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A C T A M E D I C A M A R T I N I A N A 2 0 0 5 5/2 17
STIMULATION OF DISTAL ESOPHAGUS HAS NO INFLUENCE ON THE
COUGH REFLEX IN AWAKE GUINEA PIGS WITH EXPERIMENTAL
ALLERGIC RHINITIS
JANA PLEVKOVÁ, MARIANA BROZMANOVÁ, SILVIA VARECHOVÁ, MILOŠ TATÁR
Department of Pathophysiology, Comenius University, Jessenius Faculty of Medicine in Martin, Slovakia
A b s t r a c t
Intranasal stimulation with capsaicin and experimentally induced rhinitis enhances cough response probably via
central plasticity of the nucleus of the solitary tract neurons due to strong afferent inputs from the nose (1). Isolated
intraesophageal administration of capsaicin did not induce any changes in the cough response (2).
This study was designed to test whether combinations of afferent inputs from the nose and esophagus could enhance
the intensity of citric acid (CA) induced cough in guinea pigs.
16 male TRIK strain guinea pigs were sensitised by ovalbumin. 21 days after sensitization was confirmed by skin
tests. Experimental allergic rhinitis was induced in these animals by intranasal ovalbumin challenge. After development
of nasal symptoms the animals of experimental group (E) were challenges with intraesophageal (IE) capsaicin (1000 μM,
250 μl). Controls received IE saline. Cough was induced during IE stimulation both in E and C groups by citric acid and
compared to baseline cough response tested in the beginning of the study. Number of coughs was analysed from pneumotachographic
records of airflow changes typical for cough.
The number of CA induced coughs in C was increased after the induction of rhinitis and IE administration of saline
[4 (1.5-5) vs 6 (3.5-8), p < 0.05]. Similar result was obtained for group of E animals with rhinitis IE challenged with capsaicin
[3(2-4) vs 5 (5-6.5), p < 0.05]. This increase of the number of coughs is due to rhinitis. We did not find any differences
in the cough response that could be ascribed to IE administration of saline or capsaicin (p = 0.26).
Conclusion: Intraesophageal administration of capsaicin did not affect CA induced cough in guinea pigs suffering
from allergic rhinitis.
K e y w o r d s : cough plasticity, allergic rhinitis, intraesophageal capsaicin challenge, guinea pig cough models
INTRODUCTION
In 1977, Irwin and coworkers (3) published a comprehensive review proposing that the cause
of cough could be determined if a systematic evaluation was performed of the anatomic locations
where cough receptors reside in the afferent limb of the cough reflex. The afferent limb includes
the vagus nerve, which also innervates the esophagus. Using this protocol, Irwin and coworkers
(3) reported a prospective trial in which the cause of cough was found in all subjects and specific
therapy toward the cause resulted in cough resolution in 98% of subjects. Gastroesophageal
reflux was the etiology of cough in 10% of their population when the diagnosis was made by history,
endoscopy, or barium esophagogram (4).
The utility of the anatomic diagnostic protocol for chronic persistent cough and the importance
of GERD as a cause of cough is proved (5, 6, 7).
There are two proposed mechanisms of GERD-associated cough: (A) acid in the distal esophagus
stimulating an esophageal-tracheobronchial cough reflex, and (B) microaspiration or
macroaspiration of esophageal contents into the larynx and tracheobronchial tree. A number of
studies have been done to examine potential mechanisms affecting cough reflex in patients suffering
from pathological gastroesophageal reflux (8, 9, 10).
In addition to the discussed points of pathogenesis of chronic cough in patients with GERD,
there may be at least one important mechanism involved. It is supposed that activity of central
cough pattern generator (CPG) is under plasticity of numerous stimuli, conducted to the brainstem
via afferent nerve connections of these afferents with neuronal circuits (network) responsible
for cough. Afferent stimuli originated in the nasal mucosa in patients suffering from rhinitis
Address for correspondence:
Jana Plevková MD, PhD,Department of Pathophysiology,
Jessenius Faculty of Medicine, Commenius University, Sklabinska str. 26, 037 53 MARTIN,
Phone: 4238 213, 0904 828 142, e-mail: plevkova@jfmed.uniba.sk