CONTRIBUTION OF THE HINDLIMB VASCULATURE TO SYSTEMIC RESISTANCE RESPONSES TO CAROTID SINUS PRESSURE CHANGES IN THE RABBIT

The effects on the vascular resistance of the skinned hindlimb of changes in pressure within the vascularly isolated carotid sinus have been compared with those on systemic vascular resistance in the same rabbits. With the hindlimb perfused at arterial pressure a reduction of sinus pressure from 200 mm Hg to 40 mm Hg increased hindlimb vascular resistance by only 50% compared with an increase of 100% in systemic vascular resistance. Although cardiac output was unaltered, blood flow to the hindlimb increased by 24%. However, flow to the contralateral hindlimb, which had been sympathectomized, rose by 400% and its resistance was halved. These responses to a reduction in sinus pressure show that in the absence of sympathetic tone the hindlimb has a compliant vascular bed and indicate that even though the changes in vascular resistance of the innervated limb were much less than the average systemic resistance change, there must, nevertheless, have been a substantial increase in sympathetic drive to the limb.