Muscle chemoreflex increases renal sympathetic nerve activity during exercise

O’Hagan, Kathleen P., Susan M. Casey, and Philip S. Clifford. Muscle chemoreflex increases renal sympathetic nerve activity during exercise. J. Appl. Physiol. 82(6): 1818–1825, 1997.—Activation of the muscle chemoreflex increases sympathetic drive to skeletal muscle in humans. This study investigated whether activation of the muscle chemoreflex augments the renal sympathetic nerve activity (RSNA) response to dynamic exercise in rabbits. The muscle chemoreflex was evoked by hindlimb ischemia during exercise on a motorized treadmill. Seven New Zealand White rabbits performed a nonischemic control protocol and a hindlimb ischemia protocol in which terminal aortic blood flow (Q˙ta) was reduced to 51 ± 2% of preocclusion Q˙ta by partial aortic occlusion after 1.5 min of exercise. Mean arterial pressure (MAP), heart rate, RSNA andQ˙ta increased in response to exercise and were similar between trials during the first 1.5 min of exercise. In the control trial, Q˙ta, MAP, and RSNA were stable at an elevated level through an additional 3.5 min of exercise. Hindlimb ischemia produced a potent pressor response that plateaued after 2.5 min (Δ+17 ± 4 mmHg, where Δ designates change). RSNA began to increase after 1.5 min of ischemic exercise and was significantly elevated relative to preocclusion RSNA at 2.5 (Δ+25 ± 9%) and 3.5 (Δ+47 ± 12%) min of occlusion. These results suggest that the muscle chemoreflex can augment sympathoexcitatory drive to the kidney during dynamic exercise.