AJP - Regulatory, Integrative and Comparative Physiology, Vol 254, Issue 4 585-R589, Copyright © 1988 by American Physiological Society
Placental oxygen transport in sheep with different hemoglobin types
R. B. Wilkening, R. D. Molina and G. Meschia
Department of Pediatrics, University of Colorado School of Medicine, Denver 80262.
To study the effect of genetic differences in the maternal oxyhemoglobin
dissociation curve on fetal O2 supply, we compared eight pregnant ewes
homozygous for high O2 affinity hemoglobin (A) with eight pregnant ewes
homozygous for low O2 affinity hemoglobin (B). Each ewe carried a single
fetus. Fetal weights were not significantly different (A, 3,000 +/- 170 g;
B, 3,070 +/- 270 g). The A ewes had significantly higher arterial O2
saturation (95 vs. 89.4%), uterine blood flow per kilogram of fetus (464
vs. 374 ml/min), uterine venous O2 saturation (78.1 vs. 67.5%), and
placental-to-fetal weight ratio (0.107 vs. 0.085). Uterine venous PO2 was
significantly less in A ewes (41.7 vs. 47.6 Torr), but umbilical venous and
arterial PO2 and fetal O2 uptake were virtually equal in the two groups. We
conclude that the difference in O2 affinity between A and B hemoglobins is
fully compensated for by differences in arterial O2 saturation, in the rate
of perfusion of the pregnant uterus, and in the degree of PO2 equilibration
between the uterine and umbilical circulations so that the single fetuses
of A and B hemoglobin carriers have equal levels of oxygenation.
