Regional conductance changes during hemorrhage in pregnant and nonpregnant conscious rabbits

Pregnant animals are less able to maintain arterial blood pressure (BP) during hemorrhage (H). Because BP is initially maintained by reflex vasoconstriction, this study tested the hypothesis that reflex decreases in vascular conductance (CON) are attenuated during pregnancy. Rabbits were instrumented with arterial and venous catheters and flow probes around the distal aorta (HQ; n=7), renal artery (REN; n=5) and/or mesenteric artery (MES; n=3). Rabbits were bled via the venous catheter at 2% of the initial blood volume (BV) per min before (NP) and at the end of pregnancy (P). Before H, BP was lower in P rabbits (67±3 vs. 59±2 mmHg; p<0.05). After 25% BV loss, BP decreased to 47±5 mmHg (p<0.01) in P rabbits, but was not altered in NP rabbits. HQ CON was higher before H in P rabbits (1.9±0.1 vs. 1.0±0.1 ml/min/mmHg; p<0.001). However, HQ CON decreased to 81±3% of control (p<0.01) after 10% BV loss in NP rabbits, but did not decrease until 20% BV loss in P rabbits. Before H, MES CON was higher during P (1.29±0.31 vs. 0.75±0.07 ml/min/mmHg; p<0.05), but REN CON was not different between groups (0.42±0.03 vs. 0.37±0.04 ml/min/mmHg). MES CON did not decrease during H in either group. REN CON also did not change initially in NP rabbits, but decreased (p<0.05) after 20% BV removal in P rabbits. In summary, HQ reflex vasoconstriction is reduced in P rabbits, which may explain in part the lesser ability to maintain BP during H.