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Influence of reduced presynaptic myocardial norepinephrine stores on left ventricular contractility
1First Department of Internal Medicine, Tohoku University School of Medicine, Miyagi, Japan.
Insights
Decreased myocardial norepinephrine, a hallmark of heart failure, impairs left ventricular contractility. This study shows that lowering norepinephrine levels directly reduces cardiac muscle contraction, suggesting a causal link.
Area of Science:
- Cardiology
- Neuroscience
- Physiology
Background:
- Myocardial norepinephrine levels are reduced in congestive heart failure.
- The direct impact of this norepinephrine depletion on myocardial contraction remains unstudied.
Purpose of the Study:
- To determine if decreased myocardial norepinephrine itself negatively affects left ventricular contractility.
- To investigate the role of norepinephrine in regulating cardiac contractility during sympathetic stimulation.
Main Methods:
- Left ventricular contractility was assessed in control and reserpinized dogs via left stellate ganglion stimulation.
- Key indicators of contractility included left ventricular max dp/dt and pressure-segment length relationships.
- Myocardial norepinephrine content was measured before and after stimulation.
Main Results:
- Reserpinized dogs showed significant decreases in left ventricular max dp/dt and pressure-segment length slope after stimulation.
- Control dogs exhibited no significant changes in contractility parameters.
- Norepinephrine levels were substantially lower in reserpinized dogs and decreased further post-stimulation.
Conclusions:
- Reduced myocardial norepinephrine levels are directly responsible for impaired left ventricular contractility.
- This finding provides a mechanistic link between norepinephrine depletion and contractile dysfunction in heart failure.
- Targeting norepinephrine levels may be a therapeutic strategy for heart failure.
Abstract:
Many investigators have reported that myocardial norepinephrine content is decreased in congestive heart failure. However there have been no studies of how decrease in myocardial norepinephrine might influence myocardial contraction. To clarify whether decreased myocardial norepinephrine per se affects myocardial contraction, we observed the change in left ventricular contractility during 30 min of left stellate ganglion stimulation in control and acutely reserpinized dogs. We obtained left ventricular max dp/dt and left ventricular end-systolic pressure-segment length relationships as indicators of left ventricular contractility. Both parameters decreased after left stellate ganglion stimulation in reserpinized dogs (left ventricular max dp/dt: 2064 +/- 200 to 1608 +/- 168 mmHg/s, left ventricular end-systolic pressure-segment length slope 117 +/- 22 to 79 +/- 14 mmHg/mm, n = 8, P less than 0.05), while they did not change in controls. In reserpinized dogs, left ventricular norepinephrine content decreased to one-third that of controls before the stimulation, and further decreased after stimulation. These data indicate that lowered myocardial norepinephrine itself may be responsible for the negative effect on left ventricular contractility in congestive heart failure.