Am. J. Respir. Crit. Care Med., Vol 153, No. 1, 01 1996, 153-157.
Mechanical ventilation increases substance P concentration in the vagus, sympathetic, and phrenic nerves
E Balzamo, P Joanny, JG Steinberg, C Oliver and Y Jammes
Unite de Recherche 1630 CNRS, Faculte de Medecine Secteur Nord, Marseille, France.
Substance P (SP), a neurotransmitter localized to primary sensory neurons,
is found in the vagus nerve, nodose ganglion, sympathetic chain, and
phrenic nerve in various animal species. However, the changes in
endogeneous SP concentration under various circumstances that involve the
participation of cardiorespiratory afferent nerves are still unexplored. In
the present study, attention was focused on the variations in SP content
measured by radioimmunoassay (RIA) in respiratory afferent nerves (vagus
nerve, cervical sympathetic chain, phrenic nerve) and respiratory muscles
(diaphragm, intercostal muscles) during positive inspiratory pressure (PIP)
breathing alone or PIP with an expiratory threshold load (ETL) in rabbits.
SP was found in all sampled structures in spontaneously breathing control
animals, prevailing in the nodose ganglion. Left-versus right-sided
differences were noticed in nerves. As compared with that in control
animals, the SP concentration was markedly higher in vagal and sympathetic
nervous structures during PIP or PIP with ETL, and also in the phrenic
nerve during ETL breathing. The SP content did not vary in respiratory
muscles. These observations suggest that two very common circumstances of
mechanical ventilation are associated with an increased SP concentration in
nervous structures participating in the control of breathing.
