Epicardial application of capsaicin causes tachycardia and pressor effect in guinea pigs

Topical application of picomoles of capsaicin (CAP) to the surface of the left ventricle (epicardial application) of anesthetized guinea pigs evoked dose-dependent increases of heart rate and of mean arterial blood pressure. The pressor responses to epicardial application of CAP were inhibited by systemic administration of pentolinium or a mixture of phentolamine and propranolol whereas only the mixture of phentolamine and propranolol attenuated the tachycardia. The pressor and heart rate responses to epicardial CAP were not modified by acute bilateral vagotomy or prior systemic treatment of animals with atropine, indomethacin, naloxone or a mixture of mepyramine and cimetidine, but both responses were markedly reduced by prior chronic treatment of guinea pigs with CAP or by prior epicardial application of lidocaine. Altogether these results suggest that the pressor effects caused by epicardial application of CAP in anesthetized guinea pigs are reflex in nature and likely to be due to stimulation by CAP of cardiac, sympathetic, CAP-sensitive, sensory nerve endings, whereas the tachycardia caused by epicardial CAP might be mediated by local noradrenaline release (and subsequent cardiac beta adrenoceptor activation) from cardiac, sympathetic, postganglionic nerve fibers and/or terminals.