Effect of Ovarian Steroids on Maintenance of Pregnancy in Rats Fed Diets Devoid of One Essential Amino Acid

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Abstract
Pregnancy maintenance in rats fed various diets lacking one essential amino acid was examined. In groups where fetal resorption was observed, the effect of ovarian steroids on maintenance was also investigated. Fetal wastage occurred in pregnant rats by feeding diets devoid of any one essential amino acid other than lysine: the rats fed a lysine-free diet showed food intake comparable to control animals and maintained pregnancy. In valine or isoleucine deficiency, complete loss of the fetuses was observed. Daily administration of 0.5 µg of estrone and 4 mg of progesterone prevented fetal losses due to these diets. Uterine total RNA, DNA and the RNA/DNA ratio in rats in which pregnancy was maintained were higher than in those in which it was not, while the DNA concentration in the rats failing to maintain pregnancy was significantly higher than in the animals maintaining pregnancy. The hepatic RNA/DNA ratio was increased by steroid injection, while that in muscle was decreased. The placental RNA/DNA ratios in deficient rats were comparable with those in control animals. The concentrations of all essential amino acids, except lysine and threonine, in liver, muscle, plasma and placenta of all deficient rats were maintained at control levels, although the diets lacked one essential amino acid. Mechanisms involved in maintenance of pregnancy are discussed.