The present review focuses on the physiological functions of
glutamate-
glutamine exchange involving placental
amino acid transport and umbilical
amino acid uptake in mammals (particularly in sows), with special emphasis on the associated regulating mechanisms.
Glutamate plus
glutamine are among the most abundant and the most utilized
amino acids in fetus during late gestation. During pregnancy,
amino acids, notably as precursors of macromolecules including
proteins and
nucleotides are involved in fetal development and growth.
Amino acid concentrations in fetus are generally higher than in the mother. Among
amino acids, the transport and metabolism of
glutamate and
glutamine during fetal development exhibit characteristics that clearly emphasize the importance of the interaction between the placenta and the fetal liver.
Glutamate is quite remarkable among
amino acids, which originate from the placenta, and is cleared from fetal plasma. In addition, the flux of
glutamate through the placenta from the fetal plasma is highly correlated with the umbilical
glutamate delivery rate.
Glutamine plays a central role in fetal
carbon and
nitrogen metabolism and exhibits one of the highest fetal/maternal plasma ratio among all
amino acids in human and other mammals.
Glutamate is taken up by placenta from the fetal circulation and then converted to
glutamine before being released back into the fetal circulation. Works are required on the
glutamate-
glutamine metabolism during late pregnancy in physiological and pathophysiological situations since such works may help to improve fetal growth and development both in humans and other mammals. Indeed,
glutamine supplementation appears to ameliorate
fetal growth retardation in sows and reduces preweaning mortality of piglets.