to those of the FT, but greater than the AGA. AMP content of IUM placentas was lower than FT; but higher than AGA. Apparently the metabolic features of the small IUM placentas do not differ appreciably from those of FT infants, in contrast to previously demonstrated differences in cord blood and maternal leukocytes. The low values found for AGA infants suggest that the parameters of placental metabolism which we studied reflect gestational age. Except for the reduced DNA content, but larger cytoplasmic mass, the metabolic components of the placenta after 38 weeks do not reflect the prior growth process of the fetus, in contrast to metabolism of the maternal or fetal leukocytes, which may be an index of fetal growth.