title: Single-unit muscle sympathetic nervous activity and its relation to cardiac noradrenaline spillover.
abstract: Recent work using single-unit sympathetic nerve recording techniques has demonstrated aberrations in the firing pattern of sympathetic nerves in a variety of patient groups. We sought to examine whether nerve firing pattern is associated with increased noradrenaline release. Using single-unit muscle sympathetic nerve recording techniques coupled with direct cardiac catheterisation and noradrenaline isotope dilution methodology we examined the relationship between single-unit firing patterns and cardiac and whole body noradrenaline spillover to plasma. Participants comprised patients with hypertension (n=6), depression (n=7) and panic disorder (n =9) who were drawn from our ongoing studies. The patient groups examined did not differ in their single-unit muscle sympathetic nerve firing characteristics nor in the rate of spillover of noradrenaline to plasma from the heart. The median incidence of multiple spikes per beat was 9%. Patients were stratified according to the firing pattern: low level of incidence (less than 9% incidence of multiple spikes per beat) and high level of incidence (greater than 9% incidence of multiple spikes per beat). High incidence of multiple spikes within a cardiac cycle was associated with higher firing rates (P <0.0001) and increased probability of firing (P <0.0001). Whole body noradrenaline spillover to plasma and (multi-unit) muscle sympathetic nerve activity in subjects with low incidence of multiple spikes was not different to that of those with high incidence of multiple spikes. In those with high incidence of multiple spikes there occurred a parallel activation of the sympathetic outflow to the heart, with cardiac noradrenaline spillover to plasma being two times that of subjects with low nerve firing rates (11.0 ± 1.5 vs. 22.0 ± 4.5 ng min⁻¹, P <0.05). This study indicates that multiple within-burst firing and increased single-unit firing rates of the sympathetic outflow to the skeletal muscle vasculature is associated with high cardiac noradrenaline spillover.
authors.affiliation: Human Neurotransmitters Laboratory, Baker IDI Heart & Diabetes Institute, PO Box 6492 St Kilda Road Central, Melbourne, Vic 8008, Australia. elisabeth.lambert@bakeridi.edu.au
authors.forename: Elisabeth A
authors.initials: EA
authors.lastname: Lambert
authors.forename: Markus P
authors.initials: MP
authors.lastname: Schlaich
authors.forename: Tye
authors.initials: T
authors.lastname: Dawood
authors.forename: Carolina
authors.initials: C
authors.lastname: Sari
authors.forename: Reena
authors.initials: R
authors.lastname: Chopra
authors.forename: David A
authors.initials: DA
authors.lastname: Barton
authors.forename: David M
authors.initials: DM
authors.lastname: Kaye
authors.forename: Mikael
authors.initials: M
authors.lastname: Elam
authors.forename: Murray D
authors.initials: MD
authors.lastname: Esler
authors.forename: Gavin W
authors.initials: GW
authors.lastname: Lambert
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D003863:Depression / Q000503:physiopathology; D005260:Female; D006321:Heart / Q000294:innervation / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D032383:Myocytes, Cardiac / Q000502:physiology*; D009638:Norepinephrine / Q000097:blood / Q000502:physiology*; D016584:Panic Disorder / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000502:physiology*
chemical_list: D009638:Norepinephrine