Coronary chemoreflex evoked by intrapericardial nicotine has a somatic component

Area of Science:

• Cardiovascular Physiology
• Neuroscience
• Autonomic Nervous System Regulation

Background:

• Vagally innervated cardiac and pulmonary receptors trigger reflexes affecting blood pressure.
• The pulmonary depressor reflex includes a somatic component that attenuates muscle reflexes.

Purpose of the Study:

• To investigate if the coronary chemoreflex also attenuates somatic reflexes, specifically the knee-jerk reflex.
• To elucidate the neural pathways involved in this potential somatic reflex.

Main Methods:

• Cardiac receptors in anesthetized cats were stimulated using nicotine and bradykinin injected into the pericardial sac.
• The knee-jerk reflex was measured by eliciting it via patellar tendon tapping.
• Vagotomy and procaine blockade were used to determine the neural mediation of observed effects.

Main Results:

• Intrapericardial nicotine significantly attenuated the knee-jerk reflex (-26.2%).
• This attenuation was vagally mediated and dependent on cardiac receptor stimulation.
• Intrapericardial bradykinin augmented the knee-jerk reflex (17.5%), an effect not mediated by vagal nerves.

Conclusions:

• The coronary chemoreflex, a vagally mediated response, includes a somatomotor component that attenuates the knee-jerk reflex.
• This somatic response may play a role in exertional syncope and vasovagal syncope.
• Bradykinin's effect on the knee-jerk reflex is independent of vagal pathways.