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Afferent pathways of reflex hypotension and bradycardia during coronary occlusion
Insights
This study reveals that the right-sided vagal nerves are crucial for triggering reflex hypotension and bradycardia during coronary occlusion (CO). Blocking these nerves significantly reduces these cardiovascular responses in cats.
Area of Science:
- Cardiovascular Physiology
- Neuroscience
Background:
- Coronary occlusion (CO) elicits protective reflex responses, including hypotension and bradycardia.
- The specific neural afferent pathways involved in these reflexes are not fully elucidated.
Purpose of the Study:
- To determine the neural afferent pathways mediating reflex hypotension and bradycardia during coronary occlusion (CO) in anesthetized cats.
- To investigate the role of vagal afferent activity in these responses.
Main Methods:
- Induction of CO via occlusion of the left anterior descending (LAD) or circumflex coronary artery (Cx).
- Vagal cold blockade (bilateral, right, or left) to assess the contribution of different vagal pathways.
- Section of specific cardiac nerves on the right side (pericoronary, vagal cardiac nerve trunk, caudal vagal cardiac nerves).
- Electrical stimulation and recording of afferent nerve activity during CO.
Main Results:
- Coronary occlusion (CO) induced significant hypotension and bradycardia.
- Bilateral vagal blockade (BVB) most effectively attenuated these responses, followed by right vagal blockade (RVB) and then left vagal blockade (LVB).
- Section of right-sided cardiac nerves significantly reduced the circulatory responses to CO.
- Electrical stimulation and recording confirmed increased afferent activity in these nerves during CO.
Conclusions:
- Vagal afferent pathways, predominantly on the right side, play a critical role in mediating reflex hypotension and bradycardia during coronary occlusion (CO).
- Specific cardiac nerves transmit this crucial afferent information, highlighting their importance in cardiovascular reflex regulation.
Abstract:
Neural afferent pathways mediating reflex hypotension and bradycardia during coronary occlusion (CO) were determined mainly on the right side in anesthetized cats. Brief occlusion of the left anterior descending (LAD) or circumflex coronary artery (Cx) reuslted in significant hypotension and bradycardia, both of which could be attenuated by bilateral (BVB), unilateral right (RVB), or left vagal cold blockade (LVB) in the nec. The degree of attenuation in the responses was greater as follows: BVB greater than RVB greater than LVB for LAD occlusion, and BVB greater than RBV = LBV for Cx occlusion. Randomized section of cardiac nerves, i.e., the pericoronary nerve, vagal cardiac nerve trunk, and caudal vagal cardiac nerves on the right side produced significant attenuations in the circulatory responses to CO. These results indicate that vagal afferent activity transmitted via these cardiac nerves plays an important role in mediating the reflex responses to CO. This conclusion was further substantiated by electrical stimulation of afferent fibers in thee nerves or by recording increased afferent spontaneous activity form them during CO.