Differential control of sympathetic nerve activity and hypertension

Abstract

Once thought to respond uniformly to stimuli (the “fight or flight” effect), the sympathetic nervous system is now considered to be able to exhibit differential control of sympathetic outflow. One emerging hypothesis is that cardiovascular diseases provoke or are exacerbated by selective changes in sympathetic nerve activity (SNA) to specific organs e.g. the kidney. Before this possibility can be considered, we have to assess the ability of different stimuli to provoke selective changes in regional SNA. We explore the possibility that renal SNA and vasomotor SNA in the conscious rabbit are differentially regulated using a range of stimuli including volume expansion, hypoxia and baroreflex activation. We measured SNA to the kidney and the hind limb vasculature (lumbar SNA) in 7 conscious rabbits 6–8 days after the implantation of recording electrodes. Volume expansion (1.5ml/kg/min) resulted in a significant decrease in renal SNA to 66 ± 7% of control levels but no change in lumbar SNA (127 ± 20%). Neither hypoxia (10% O2 and 3% CO2) nor baroreflex curves showed any differential response of renal and lumbar SNA. These results indicate differential control of renal and lumbar SNA in response to acute stimuli and highlight the importance of using a range of stimuli when investigating sympathetic outflow to different regions. Supported by the Health Research Council of New Zealand and Auckland Medical Research Foundation.