Placental norepinephrine clearance: in vivo measurement and
physiological role.
Bzoskie, Lisanne, Leslie Blount, Kent Kashiwai, Yi - Tang Tseng,
William W. Hay, Jr, James F. Padbury.
Perinatal Research Laboratories, Department of Pediatrics, Harbor
-UCLA Medical Center, 1124 West Carson St., Torrance, CA, 90502,
Division of Perinatal Medicine and Research, University of Colorado
School of Medicine, 4200 East Ninth Avenue, Denver, CO, 80262
APStracts 2:0054E, 1995.
The intrauterine clearance rate of catecholamines is higher than in
newborn animals or in adults. The separate contributions of the fetus
and placenta to this clearance are not known. The placenta is a site
of expression of the amine plasma membrane transporters which mediate
this process. In order to determine the physiological role of this
placental transporter in vivo, we studied fetal sheep at 123 days
with common umbilical vein (UV), fetal arterial (AO) and venous
catheters. Tritiated norepinephrine (3H-NE) was infused to determine
the kinetics of placental and fetal norepinephrine appearance and
clearance rates. Umbilical flow was determined by tritiated water
infusion. Placental and total (fetal-placental) NE clearance rates
were determined by measurement of 3H-NE from simultaneously drawn UV
and AO samples. Total clearance was 99 +/- 8 ml/kg/min. Placental
fractional 3H-NE extraction was 21% and accounted for 48% of total
clearance. Fetal plasma NE production rate was 85 +/- 20 ng/kg/min.
We conclude that placental catecholamine clearance is an important
metabolic function of the placenta. This mechanism for clearance of
the high fetal production rate of catecholamines is vital for fetal
homeostasis. We speculate that derangements in placental
catecholamine clearance may explain the exaggerated adverse effects
on the fetus of drugs like cocaine which block catecholamine
transport.
Received 31 October 1994; accepted in final form 3 March 1995.
APS Manuscript Number E446-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 4 April 1995.