Muscle sympathetic nerve activity averaged over 1 minute parallels renal and cardiac sympathetic nerve activity in response to a forced baroreceptor pressure change

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 (baroreflex open-loop condition). Conclusions - Muscle SNA averaged over 1 minute parallels renal and cardiac SNAs in response to a forced baroreceptor pressure change.