Impact of exogenous amino acids on endogenous amino compounds in the fluid compartments of the chicken embryo

Plasma, allantoic and amniotic fluid of the 13-day chicken embryo contain numerous free amino acids and related compounds. Of these, 40 were investigated using an HPLC-fluorometric technique. The concentration differences of the amino compounds between the fluid compartments are maintained by three bidirectional barriers, i.e. a blood/allantoic barrier, a blood/amnion barrier and an allantois/amnion barrier. Intraallantoic injection of 4.5 μmol/egg of asparagine (ASN), aspartic acid (ASP), valine (VAL) or serine (SER) revealed a strong allantois/blood barrier for these compounds. In contrast, there was equilibration between allantoic and amniotic fluid for ASN, ASP and SER, and an upward trend of the VAL concentration in the amniotic fluid, due to an `overspill' from the allantois. The injections also affected endogenous amino compounds in all three fluid compartments. Asparagine had the most varied effects, including a strong drop of ten plasma amino acids. After all four types of injection, a number of endogenous amino compounds equilibrated between allantois and the normally hyporegulated amnion. Since allantois and amnion are non-innervated, the selective changes of the barriers and the drop of plasma amino acids must be mediated by so far unidentified humoral messengers.