CIGARETTE-SMOKE, NICOTINE AND CAPSAICIN AEROSOL-INDUCED VASODILATATION IN PIG RESPIRATORY MUCOSA

1. Anaesthetized pigs were used to study vascular responses in the sphenopalatine artery (SPA), superior laryngeal artery (SLA) and bronchial artery (BA) upon exposure to cigarette smoke or aerosol of nicotine and capsaicin. Direct blood flow recordings were made with ultrasonic probes around the vessels. 2. Smoke from one cigarette was administered as inhalation for 2 min with or without a Cambridge filter which removes the particulate matter including nicotine from the smoke. Aerosols of nicotine (2.5 mg) or capsaicin (10 mg) were administered to the nose or the lower airways for 3 min. 3. Cigarette smoke exposure caused a reproducible reduction of the vascular resistance (VR) suggesting vasodilatation in the SPA, SLA and especially the BA. The vasodilatation was not modified by the Cambridge filter, suggesting that it was caused by vapour phase components rather than nicotine. 4. The smoke effect was not changed after pretreatment with the cyclo-oxygenase inhibitor, diclofenac, or with atropine, guanethidine, H1- or H2-histamine receptor antagonists, nedocromil, or by vagotomy. The smoke-evoked decrease in VR was not modified by the nicotinic receptor antagonist chlorisondamine in the SLA or BA. 5. In pigs pretreated with increasing doses of capsaicin two days earlier, the decrease in VR upon smoke exposure in both the BA and SLA was unaffected while the change in VR was attenuated in the SPA. 6. Nicotine aerosol had no effect on VR in the peripheral airways supplied by the BA while a decrease in VR was observed in the SLA and SPA. The nicotine response was reduced after capsaicin pretreatment in the nasal and upper tracheal circulation. 7. Capsaicin aerosol reduced VR in the vascular beds supplied by the SPA, SLA and BA and this response was markedly reduced after capsaicin pretreatment. 8. The mechanisms underlying vasodilatation upon cigarette smoke exposure in the bronchial mucosa are at the moment unclear while both non-cholinergic parasympathetic and sensory components may be involved in the nose. Capsaicin induced a vasodilatation at all levels via sensory mechanisms, whereas nicotine-evoked vasodilatation is restricted to the upper airway mucosa and is at least partly dependent on parasympathetic reflexes involving capsaicin-sensitive sensory nerves.