Effect of exercise muscle temperature on renal and sympathetic responses to isometric exercise in humans

Abstract chapter 2. The purpose of the present study was to examine the effect of heating and cooling the forearm muscles on renal vascular responses to ischemic isometric handgrip (IHG). It was hypothesized that heating and cooling the forearm would augment and attenuate renal vascular responses to IHG, respectively. Renal vascular responses to IHG were studied during forearm heating at 39 °C (n=15, 26+/-1 yr) and cooling at 26 °C (n=12, 26+/-1 yr). For a control trial subjects performed the experimental protocol while the forearm was normothermic (∼34 °C). Muscle temperature (measured by intramuscular probe) was controlled by changing the temperature of water cycling through a water-perfused sleeve. The experimental protocol was: 3-min baseline, 1 min of ischemia, ischemic IHG to fatigue, and 2 min of postexercise muscle ischemia. At rest, renal artery blood velocity (RBV; Doppler ultrasound) and renal vascular conductance (RVC; RBV/mean arterial blood pressure) were not different between normothermia and the two thermal conditions. During ischemic IHG there were greater decreases in RBV and RVC in the heating trial. However, RBV and RVC were similar during postexercise muscle ischemia during heating and normothermia. During cooling, RVC decreased less compared to normothermia during ischemic IHG. During postexercise muscle ischemia, RVC was greater during cooling compared to the normothermic trial. These results indicate that heating augments mechanoreceptor-mediated renal vasoconstriction whereas cooling blunts metaboreceptor-mediated renal vasoconstriction.;Abstract chapter 4. This study examined if ACE-inhibition alters central hemodynamic, vascular, and sympathetic responses to isometric handgrip with a normothermic or hyperthermic forearm. Eight male (25+/-2yr) subjects were given an ACE-inhibitor (20 mg of quinapril) or placebo on alternate visits. Subjects performed ischemic isometric handgrip and postexercise muscle ischemia with the forearm muscle normothermic (∼35+/-0.3 °C, intramuscular probe) and hyperthermic (∼38+/-0.3 °C). Blood pressure, heart rate, renal blood flow velocity (Doppler ultrasound), calf blood flow, and muscle sympathetic nerve activity (MSNA) were recorded throughout all studies. Quinapril lowered mean arterial blood pressure (∼8+/-3 mmHg) at baseline, but did not alter cardiovascular and MSNA responses to normothermic isometric handgrip or postexercise muscle ischemia. Exercise with a hyperthermic forearm augmented increases in blood pressure, renal vasoconstriction, and MSNA during both treatments, but there were no significant differences between drug treatments. Likewise, central hemodynamic, vascular, and MSNA responses to postexercise muscle ischemia during heating were not significantly different between drug treatments. These findings suggest ACE-inhibitor-induced changes in the renin-angiotensin and kallikrein-kinin systems do not alter central hemodynamic, vascular, and MSNA responses to isometric exercise in healthy humans.;Abstract chapter 3. The purpose of the study was to determine the interactive effect of aging and forearm muscle heating on renal blood flow and muscle sympathetic nerve activity during ischemic isometric handgrip. A tube lined water-perfused sleeve was used to heat the forearm in twelve young (27+/-1 yr) and nine older (63+/-1 yr) subjects. Ischemic isometric handgrip was performed before and after heating. Muscle temperature (intramuscular thermistor) was 34.3+/-0.2 °C and 38.7+/-0.1 °C during normothermia and heating, respectively. At rest, heating had no effect on renal blood velocity (Doppler ultrasound) or renal vascular conductance in either group (young, n = 12; older, n = 8). During ischemic isometric handgrip, heating caused a significantly greater decrease in renal blood velocity and increase in renal vasoconstriction in both groups compared to normothermia. However, the increase in renal vasoconstriction during heating was greater in the older subjects (18+/-3% at fatigue) compared to the young (8+/-3% at fatigue). Unlike the younger group, heating increased renal vasoconstriction during postexercise muscle ischemia in the older group. During handgrip, heating elicited comparable increases in muscle sympathetic nerve activity responses in both groups (young, n = 12; older, n = 6). The interaction of aging and muscle heating did not alter muscle sympathetic nerve activity responses to exercise. In summary, aging augments renal vascular responses to ischemic isometric handgrip during heating of the muscle that is not associated with greater muscle sympathetic nerve activity.