AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 3 574-R579, Copyright © 1989 by American Physiological Society
Modulation of fetal cardiovascular responsiveness to norepinephrine by autonomic nervous system
R. A. Brace and C. Y. Cheung
Department of Reproductive Medicine, University of California, San Diego, La Jolla 92093.
To determine the extent to which the autonomic nervous system modifies the
fetal cardiovascular responses to exogenous norepinephrine (NE), NE was
infused intravenously (0.39-39 micrograms/min) for 30 min into chronically
catheterized sheep fetuses averaging 132 days gestation. The resulting
changes in arterial pressure, venous pressure, heart rate, and blood volume
were compared between fetuses with and without ganglionic blockade.
Autonomic blockade did not alter the relationship between the rise in NE
concentration and NE infusion rate. In fetuses with a blocked autonomic
nervous system, the arterial pressure response to exogenous NE was shifted
0.8 log units to the left when compared with normal fetuses. The venous
pressure response to NE infusion was not altered in the blocked fetuses
when compared with normal fetuses. Heart rate in the autonomically blocked
fetuses increased with plasma NE concentration, which was opposite to the
initial suppression of heart rate during NE infusion in control fetuses.
Fetal blood volume decreased progressively with increasing NE infusion rate
in the blocked fetuses, which was similar in autonomically intact fetuses,
except for an increase in blood volume at low NE infusion rates. Thus it
appears that the autonomic nervous system modifies the fetal arterial
pressure, heart rate, and blood volume responses to exogenous NE but not
the response of venous pressure.
