Muscle chemoreflex increases renal sympathetic nerve activity during exercise

O'Hagan, Kathleen P., Susan M. Casey, and Philip S. Clifford. Muscle chemoreflex increases renalsympathetic nerve activity during exercise. J. Appl.Physiol. 82(6): 1818-1825, 1997.Activation ofthe muscle chemoreflex increases sympathetic drive to skeletal musclein humans. This study investigated whether activation of the musclechemoreflex augments the renal sympathetic nerve activity (RSNA)response to dynamic exercise in rabbits. The muscle chemoreflex wasevoked by hindlimb ischemia during exercise on a motorized treadmill.Seven New Zealand White rabbits performed a nonischemic controlprotocol and a hindlimb ischemia protocol in which terminal aorticblood flow (ta) was reduced to 51 ± 2% ofpreocclusion ta by partial aortic occlusion after 1.5 min of exercise. Mean arterial pressure (MAP), heart rate, RSNA andta increased in response to exercise and weresimilar between trials during the first 1.5 min of exercise. In thecontrol trial, ta, MAP, and RSNA were stable at anelevated level through an additional 3.5 min of exercise. Hindlimbischemia produced a potent pressor response that plateaued after 2.5 min (+17 ± 4 mmHg, where  designates change). RSNA began toincrease after 1.5 min of ischemic exercise and was significantlyelevated relative to preocclusion RSNA at 2.5 (+25 ± 9%) and3.5 (+47 ± 12%) min of occlusion. These results suggest thatthe muscle chemoreflex can augment sympathoexcitatory drive to thekidney during dynamic exercise.