Skin arteriolar responses to local temperature changes in hypertensive rats

A rat skin preparation was developed to determine if the responses of the resistance vessels to local skin warming and cooling were abnormal in spontaneously hypertensive rats (SHR). A major advantage of this preparation is that all the skin resistance vessels from small arteries preceding the microcirculation to small arterioles can be studied by intravital microscopy techniques. An abdominal skin flap was reflected with intact vasculature and positioned on a temperature-controlled manifold. Diameters of small arteries and large through small arterioles were measured at normal skin temperature (35 degrees C) and after cooling to 25 degrees C and warming to 38 degrees C, there were no differences in control diameters for comparable branching orders between normotensive (Wistar-Kyoto) and hypertensive rats; however, the maximum diameter of small arteries was 13% smaller in hypertensive rats. All arteriolar branching orders possessed vascular tone that was not altered by neural blockade with tetrodotoxin. With cooling to 25 degrees C, all branching orders constricted (range, 12-37%). The largest and smallest vessels of hypertensive rats constricted almost twice as much as their normotensive counterparts. With warming to 38 degrees C, only the smallest arterioles dilated (19% in normotensive versus 43% in hypertensive rats). This study demonstrates major differences in the arteriolar branching orders that respond to local warming and cooling of nonapical skin regions in both normotensive and hypertensive rats and also shows that skin arterioles in SHR are more responsive to local temperature changes.