Summary
Radioactive microspheres were used to assess the influence of hypothalamic temperature on tissue blood flow and the regional distribution of cardiac output in conscious sheep chronically prepared with hypothalamic thermodes. Hypothalamic heating elicited panting in 6 animals, and in these, blood flow rate increased in respiratory muscles and decreased in the thyroids, kidneys, spleen and gut; cardiac output did not change, but was redistributed in a pattern similar to that seen during spinal cord heating, which differs from that which occurs during exposure to a warm environment. Four other animals did not pant in response to hypothalamic heating, but showed small but definite increases in capillary blood flow in skin of extremities. Reasons for the two different types of response to heating are discussed. The failure to detect increases in microsphere-measured extremity skin blood flow in the first group and only small changes in the second group above, despite the increased skin temperature always seen with hypothalamic heating, is attributed to specific influences of CNS stimulation on arteriovenous anastomoses.
In 6 animals, hypothalamic cooling elicited visible shivering associated with increased oxygen consumption; blood flow rate decreased in skin and increased in respiratory and non-respiratory muscles, fat and the myocardium; cardiac output showed an increase and a redistribution similar to that which occurs during exposure to a cold environment.
Arterial blood pressure was steady, but there were changes in regional vascular resistance. Therefore, and in view of other studies, the blood flow responses observed are attributed to regional differentiation of sympathetic activity.
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Hales, J.R.S., Bennett, J.W. & Fawcett, A.A. Integrated changes in regional circulatory activity evoked by thermal stimulation of the hypothalamus. Pflugers Arch. 372, 157–164 (1977). https://doi.org/10.1007/BF00585330
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DOI: https://doi.org/10.1007/BF00585330