Effect of excess phenylalanine diet during pregnancy on fetal brain growth in rats.

The effects of 10 and 20% casein diets containing 7% phenylalanine (Phe) during pregnancy on fetal brain growth were examined in rats. Control pregnant rats were fed the casein diets ad libitum or in restricted amounts. Total food intakes during 21-day period in the Phe excess groups decreased to about 50% of those of the liberally fed control groups. In control rats given 10 and 20% casein diets, fetal brain weights (Y, mg) were significantly and hyperbolically correlated to total food intakes (g/21 days), conforming to the following equations: Y = -10283/X + 130.5 (n: 13, r = 0.89, p < 0.001) and Y = -4396/X + 130.4 (n: 15, r = 0.68, p < 0.005), respectively. Similar plots for rats fed 10 and 20% casein diets with Phe fell below these lines, meaning that fetal brain growth was impaired by both the decreased food intake due to excess Phe (nonspecific effect) and the toxicity of excess Phe per se (specific effect). Total amounts of RNA and protein and protein/DNA ratio decreased in the fetal brain from excess Phe dams, suggesting that protein synthesis of brain cells was disturbed. This may be partly due to the disruption of normal patterns of free amino acids observed in the fetal brains. Reduction of total DNA was also seen in fetal brain from excess Phe groups, meaning impaired proliferation. From above findings we concluded that proliferation and hypertrophy were impaired in fetal brain from excess Phe dams.