CEREBRAL NORADRENALINE SPILLOVER AND ITS RELATION TO MUSCLE SYMPATHETIC NERVOUS ACTIVITY IN HEALTHY-HUMAN SUBJECTS

Studies using internal jugular vein blood sampling in human subjects h ave demonstrated the release of noradrenaline from the brain and have provided a link between central nervous system noradrenergic neuronal activity and renal, cardiac and total body sympathetic activity, The a im of this study was to further categorise the dependence of regional sympathetic nervous function on central nervous system noradrenergic n euronal processes by combining measures of internal jugular venous nor adrenaline spillover, as an indicator of brain noradrenaline release, and cerebral blood flow scans with measures of the overall integrated neuronal firing rate for the body as a whole, the spillover of noradre naline into the coronary sinus and with measurements of resting muscle sympathetic nerve activity. Positive veno-arterial plasma noradrenali ne gradients were found across the brain, with the plasma concentratio n being 17 +/- 3% (p < 0.01) greater in the internal jugular vein. Lin ear regression analysis revealed a significant relationship between th e degree of muscle sympathetic nerve activity and the spillover of nor adrenaline from subcortical brain regions (y = 0.1x + 16.0; r = 0.81, p < 0.02). The rate of spillover of noradrenaline for the body as a wh ole also bore a significant association with the rate of subcortical n oradrenaline spillover (y = 0.01x + 2.33; r = 0.71, p < 0.05). Cortica l noradrenaline spillover was not related to any of the sympathetic ne rvous system parameters measured in this study. The demonstration of a direct relationship between the rate of peroneal nerve firing and the spillover of noradrenaline from subcortical brain regions provides fu rther support for the concept of central nervous system noradrenergic cell groups behaving in a sympathoexcitatory role.