Responses of laryngeal capsaicin-sensitive receptors to volatile anesthetics in anesthetized dogs.

The responses of laryngeal capsaicin (CAPS)-sensitive receptors to halothane, enflurane, isoflurane and sevoflurane were evaluated in anesthetized spontaneously breathing dogs from the afferent activity of the internal branch of the superior laryngeal nerve. The CAPS-sensitive receptors were clearly distinguished from irritant receptors by their responsiveness to CAPS and their lack of responsiveness to water. All the CAPS-sensitive receptors were significantly stimulated by all volatile anesthetics in a concentration-related manner, and the activation by halothane, enflurane, and isoflurane was significantly greater than by sevoflurane. In contrast, responses of irritant receptors to the volatile anesthetics were divided into three types (stimulation, inhibition or non-response), and did not differ among anesthetics. In conclusion, the present study demonstrated that the CAPS-sensitive receptors were consistently stimulated by halogenated volatile anesthetics and especially by halothane, enflurane, and isoflurane, and that these responses were dissimilar to the variable responses of irritant receptors.