Role of the chemoreceptor in diving bradycardia in rat.

Responses in heart rate and blood pressure to the dive in unanesthetized rats were studied by submersion of the head in water for 30 sec. During the dive, remarkable bradycardia developed and blood pressure was slightly elevated. Bilateral section of the carotid sinus nerves or selective destruction of the carotid body chemoreceptor by intrasinusal injection of acetic acid attenuated the bradycardic response to the dive, while section of the recurrent nerves or section of the sympathetic trunks at the cervical level together with the superior laryngeal nerves had no effect. These data indicate that the chemoreceptor plays an important role in diving bradycardia in rats.