The effects of maternal protein restriction on the growth of the rat fetusand its amino acid supply

Maternal protein deficiency causes fetal growth retardation which has been associated with the programming of adult disease. The growth of the rat fet us was examined when the mothers were fed on diets containing 180, 90 and 6 0g protein/kg. The numbers of fetuses were similar in animals fed on the 18 0 and 90g protein/kg diets but the number was significantly reduced in the animals fed on the 60 g protein/kg diet. The fetuses carried by the mothers fed on the 90 g protein/kg diet were 7.5 % heavier than those of mothers f ed on 180g protein/kg diet on day 19 of gestation, but by day 21 the situat ion was reversed and the fetuses in the protein-deficient mothers were 14 % smaller. Analysis of the free amino acids in the maternal serum showed tha t on day 19 the diets containing 90 and 60 g protein/kg led to threonine co ncentrations that were reduced to 46 and 20 % of those found in animals fed on the control (180g/kg) diet. The other essential amino acids were unchan ged, except for a small decrease in the branched-chain amino acids in anima ls fed on the 60g protein/kg diet. Both low-protein diets significantly inc reased the concentrations of glutamic acid+glutamine and glycine in the mat ernal serum. On day 21 the maternal serum threonine levels were still reduc ed by about one third in the group fed on the 90g protein/kg diet. Dietary protein content had no effect on serum threonine concentrations in nonpregn ant animals. Analysis of the total free amino acids in the fetuses on day 1 9 showed that feeding the mother on a low-protein diet did not change amino acid concentrations apart from a decrease in threonine concentrations to 4 5 and 26 % of the control values at 90 and 60 g protein/kg respectively. Th e results suggest that threonine is of particular importance to the protein -deficient mother and her fetuses. Possible mechanisms for the decrease in free threonine in both mother and fetuses and the consequences of the chang e in amino acid metabolism are discussed.