Amniotic fluid (AF) contains free
amino acids that enter via transplacental and transmembranous routes from maternal sources; subsequently, the developing fetus "ingests" these
amino acids early in gestation through unkeratinized skin and later through continuous AF swallowing. Our objectives were as follows: 1) to determine whether a restriction of maternal dietary
glucose modulates the free AF
amino acid pool, and 2) to establish whether any diet-induced changes were predictive of
fetal weight near term (d 21.5). To produce varying in utero growth rates, pregnant rat dams were fed varying levels of
glucose (0, 12, 24, 60%) throughout pregnancy. AF samples, collected on gestational days 18-21, were precolumn derivatized by 9-fluorenylmethyloxychloroformate to produce stable primary and secondary
amino acid derivatives required for HPLC detection at low
amino acid concentrations. Eighteen
amino acids were identified. A 2-way ANOVA with main effects of diet (< or =12% and > or =24%
glucose) and gestational age (d 18/19 and 20/21) showed that 2 AF
amino acids,
methionine and
phenylalanine, and 12 AF
amino acids were independently modified by diet and gestational age, respectively. Of note were the 364% increase in AF
methionine and the constant decline in AF
taurine as both gestational age lengthened and
fetal weight increased. Multiple regression demonstrated that in addition to
methionine, 3 specific AF
amino acids,
cysteine,
lysine, and
tyrosine, predicted
fetal weight. These results demonstrate that the AF
amino acid pool can be modified by the
glucose content of the maternal diet and that specific AF
amino acids are associated with gestational age and fetal growth.