The influence of perfusate temperature on the responses of a superficial vein in the carotid baroreceptor reflex in dogs

In chloralose-anaesthetised dogs, both vagus nerves were cut and both carotid sinuses vascularly isolated and perfused with blood. The left hind limb was vascularly isolated and the femoral artery and the central end of a superficial metatarsal vein were perfused at constant flows with blood from an oxygenator. Femoral venous pressure was held constant. Arterial and venous responses were determined by measuring changes in arterial perfusion pressure and in the pressure gradient between the superficial metatarsal and femoral veins. Large step increases in carotid sinus pressure resulted in an average decrease in venous gradient of 5.6% when the temperature of the venous perfusate was 38° C and a significantly (P<0.01) greater response (8.8%) when the perfusate was at 31° C. When the venous perfusate was cooled from 38 to 31° C, venous gradient increased by averages of 89% when carotid pressure was low, 64% when carotid pressure was high and 32% after lumbar sympathectomy. These responses are significantly different from each other (P<0.05). It is concluded that the reflex responses of the superficial vein to maximal stimulation of the baroreceptors were small but they were significantly potentiated by cooling the perfusate. The venous constriction in response to cooling was reduced by raising the carotid pressure and further reduced by surgical sympathectomy.