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Cardiac sympathetic afferent reflex in dogs with congestive heart failure
1Department of Physiology and Biophysics, University of Nebraska College of Medicine, Omaha 68198-4575, USA.
Insights
In heart failure (HF), the cardiac sympathetic afferent reflex is enhanced, contributing to increased sympathetic outflow. This heightened reflex may be linked to prostaglandin synthesis and increased sympathetic tone in chronic HF.
Area of Science:
- Cardiovascular Physiology
- Neuroscience
Background:
- Sympathetic tone is elevated in chronic heart failure (HF).
- The cardiac sympathetic afferent reflex is a known sympathoexcitatory reflex.
- The role of this reflex in controlling sympathetic outflow during HF has not been studied.
Purpose of the Study:
- To test the hypothesis that cardiac sympathetic afferent reflexes are enhanced in HF.
- To determine if these enhanced reflexes contribute to increased sympathetic outflow in HF.
Main Methods:
- Created a canine model of chronic heart failure (HF) using ventricular pacing.
- Measured hemodynamic (arterial pressure, heart rate) and renal sympathetic nerve activity (RSNA) responses to epicardial bradykinin and capsaicin in HF and sham dogs.
- Utilized sinoaortic denervation and vagotomy to isolate cardiac reflexes.
- Administered indomethacin (a cyclooxygenase blocker) and topical lidocaine to assess mechanisms.
Main Results:
- HF dogs showed significantly greater increases in arterial pressure, RSNA, and heart rate in response to bradykinin compared to sham dogs.
- RSNA response to capsaicin was also significantly increased in HF dogs.
- Indomethacin attenuated the reflex responses to bradykinin in HF dogs, suggesting prostaglandin involvement.
- Lidocaine blockade of cardiac sympathetic afferents reduced baseline RSNA more in HF dogs than in sham dogs.
Conclusions:
- The cardiac sympathetic afferent reflex is sensitized in the chronic heart failure state.
- Enhanced prostaglandin synthesis may mediate the increased reflex response to bradykinin in HF.
- This sensitized cardiac sympathetic afferent reflex likely contributes to the sustained elevation of sympathetic tone observed in chronic heart failure.
Abstract:
It is well accepted that sympathetic tone is elevated in chronic heart failure (HF) and that the cardiac sympathetic afferent reflex is a sympathoexcitatory reflex. There have been no studies designed to examine the role of this reflex in control of sympathetic outflow in the HF state. In this study we tested the hypothesis that cardiac sympathetic afferent reflexes are enhanced in HF and are, therefore, capable of contributing to the increase in sympathetic outflow in this disease state. Ventricular pacing was carried out in 14 dogs until signs of HF were evident. Fourteen sham dogs served as controls. At the time of the acute experiment the dogs were anesthetized with alpha-chloralose. The hemodynamic [arterial pressure and heart rate (HR)] and renal sympathetic nerve activity (RSNA) responses to left ventricular epicardial application of two doses of bradykinin (BK) and capsaicin (Cap) were determined in the sinoaortic-denervated and vagotomized state. The MAP, RSNA, and HR responses to BK were greater in the HF group compared with the sham group. The RSNA response to BK (50 micrograms) in the HF group was significantly increased (34.0 +/- 5.9 vs. 11.5 +/- 4.2%, P < 0.05). The MAP, RSNA, and HR responses to Cap in the HF group were similar to the responses to BK. The RSNA response to Cap in the HF group was significantly increased (29.8 +/- 11.3 vs. 13.8 +/- 2.3% for 10 micrograms, P < 0.05 and 46.5 +/- 10.7 vs. 18.7 +/- 3.1% for 100 micrograms, P < 0.05). The cyclooxygenase blocker indomethacin (5 mg/kg i.v.) attenuated the reflex responses to BK in the HF group. These data suggest that the enhanced cardiac sympathetic afferent reflex to epicardial BK in HF appears to be mediated by altered levels of prostaglandin synthesis. Blockade of cardiac sympathetic afferents with topical lidocaine reduced baseline of RSNA significantly more in the HF state than in the normal state (-24.2 +/- 3.6 vs. -4.3 +/- 4.5%, P < 0.05). We conclude from these data that the cardiac sympathetic afferent reflex is sensitized in the HF state and speculate that this enhanced cardiac sympathetic afferent reflex may contribute to the sustained higher sympathetic tone in chronic HF.