Mechanism of clearance and transfer of dipeptides by perfused human
placenta .
Adibi, Siamak A., Steven Schenker, and Emile Morse.
Clinical Nutrition Research Unit,Department of Medicine, University
of Pittsburgh School of Medicine, Division of Gastroenterology and
Nutrition, Department of Medicine, The University of Texas Health
Science Center at San Antonio, and Audie L. Murphy Memorial Veteran's
Hospital
APStracts 3:0103E, 1996.
Glycylglutamine (Gly-Gln) is a stable source of glutamine for
parenteral nutrition. Presently, we have investigated whether this
dipeptide is transferred intact across the human placenta. Although
after 90 minutes of placental perfusion, there was almost complete
disappearance of Gly-Gln (100 [mu]M) from the maternal compartment,
only a small concentration of this dipeptide (<6 [mu]M) appeared
in the fetal compartment. To investigate whether this transfer was
due to transcellular transport, brush border membrane vesicles of the
human placenta were probed with 3H-Gly-Gln which showed no uptake. To
investigate whether hydrolysis was the mechanism of disappearance of
Gly-Gln, the perfusion study was repeated with glycylsarcosine (Gly
-Sar), which is resistant to hydrolysis. In sharp contrast to Gly-Gln,
after 90 minutes of perfusion, nearly 80% of Gly-Sar remained in the
perfusate (half-life of 24 vs. 235 minutes). The rest of the Gly-Sar
was recovered intact in the fetal compartment. The addition of Gly
-Gln to the maternal compartment increased the accumulation of
glycine, but not glutamine, in both the maternal and fetal
compartments. In conclusion, our data suggests that a) the mechanism
of clearance of Gly-Gln by perfused human placenta is largely
hydrolysis while that of Gly-Sar is largely passive diffusion and b)
the placenta has a greater preference for glutamine than for glycine.
Received 16 November 1996; accepted in final form 3 May 1996.
APS Manuscript Number E26-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 May 96