Influence of carotid baroreceptors on vascular responses to carotid chemoreceptor stimulation in the dog.

The modification by the carotid baroreceptors of the vascular responses to chemoreceptor stimulation was studied in anesthetized, artificially ventilated, vagotomized dogs. The carotid bifurcations were vascularly isolated and perfused with blood at constant pressures of 134, 215, and 51 mm Hg to cause intermediate, maximal, and minimal inhibition, respectively, of the vasomotor center. At each pressure, stimulation of the carotid chemoreceptors was achieved by perfusion with hypoxic hypercapnic blood. With intermediate inhibition, the chemoreceptor stimulation increased the aortic pressure by 50% and decreased the hind-limb and kidney blood flow (perfusion at constant pressure) by 59% and 19%, respectively. At carotid sinus pressures of 215 and 51 mm Hg, the effects of chemoreceptor stimulation were absent or markedly attenuated. With intermediate sinus pressure, chemoreceptor stimulation decreased the perfusion pressure of the saphenous vein by 27% (perfusion at constant flow). When the sinus pressure was increased to 215 mm Hg, the tone of the vein did not change, but chemoreceptor stimulation was without effect. The present study indicates a central interaction (which may be presynaptic) between the chemoreceptor and baroreceptor inputs such that the vascular responses to chemoreceptor stimulation are inhibited when the carotid sinus activity is maximal or minimal.