Effect of maternal dietary restriction on fetal growth and placental transfer of alpha-amino isobutyric acid in rats.

Maternal net weight gain, plasma clearance, and placental and fetal accumulation of I.V. administered 14C-alpha amino isobutyric acid (AIB) on day 20 of gestation were measured in pregnant rats: 1) fed ad libitum throughout gestation (Control), 2) fed 50% of the normal daily food intake during the last week of gestation (catabolic phase), and 3) fed 50% of the normal daily food intake throughout gestation. Dietary restriction during the catabolic phase only resulted in a loss of 54% of the net maternal weight gained during the first two weeks of gestation, while dietary restriction throughout gestation resulted in a net loss of 5.4% of the dams prepregnant weight. Both dietary regimens caused significant growth retardation of the fetus. Maternal plasma clearance of AIB was rapid and occurred at the same rate in all three groups. Placental accumulation and transfer of AIB to the fetus was reduced relative to the controls only in dams fed the restricted diet throughout gestation. Fetal to placental AIB concentration ratios were similar for each group indicting no difference in ability of placentas to release amino acid into the fetal circulation. The results indicate that mechanisms other than reduced nutrient transfer may be responsible for fetal growth retardation induced by maternal malnutrition during the catabolic phase of pregnancy only.