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Substrate metabolism, hormone interaction, and angiotensin-converting enzyme inhibitors in left ventricular
Y C Zhu1, Y Z Zhu, H Spitznagel
1Department of Pharmacology, Christian Albrechts University of Kiel, Germany.
Insights
Left ventricular hypertrophy impairs heart function and increases ischemia risk. Angiotensin-converting enzyme inhibitors (ACEIs) show promise in preventing cardiac hypertrophy and improving heart metabolism and function.
Area of Science:
- Cardiology
- Molecular Biology
- Physiology
Background:
- Left ventricular hypertrophy (LVH) is a significant risk factor for cardiac ischemia, arrhythmias, and dysfunction.
- Impaired intracellular calcium handling and shifts to fetal-type myofibril isoforms contribute to reduced contractility and relaxation in LVH.
- Severely hypertrophied myocardium faces reduced capillary density, increased diffusion distances, and an anaerobic metabolic state, increasing vulnerability to ischemia.
Purpose of the Study:
- To investigate the mechanisms underlying impaired cardiac function in left ventricular hypertrophy.
- To explore the compensatory and maladaptive responses in hypertrophied and failing myocardium.
- To evaluate the potential benefits of Angiotensin-converting enzyme inhibitors (ACEIs) on cardiac hypertrophy and function.
Main Methods:
- Analysis of intracellular calcium dynamics in hypertrophied myocardium.
- Assessment of myofibril isoform shifts and interstitial fibrosis.
- Evaluation of myocardial metabolic state, including capillary density and enzyme markers.
- Investigation of compensatory mechanisms like atrial natriuretic peptide release and ADP/ATP carrier activation.
- Experimental assessment of ACEIs effects on cardiac hypertrophy, function, and metabolism.
Main Results:
- Slow intracellular calcium movement and fetal-type myofibril isoforms impair myocardial contraction and relaxation.
- Reduced capillary density and anaerobic metabolism in severe LVH increase ischemic vulnerability.
- Compensatory mechanisms (e.g., ANP release) are overwhelmed by vasoconstrictor systems (e.g., renin-angiotensin system).
- ACEIs demonstrate efficacy in preventing cardiac hypertrophy and improving cardiac function and metabolism, potentially via bradykinin potentiation.
Conclusions:
- Left ventricular hypertrophy leads to significant myocardial dysfunction and increased susceptibility to ischemia through various cellular and metabolic alterations.
- While compensatory mechanisms exist, they are often overridden by detrimental neurohumoral factors in advanced stages.
- ACEIs represent a promising therapeutic strategy for mitigating cardiac hypertrophy and enhancing cardiac performance, primarily through bradykinin potentiation.
Abstract:
Left ventricular hypertrophy is considered to be an independent risk factor giving rise to ischemia, arrhythmias, and left ventricular dysfunction. Slow movement of intracellular calcium contributes to the impaired contraction and relaxation function of hypertrophied myocardium. Myofibril content may also be shifted to fetal-type isoforms with decreased contraction and relaxation properties in left ventricular hypertrophy. Myocyte hypertrophy and interstitial fibrosis are regulated independently by mechanical and neurohumoral mechanisms. In severely hypertrophied myocardium, capillary density is reduced, the diffusion distance for oxygen, nutrients, and metabolites is increased, and the ratio of energy-production sites to energy-consumption sites is decreased. The metabolic state of severely hypertrophied myocardium is anaerobic, as indicated by the shift of lactate dehydrogenase marker enzymes. Therefore, the hypertrophied myocardium is more vulnerable to ischemic events. As a compensatory response to severe cardiac hypertrophy and congestive heart failure, the ADP/ATP carrier is activated and atrial natriuretic peptide is released to increase high-energy phosphate production and reduce cardiac energy consumption by vasodilation and sodium and fluid elimination. However, in severely hypertrophied and failing myocardium, vasoconstrictor and sodium- and fluid-retaining factors, such as the renin-angiotensin system, aldosterone, and sympathetic nerve activity, play an overwhelming role. Angiotensin-converting enzyme inhibitors (ACEIs) are able to prevent cardiac hypertrophy and improve cardiac function and metabolism. Under experimental conditions, these beneficial effects can be ascribed mainly to bradykinin potentiation, although a contribution of the ACEI-induced angiotensin II reduction cannot be excluded.