Mechanisms of amino acid supply to the rat conceptus in normal and abnormal development

Using in vitro and in vivo models, we have shown that protein is an important source of amino acids from 8.5 to 17.5 d postconception, a significant portion of postimplantation development in the rat. This satisfactorily explains why inhibition of protein pinocytosis and digestion by the visceral yolk sac may lead to congenital malformations, growth retardation, and intrauterine death during organogenesis and growth retardation and death during fetal stages. In humans, this process may be just as important and possibly just as vulnerable to inhibition, but other placental or paraplacental tissues may be involved in addition to the secondary yolk sac.