Submitted on September 23, 2003
Accepted on November 7, 2003
Reciprocal inhibition of umbilical uptake within groups of amino acids
Maciej Jozwik1, Cecilia Teng2, Randall B. Wilkening2, Giacomo Meschia2*, and Frederick C. Battaglia2
1 Department of Gynecology, Medical University of Bialystok, Bialystok, Poland
2 Division of Perinatal Medicine, Department of Pediatrics, University of Colorado Health Sciences Center, Aurora, CO, USA
* To whom correspondence should be addressed. E-mail: Barbara.Falk{at}UCHSC.edu.
Eight pregnant sheep were infused with two amino acid mixtures of different
composition: essential amino acids only, and the essentials plus some of the
nonessentials. Uterine and umbilical uptakes of amino acids were measured before
and during infusion. For most of the amino acids, the infusion increased both
maternal plasma concentration and umbilical uptake. However, depending upon the
infusate composition, the increase in maternal concentration of some amino acids
was associated with no change or a significant reduction in umbilical uptake. Data
were pooled from this and other similar studies to test the hypothesis that the
umbilical uptake of several amino acids can be inhibited by co-infused amino acids.
The test consisted of fitting the data, by means of multiple regression analysis, to the
linear transformation of a saturation kinetics equation in which uptake is assumed to
depend on maternal arterial concentrations. The analysis showed significant
inhibitory effects within the neutral essential amino acids group and within the lysine-arginine
group, with no demonstrable interaction between the two groups. Uterine
uptakes did not show clear evidence of saturability and inhibitory interactions
suggesting a large transport capacity and low transporter affinity on the maternal
surface of the trophoblast. We conclude that the transport of any given amino acid
from placenta to fetus is a function of both its own maternal concentration and the
maternal concentration of inhibitory amino acids.
