Wengrowski AM, Kuzmiak-Glancy S, Jaimes R 3rd, Kay MW. NADH changes during hypoxia, ischemia, and increased work differ between isolated heart preparations. Am J Physiol Heart Circ Physiol 306: H529 -H537, 2014. First published December 13, 2013; doi:10.1152/ajpheart.00696.2013.-Langendorff-perfused hearts and working hearts are established isolated heart preparation techniques that are advantageous for studying cardiac physiology and function, especially when fluorescence imaging is a key component. However, oxygen and energy requirements vary widely between isolated heart preparations. When energy supply and demand are not in harmony, such as when oxygen is not adequately available, the imbalance is reflected in NADH fluctuations. As such, NADH imaging can provide insight into the metabolic state of tissue. Hearts from New Zealand white rabbits were prepared as mechanically silenced Langendorffperfused hearts, Langendorff-perfused hearts, or biventricular working hearts and subjected to sudden changes in workload, instantaneous global ischemia, and gradual hypoxia while heart rate, aortic pressure, and epicardial NADH fluorescence were monitored. Fast pacing resulted in a dip in NADH upon initiation and a spike in NADH when pacing was terminated in biventricular working hearts only, with the magnitude of the changes greatest at the fastest pacing rate. Working hearts were also most susceptible to changes in oxygen supply; NADH was at half-maximum value when perfusate oxygen was at 67.8 Ϯ 13.7%. Langendorff-perfused and mechanically arrested hearts were the least affected by low oxygen supply, with halfmaximum NADH occurring at 42.5 Ϯ 5.0% and 23.7 Ϯ 4.6% perfusate oxygen, respectively. Although the biventricular working heart preparation can provide a useful representation of mechanical in vivo heart function, it is not without limitations. Understanding the limitations of isolated heart preparations is crucial when studying cardiac function in the context of energy supply and demand.Langendorff; biventricular working; blebbistatin; nadh imaging; workload THE HEART IS RESPONSIBLE FOR pumping blood with vital supplies to the entire body and therefore requires a constant high rate of energy supply. Additionally, the heart has a large dynamic range with the capacity to increase its workload 10-fold and maintain this increase for extended periods of time. This metabolic requirement necessitates acute regulation of energy supply to match demand, as well as a constant adequate oxygen supply. Any limitation in energy supply is rapidly detrimental to cardiac function.The demand for ATP and oxygen varies, depending on the amount of work being performed (12a, 17). The amount of available ATP to the heart at any given time is enough for only a few beats and must constantly be resynthesized to keep up with utilization (16). In the heart, 80 -90% of energy production occurs via oxidative phosphorylation (25). Fats and carbohydrates are broken down and electrons are harvested, reducing NAD ϩ to NADH, (and, to a lesser exte...
Activation of hypothalamic OXT neurons to elevate parasympathetic tone reduced cellular hypertrophy, levels of IL-1β, and fibrosis during TAC-induced HF in rats. Cardiac contractility parameters were significantly higher in TAC + OXT compared with TAC animals. HR sensitivity, but not contractile sensitivity, to β-adrenergic stimulation was improved in TAC + OXT hearts.
Absorbance spectroscopy of intrinsic cardiac chromophores provides nondestructive assessment of cytosolic oxygenation and mitochondria redox state. Isolated perfused heart spectroscopy is usually conducted by collecting reflected light from the heart surface, which represents a combination of surface scattering events and light that traversed portions of the myocardium. Reflectance spectroscopy with complex surface scattering effects in the beating heart leads to difficulty in quantitating chromophore absorbance. In this study, surface scattering was minimized and transmural path length optimized by placing a light source within the left ventricular chamber while monitoring transmurally transmitted light at the epicardial surface. The custom-designed intrachamber light catheter was a flexible coaxial cable (2.42-Fr) terminated with an encapsulated side-firing LED of 1.8 × 0.8 mm, altogether similar in size to a Millar pressure catheter. The LED catheter had minimal impact on aortic flow and heart rate in Langendorff perfusion and did not impact stability of the left ventricule of the working heart. Changes in transmural absorbance spectra were deconvoluted using a library of chromophore reference spectra to quantify the relative contribution of specific chromophores to the changes in measured absorbance. This broad-band spectral deconvolution approach eliminated errors that may result from simple dual-wavelength absorbance intensity. The myoglobin oxygenation level was only 82.2 ± 3.0%, whereas cytochrome and cytochrome + were 13.3 ± 1.4% and 12.6 ± 2.2% reduced, respectively, in the Langendorff-perfused heart. The intracardiac illumination strategy permits transmural optical absorbance spectroscopy in perfused hearts, which provides a noninvasive real-time monitor of cytosolic oxygenation and mitochondria redox state. Here, a novel nondestructive real-time approach for monitoring intrinsic indicators of cardiac metabolism and oxygenation is described using a catheter-based transillumination of the left ventricular free wall together with complete spectral analysis of transmitted light. This approach is a significant improvement in the quality of cardiac optical absorbance spectroscopic metabolic analyses.
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