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Department of Physiology and Pharmacology, The Oregon Health Sciences University, Portland, Oregon 97201
Late
pregnant (P) conscious rabbits are less able to maintain arterial
pressure during hemorrhage than nonpregnant (NP) animals. This study
tested the hypothesis that the difference is due in part to less reflex
vasoconstriction when the rabbits are P. Rabbits (n = 14) were instrumented with
arterial and venous catheters as well as ultrasonic flow probes around
the superior mesenteric, renal, and/or terminal aortic arteries.
Pregnancy increased (P < 0.05) blood
volume [235 ± 5 (P) vs. 171 ± 3 (NP) ml], terminal aortic conductance [1.88 ± 0.11 (P) vs. 0.98 ± 0.06 (NP)
ml · min
1 · mmHg
1],
mesenteric conductance [1.20 ± 0.19 (P) vs. 0.80 ± 0.05 (NP) ml · min
1 · mmHg
1],
and heart rate [191 ± 4 (P) vs. 162 ± 3 (NP)
beats/min] and decreased arterial pressure [59 ± 1 (P)
vs. 67 ± 2 (NP) mmHg; P < 0.05]. Renal conductance was unaltered. The rabbits were bled in
both the NP and P states at 2% of the initial blood volume per minute
until arterial pressure fell below 45 mmHg. Arterial pressure fell with
less blood loss in P rabbits [28 ± 2% (P) vs. 39 ± 2%
(NP) of initial blood volume; P < 0.001]. Terminal aortic conductance decreased
(P < 0.001) before the pressure fall
in both groups, but the response was reduced in P rabbits. Mesenteric and renal conductances did not change in either group before the blood
pressure fall. During the pressure fall, terminal aortic conductance
increased (P < 0.05) only in NP
rabbits. Mesenteric conductance increased in both groups. In summary,
rabbits in late gestation are less able to maintain arterial pressure
during hemorrhage, at least in part because of reduced vasoconstriction
in tissues perfused by the terminal aorta.
baroreceptor reflex; pregnancy; mesenteric blood flow; terminal aortic blood flow; renal blood flow
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