Reflex response of the rabbit hind-limb muscle vascular bed to baroreceptor stimulation and its modification by pregnancy.

1. The pressure--flow relationship of the blood-perfused skinned hind limb has been compared in primigravid pregnant and virgin non-pregnant rabbits while pressure within the vascularly isolated carotid sinus was held at a series of non-pulsatile values. 2. At each level of sinus pressure the slope of the pressure--flow relationship was steeper in the pregnant animals. Thus, at all but the very lowest flows, the same flow was achieved at a lower perfusion pressure in the pregnant rabbits. 3. When hind-limb vascular resistance at constant flow was plotted against carotid sinus pressure it could be seen that at each level of sinus pressure vascular resistance was less in the pregnant rabbits. 4. The reflex responses of the hind-limb bed to changes in sinus pressure were compared in pregnant and non-pregnant animals; there was little difference in the threshold and saturation values of carotid sinus pressure. There seemed to be a small reduction in the range and gain of the reflex in the pregnant group but this was not statistically significant. 5. We have previously shown total peripheral resistance in the pregnant rabbit to be less than that in the non-pregnant rabbit at the same level of sinus pressure. The lower hind-limb vascular resistance of the pregnant rabbit at any given sinus pressure must contribute to this reduced total peripheral resistance.