Effects of a protein-free diet on amino acids and sex hormones of rats during the early postimplantation stages of pregnancy.

In rats, the effect of a protein-free diet on the maintenance of gestation was investigated during the early postimplantation stages (days 7 to 10). The growth kinetics of the implantation site, the concentrations of free amino acids in the implantation sites as well as in the maternal liver and the levels of sex hormones in the maternal serum were determined. The results of these studies showed that in the whole implantation site, the absolute amounts of DNA, RNA and nitrogen were significantly lower in the rats fed a protein-free diet, the concentrations of essential amino acids decreased in the whole implantation site to the same extent as in the maternal liver. In the case of the non-essential amino acids, however, a significant increase in the concentrations of some of the amino acids was observed in the maternal liver. With regard to the essential amino acid pool, it appears that the liver and decidua can be regarded as being in a dynamic equilibrium. Peripheral prolactin and progesterone concentrations significantly decreased on day 8 of gestation, while the amounts of LH and total oestrogens remained unchanged.