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In vivo detection of endogenous acetylcholine release in cat ventricles
T Akiyama1, T Yamazaki, I Ninomiya
1Department of Cardiac Physiology, National Cardiovascular Center Research Institute, Osaka, Japan.
Insights
This study used in vivo heart dialysis in cats to measure acetylcholine (ACh) release. Vagal nerve stimulation significantly increased ACh levels, demonstrating a method to monitor cardiac vagal activity.
Area of Science:
- Cardiovascular Physiology
- Neuropharmacology
- Analytical Chemistry
Background:
- Endogenous acetylcholine (ACh) plays a crucial role in cardiac function.
- Accurate measurement of ACh release in the in vivo heart is essential for understanding cardiac autonomic regulation.
- Existing methods may not fully capture dynamic ACh release in the beating heart.
Purpose of the Study:
- To develop and validate a microdialysis technique for detecting and monitoring endogenous acetylcholine release in the in vivo feline heart.
- To investigate the relationship between vagal nerve stimulation and ACh release in the left ventricular myocardium.
- To assess the impact of ganglionic blockade on vagally-mediated ACh release.
Main Methods:
- Application of in vivo cardiac microdialysis in anesthetized cats.
- Implantation of dialysis probes into the left ventricular myocardium.
- Perfusion of probes with Krebs-Henseleit solution containing eserine and measurement of dialysate ACh via high-performance liquid chromatography.
- Electrical stimulation of efferent vagal nerves at varying frequencies and assessment of ganglionic blocker effects.
Main Results:
- Vagal nerve stimulation (10 Hz) caused a significant increase in dialysate ACh concentration (from 596 ± 118 pM to 12,210 ± 1,661 pM).
- Intravenous administration of hexamethonium (a ganglionic blocker) abolished the vagal stimulation-induced ACh increase, while local perfusion had no effect.
- ACh release showed a frequency-dependent increase with vagal nerve stimulation (2 Hz, 5 Hz, and 10 Hz).
Conclusions:
- The microdialysis technique effectively detects and monitors endogenous ACh release from postganglionic vagal nerves in the in vivo heart.
- This method allows for the estimation of relative changes in efferent cardiac vagal nerve activity.
- The findings support the role of ACh in vagal modulation of cardiac function and provide a tool for further research.
Abstract:
To detect and monitor endogenous acetylcholine (ACh) release in the in vivo heart, we applied a dialysis technique to the hearts of anesthetized cats. Dialysis probes were implanted in the left ventricular myocardium and were perfused with Krebs-Henseleit solution containing Eserine (10(-4) M) at 3 microliters/min. Dialysate ACh concentration was measured with high-performance liquid chromatography. In four cats, the response to vagal stimulation was studied. Electrical stimulation of efferent vagal nerves (10 Hz) significantly increased dialysate ACh concentration from 596 +/- 118 (control) to 12,210 +/- 1,661 pM. After stimulation, dialysate ACh concentration significantly decreased to 382 +/- 80 pM below control. The influence of ganglionic blocker was determined in six cats. Control vagal nerve stimulation (10 Hz) increased dialysate ACh concentration from 582 +/- 136 to 9,102 +/- 754 pM. Local perfusion of hexamethonium (10(-4) M) did not affect this nerve stimulation-induced ACh increase (8,611 +/- 1,189 pM), and intravenous administration of hexamethonium (20 mg/kg) prevented this increase (340 +/- 88 pM). We examined the response to vagal nerve stimulation at different frequencies in three cats. Vagal nerve stimulation increased dialysate ACh concentration from a control of 588 +/- 211 to 1,227 +/- 195 pM at 2 Hz, 3,946 +/- 1,059 pM at 5 Hz, and 9,366 +/- 1,873 pM at 10 Hz. Dialysate ACh concentration reflects ACh release from postganglionic vagal nerves innervating the left ventricular myocardium; the dialysis technique permits estimation of relative changes in efferent cardiac vagal nerve activity.