HUMAN FETAL GROWTH RETARDATION: III. PROTEIN, DNA, RNA, ADENINE NUCLEOTIDES AND ACTIVITIES OF THE ENZYMES PYRUVIC AND ADENYLATE KINASE IN PLACENTA

Abstract

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.