AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 4 756-R760, Copyright © 1993 by American Physiological Society
Plasma epinephrine appearance and clearance rates in fetal and newborn sheep
H. Stein, K. Oyama, A. Martinez, B. Chappell and J. Padbury
Department of Pediatrics, Harbor-UCLA Medical Center, School of Medicine, Torrance 90502.
Newborn plasma catecholamine levels are elevated compared to fetal life.
Whether this reflects increased catecholamine secretion after birth or
decreased clearance is not known. To determine the plasma appearance and
clearance rates for catecholamines during the transition to postnatal life,
we compared plasma epinephrine appearance and clearance rates in fetal
sheep before birth and in newborns after delivery. Plasma epinephrine
appearance and clearance rates were measured by radiotracer analysis in
eight fetuses at 127 +/- 1 days of gestation and, after cesarean delivery,
at 130 +/- 1 days of gestation. There was no difference in plasma
epinephrine appearance rate during the fetal (26 +/- 4 ng.kg-1 x min-1) or
newborn studies (31 +/- 5 ng.kg-1 x min-1). The fetal plasma epinephrine
clearance rate (131 +/- 13 ml.kg-1 x min-1) was significantly higher than
newborn plasma epinephrine clearance rate (40 +/- 3 ml.kg-1 x min-1). Thus
fetal plasma epinephrine appearance rate is not different from appearance
rate in the immediate newborn period when catecholamine levels are higher
than during most other physiological circumstances. The increase in
circulating catecholamine levels at birth is due in part to a significant
decrease in clearance rate. It is likely that removal of the placental
contribution to whole body clearance accounts for much of the difference
observed in fetal and newborn clearance rates.
