Reflex effects of thermal stimulation on sympathetic nerve activity to skin and kidney

Effects of peripheral and central thermoreceptor reflexes on sympathetic nerve activity to the skin (SkNA) and kidney (RNA) were compared in anesthetized cats. Sudden warming of the skin produced a rapid increase of RNA, wheras sudden cooling produced a rapid increase of SkNA. When the bath temperature (TB) was 17.6, 29.7, and 41.9 degrees C, the normalized SkNA was 100, 82, and 48%, while the normalized RNA was 81, 90, and 100%, respectively. Similarly, under open baroceptor loop conditions, SkNA changed inversely with TB, while RNA changed proportionally to TB. Changes in the temperature of the whole brain including hypothalamus (Thy) modified the amplitude of grouped RNA and SkNA synchronously with the cardiac cycle. At TB of 32.4 degrees C, when Thy was altered in a range of 30-42 degrees C, SkNA reached a maximum level at a Thy of 38.4 degrees C, whereas RNA reached a maximum above 42 degrees C. In a Thy range of 38-42 degrees C, the slopes of the Thy-SkNA curve and Thy-RNA curve were 30 and +4%/degrees C, respectively. At Thy below 38 degrees C, SkNA and RNA changed in parallel with Thy. Continuous cooling of the skin modified the slope of the TB-SkNA curve, but a small change of Thy caused a shift of the TB-SkNA curve.