Mechanisms for reflexive hypertension induced by local application of capsaicin and nicotine to the nasal mucosa

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Abstract
The cardiovascular effects of locally applied nicotine and capsaicin to the nasal mucosa were studied in anesthetized guinea-pigs. Local application of capsaicin (0.3-30 .mu.M) or nicotine (0.3-30 mM) induced dose-dependent increases in arterial blood pressure, mainly due to an increase in perhiperal vascular resistance. The capsaicin and nicotine responses were abolished after local anesthesia and markedly reduced (to .apprx. 20% of control) by combined pretreatment with phentolamine and propranolol, suggesting reflexogenic sympathetic activation. Systemic capsaicin pretreatment abolished the hypertensive effect of capsaicin (30 .mu.M) and reduced the response to nicotine application to .apprx. 25% of control (P < 0.001). Local capsaicin pretreatment of the nasal mucosa 1 wk earlier also significantly reduced the capsaicin response (P < 0.05), while the nicotine-induced increase in blood pressure was not significantly changed. The presence of 2 afferent mechanisms in the nasal mucosa which induce hypertension upon chemical irritation is suggested. The capsaicin response is dependent upon capsaicin-sensitive afferents. The nicotine response involves mainly capsaicin-sensitive neurons and, in addition, a minor component which is resistant to capsaicin pretreatment. The hypertensive effect of nicotine applied locally to the nasal mucosa seems to be mainly mediated via sensory mechanisms other than the sneezing which is not dependent on capsaicin sensitive nerves.