Respiratory and circulatory reflexes induced by nicotine injections: role of carotid body chemoreceptors.

Intravenous and intracarotid injections of nicotine were delivered to cats anesthetized with pentobarbital. Low doses of nicotine were found to induce reflex hyperventilation and hypertension, mainly due to excitation of carotid body chemoreceptors. The frequency of discharge of carotid nerve chemosensory fibres was increased by nicotine in doses as low as 1 mug/kg when injected intravenously and 50 ng when injected into the carotid artery. Nicotine also activates vagal afferent fibres; some of them produce reflex excitation of the respiratory and vasomotor centres, but others provoke reflex inhibition. High doses of nicotine can act directly upon the medulla provoking acceleration or arrest of ventilation. Nicotine can also induce 'late' changes of b.p. (delay 5 sec or more) which are not mediated by the carotid or vagus nerves.