Arterial baroreceptor function in differential cardiovascular adjustments induced by central thermal stimulation.

Dogs were anesthetized with sodium pentobarbital, relaxed with succinyl choline and were kept under artificial ventilation. Both carotid bifurcations were denervated and the Vagus nerves were cut in the neck. Regional blood flow in the skin and the intestine, cardiac output, heart rate and arterial pressure were determined before, during and after spinal cord heating and cooling. Further experiments were performed in which, in addition, sympathetic effects on the heart were excluded by exstirpation of the caudal cervical and stellate ganglia or by beta-receptor blockade. The cardiovascular responses were compared with those obtained in a preceding investigation from dogs with intact baroreceptors and vagus nerves. As in intact dogs, appropiate thermoregulatory adjustments of skin blood flow were induced by thermal stimulation of the spinal cord after baroreceptor denervation and vagotomy. However, blood pressure homeostasis was lost. The pattern of cardiovascular ajustments during heating consisted in cutaneous vasodilatation intestinal vasoconstriction and, due to sympathetic activation an increase of heart rate and cardiac output. This pattern was qualitatively identical with that intact animals. During spinal cord cooling the cardiovascular response pattern consisted in cutaneous vasoconstriction, intestinal vasoconstriction and, depending on cooling intensity, a reduced or unchanged sympathetic influence on the heart. This pattern differed considerably from what in intact animals but basic features were still present as indicated by opposite changes of cardiac and vascular sympathetic tone during cooling. It is concluded that the baroreceptor signals play no primary role in the generation of differential vasomotor responses under the present experimental conditions. This confirms assumptions made on the basis of observations in animals with intact baroreceptor input. However, baroreceptor signals contribute significantly to blood pressure homeostasis which is normally maintained during spinal thermal stimulation.