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Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska 68178-0405
Hyperosmotic saline solutions stimulate
lower airway sensory nerves. To determine whether airway
hyperosmolarity evokes neurally mediated changes in bronchial artery
blood flow (
br), we measured the effect
of injection of small volumes (1 ml) of hyperosmotic saline into a
right lobar bronchus on
br of anesthetized,
artificially ventilated dogs. In 14 dogs, hyperosmotic saline (1,200 and 2,400 mmol/l) increased
br by 58 ± 12 (SE)
and 118 ± 12%, respectively, from a baseline of 8 ± 2 ml/min.
br increased within 6-8 s of the injections,
peaked at 20 s, and returned to control over 2-3 min. Isosmotic
saline had minimal effects. In contrast, hyperosmotic saline decreased
flow in an intercostal artery that did not supply the airways. The
bronchial vasodilation was decreased by 72 ± 11% after combined
blockade of
-adrenoceptors and muscarinic cholinergic receptors and
by 66 ± 6% when the cervical vagus nerves were cooled to 0°C.
Blockade of H1 and H2 histamine receptors did
not reduce the nonvagal response. We conclude that hyperosmolarity of
the lower airways evokes bronchial vasodilation by both a centrally mediated reflex that includes cholinergic and adrenergic efferent pathways and by unidentified local mechanisms.
bronchial artery; hypertonic saline; vagus nerve; autonomic pathways; airway defense reflex; exercise-induced asthma
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