Veratrine-induced reflexes and cough

With cats anaesthetized with sodium pentobarbital we studied how veratrine-induced reflexes interact with cough. Cough was elicited by mechanical stimulation of tracheobronchial mucosa and its intensity was evaluated from the changes in oesophageal pressure. Veratrine injected intravenously produced apnoea, bradycardia and long-lasting hypotension. With each dose the intensity of cough was significantly decreased during the apnoea. When the mechanical stimulus was repeated during the breathing following apnoea with remaining hypotension, cough intensity parameters were not changed from control. Veratrine injected intracardially caused bradycardia, hypotension, and decreases in respiratory rate and tidal volume. The intensity of cough elicited just after injection of veratrine was also significantly decreased. We suggest that veratrine-induced reflexes depress the cough reflex mainly by inhibitory reflexes arising from cardiac receptors. The inhibition of cough is probably mediated indirectly via the inhibition of medullary respiratory neurons.