Interaction of the chemoreflex and the pulmonary inflation reflex in the regulation of coronary circulation in conscious dogs

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Regulation

Background:

• The control of coronary circulation is complex, involving interactions between reflexes.
• Chemoreflex and pulmonary inflation reflexes play roles in regulating blood flow to the heart.

Purpose of the Study:

• To investigate the interplay between chemoreflex and pulmonary inflation reflex control of coronary circulation.
• To elucidate the mechanisms underlying nicotine-induced coronary vasodilation in conscious dogs.

Main Methods:

• Chemoreflex stimulation using intracarotid nicotine injection in conscious dogs.
• Comparison of responses with spontaneous vs. controlled ventilation.
• Pharmacological blockade of beta-receptors, cholinergic, and alpha-adrenergic systems.
• Assessment of coronary blood flow and resistance.

Main Results:

• Nicotine induced significant coronary vasodilation and decreased coronary resistance, primarily when ventilation was allowed to increase.
• This vasodilation involved a minor vagal component and a major component linked to increased respiratory depth and withdrawal of alpha-adrenergic tone.
• Pulmonary hyperinflation (mechanical or spontaneous) mimicked the major component of nicotine-induced coronary dilation.

Conclusions:

• Nicotine-induced coronary dilation has dual components: a vagal reflex and a more significant pathway involving respiratory changes and alpha-adrenergic tone modulation.
• Pulmonary inflation reflex contributes to coronary vasodilation, potentially through similar efferent pathways as the major component of the chemoreflex.