Recently, we have shown that chronic exercise increases endothelium-derived relaxing factor (EDRF)/nitric oxide (NO)-mediated epicardial coronary artery dilation in response to brief occlusion and acetylcholine. This finding suggests that exercise can provide a stimulus for the enhanced production of EDRF/NO, thus possibly contributing to the beneficial effects of exercise on the cardiovascular system. Therefore, the purpose of the present study was to examine whether chronic exercise could influence the production of NO (measured as the stable degradation product, nitrite) and endothelial cell NO synthase (ECNOS) gene expression in vessels from dogs after chronic exercise. To this end, dogs were exercised by running on a treadmill (9.5 km/h for 1 hour, twice daily) for 10 days, and nitrite production in large coronary vessels and microvessels and ECNOS gene expression in aortic endothelial extracts were assessed. Acetylcholine (10`to mol/L) dose-dependently increased the release of nitrite (inhibited by nitro-L-arginine) from coronary arteries and microvessels in control and exercised dogs. Moreover, acetylcholine-stimulated nitrite production was markedly enhanced in large coronary arteries and microvessels prepared from hearts E a ndothelium-derived relaxing factor (EDRF), identified as nitric oxide (NO)12 or a closely related molecule,3 is released by the endothelium in response to local hormones, changes in blood flow velocity, or endothelial shear stress.4 However, the physiologically relevant stimulus for EDRF/NO release in vivo is not known and may reflect the summation of local hormones and blood flow. Evidence supporting the contribution of basally released EDRF/NO to the regulation of vascular tone is derived from experiments showing that specific inhibitors of NO synthase (NOS) elicit a prolonged pressor response and reduce regional blood flows in vivo and inhibit endothelium-dependent relaxations in vitro.5

The purpose of this study was to determine whether the heart in large mammals contains cardiac progenitor cells that regulate organ homeostasis and regenerate dead myocardium after infarction. We report that the dog heart possesses a cardiac stem cell pool characterized by undifferentiated cells that are self-renewing, clonogenic, and multipotent. These clonogenic cells and early committed progeny possess a hepatocyte growth factor (HGF)-cMet and an insulin-like growth factor 1 (IGF-1)-IGF-1 receptor system that can be activated to induce their migration, proliferation, and survival. Therefore, myocardial infarction was induced in chronically instrumented dogs implanted with sonomicrometric crystals in the region of the left ventricular wall supplied by the occluded left anterior descending coronary artery. After infarction, HGF and IGF-1 were injected intramyocardially to stimulate resident cardiac progenitor cells. This intervention led to the formation of myocytes and coronary vessels within the infarct. Newly generated myocytes expressed nuclear and cytoplasmic proteins specific of cardiomyocytes: MEF2C was detected in the nucleus, whereas ␣-sarcomeric actin, cardiac myosin heavy chain, troponin I, and ␣-actinin were identified in the cytoplasm. Connexin 43 and N-cadherin were also present. Myocardial reconstitution resulted in a marked recovery of contractile performance of the infarcted heart. In conclusion, the activation of resident primitive cells in the damaged dog heart can promote a significant restoration of dead tissue, which is paralleled by a progressive improvement in cardiac function. These results suggest that strategies capable of activating the growth reserve of the myocardium may be important in cardiac repair after ischemic injury.cardiac stem cells ͉ myocardial infarction ͉ myocardial regeneration

To determine the effects of loading on active and passive tensions, programmed cell death, superoxide anion formation, the expression of Fas on myocytes, and side-to-side slippage of myocytes, papillary muscles were exposed to 7-8 and 50 mN/mm2 and these parameters were measured over a 3-h period. Overstretching produced a 21-and a 2.4-fold increase in apoptotic myocyte and nonmyocyte cell death, respectively. Concurrently, the generation of reactive oxygen species increased 2.4-fold and the number of myocytes labeled by Fas protein 21-fold. Moreover, a 15% decrease in the number of myocytes included in the thickness of the papillary muscle was found in combination with a 7% decrease in sarcomere length and the inability of muscles to maintain stable levels of passive and active tensions. The addition of the NO-releasing drug, C87-3754, prevented superoxide anion formation, programmed cell death, and the alterations in active and passive tensions with time of overloaded papillary muscles. In conclusion, overstretching appears to be coupled with oxidant stress, expression of Fas, programmed cell death, architectural rearrangement of myocytes, and impairment in force development of the myocardium. (J. Clin. Invest. 1995. 96:2247-2259

Abstract-The aim of the present study was to determine whether cardiac nitric oxide (NO) production changes during the progression of pacing-induced heart failure and whether this occurs in association with alterations in myocardial metabolism. Dogs (nϭ8) were instrumented and the heart paced until left ventricular end-diastolic pressure reached 25 mm Hg and clinical signs of severe failure were evident. Every week, hemodynamic measurements were recorded and blood samples were withdrawn from the aorta and the coronary sinus for measurement of NO metabolites, O 2 content, free fatty acids (FFAs), and lactate and glucose concentrations. ne of the proposed mechanisms of cardiac dysfunction in heart failure attributes a major role to an excessive production of nitric oxide (NO) in the heart and, specifically, in myocytes.1,2 Circulating proinflammatory cytokines, found in high concentrations in plasma of patients with heart failure, 3 would stimulate the expression of inducible NO synthase (iNOS) with consequent overproduction of NO. NO has, among other functions, negative inotropic effects at high concentrations, as demonstrated in vitro.4-6 A similar mechanism of cardiac depression has been recognized previously in septic shock, although the levels of circulating cytokines and NO catabolites in this syndrome are much higher than those found during heart failure. 3,[7][8][9] However, to date, evidence of an increase in cardiac production of NO, sufficient to cause a negative inotropic action during heart failure, has not been provided. The finding that iNOS is expressed in tissue from failing hearts does not necessarily imply that cardiomyocytes are exposed to toxic concentrations of NO. Indeed, it is the amount of NO and not the enzyme isotype generating it that determines the degree to which cardiac function would be depressed. Numerous studies suggest that NO release is rather low in heart failure. In clinical and animal studies, 2,10 pharmacological blockade of NO synthases (NOS) did not alter baseline hemodynamics, indicating that, rather than being characterized by overproduction, systemic NO synthesis could already be minimal. Several investigations, including our own, in patients and in animal models of heart failure report an impairment of endothelial release of NO in large arteries and in coronary microvessels.11-14 The reduced vascular NO

Background-The nuclear receptors peroxisome proliferator-activated receptor-␣ (PPAR␣) and retinoid X receptor ␣ (RXR␣) stimulate the expression of key enzymes of free fatty acid (FFA) oxidation. We tested the hypothesis that the altered metabolic phenotype of the failing heart involves changes in the protein expression of PPAR␣ and RXR␣. Methods and Results-Cardiac substrate uptake and oxidation were measured in 8 conscious, chronically instrumented dogs with decompensated pacing-induced heart failure and in 8 normal dogs by infusing 3 isotopically labeled substrates: 3 H-oleate, 14 C-glucose, and 13 C-lactate. Although myocardial O 2 consumption was not different between the 2 groups, the rate of oxidation of FFA was lower (2.8Ϯ0.6 versus 4.7Ϯ0.3 mol · min Ϫ1 · 100g