Veratrine-induced reflexes and cough.

Area of Science:

• Cardiovascular Physiology
• Respiratory Physiology
• Neuropharmacology

Background:

• Cough is a vital protective reflex, but its excessive activation can be detrimental.
• Veratrine alkaloids are known to stimulate sensory receptors, influencing cardiovascular and respiratory functions.
• Understanding the interplay between veratrine-induced reflexes and the cough reflex is crucial for managing respiratory conditions.

Purpose of the Study:

• To investigate the effect of veratrine-induced reflexes on the intensity of the cough reflex in anesthetized cats.
• To determine the mechanisms underlying the interaction between veratrine and cough, particularly the role of cardiac receptors and medullary respiratory neurons.

Main Methods:

• Anesthetized cats (sodium pentobarbital) were used to study cough reflexes.
• Cough was elicited via mechanical stimulation of the tracheobronchial mucosa.
• Veratrine was administered intravenously and intracardially, and its effects on blood pressure, heart rate, respiratory rate, tidal volume, and cough intensity (measured by esophageal pressure changes) were recorded.

Main Results:

• Intravenous veratrine induced apnea, bradycardia, and hypotension, significantly decreasing cough intensity during apnea.
• Cough intensity remained unchanged when mechanical stimulation was repeated during post-apneic breathing with residual hypotension.
• Intracardial veratrine also caused bradycardia, hypotension, and reduced respiratory rate/tidal volume, with a significant decrease in immediate post-injection cough intensity.

Conclusions:

• Veratrine-induced reflexes, likely originating from cardiac receptors, depress the cough reflex.
• The observed inhibition of cough is potentially mediated indirectly through the suppression of medullary respiratory neurons.
• These findings suggest a neuro-cardiac pathway influencing the cough reflex, with implications for pharmacological interventions.