AJP - Regulatory, Integrative and Comparative Physiology, Vol 256, Issue 5 1040-R1043, Copyright © 1989 by American Physiological Society
Mechanisms of fetal blood volume restoration after slow fetal hemorrhage
R. A. Brace
Department of Reproductive Medicine T-002, University of California, San Diego, La Jolla 92093.
Previous studies have shown that blood volume returns to normal within
24-48 h after hemorrhage in the adult of several species, whereas vascular
volume restoration occurs within 3-4 h after a 2-h hemorrhage of the sheep
fetus. The purpose of the present study was to determine whether an
increase in fetal osmolality and/or circulating plasma protein mass
contribute to the rapid volume restoration in the fetus. Nine chronically
catheterized fetal sheep at 132 +/- 2 days gestation (term = 145-150 days)
were hemorrhaged 30.9 +/- 2.2% of their initial blood volume over 2 h.
Blood volume returned to normal 3 h after the hemorrhage. No change in
fetal osmolality or in the fetal-maternal osmotic gradient occurred during
or after the hemorrhage. However, there was a near-perfect correlation
between blood volume and circulating plasma protein mass during and after
the hemorrhage. Thus the present study provides no evidence for either a
fetal cellular or transplacental source of fluid during fetal
posthemorrhage volume restoration because osmolality was unchanged. Instead
it appears that a rapid redistribution of proteins and fluid from the fetal
interstitial space most likely mediates the vascular volume restoration.
