Muscle Sympathetic Nerve Activity Averaged Over 1 Minute Parallels Renal and Cardiac Sympathetic Nerve Activity in Response to a Forced Baroreceptor Pressure Change

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Abstract
Background— Despite the accumulated knowledge of human muscle sympathetic nerve activity (SNA) as measured by microneurography, whether muscle SNA parallels renal and cardiac SNAs remains unknown. Method and Results— In experiment 1, muscle (microneurography, tibial nerve), renal, and cardiac SNAs were recorded in anesthetized rabbits (n=6) while arterial pressure was changed by intravenous bolus injections of nitroprusside (3 μg/kg) followed by phenylephrine (3 μg/kg). In experiment 2, the carotid sinus region was vascularly isolated in anesthetized, vagotomized, and aorta-denervated rabbits (n=10). The 3 SNAs were recorded while intracarotid sinus pressure was increased stepwise from 40 to 160 mm Hg in 20-mm Hg increments maintained for 60 seconds each. Muscle SNA averaged over 1 minute was well correlated with renal (r=0.96±0.01, mean±SE) and cardiac (r=0.96±0.01) SNAs in experiment 1 (baroreflex closed-loop condition) and also with renal (r=0.97±0.01) and cardiac (r=0.97±0.01) SNAs in experiment 2 (ba...