1,721,223 research outputs found
Morphometry of right ventricular hypertrophy induced by strenuous exercise in rat.
No full textEffects on the myocardium, particularly those structural properties of the capillary network relevant to tissue oxygenation, were studied morphometrically in rats subjected to a severe running program. Physical conditioning produced a 31% increase in right ventricular weight and only a 12% increase in the weight of the left ventricle. Quantitative analysis of right ventricular myocardium demonstrated relative decreases in capillary luminal volume density (-27%) and capillary luminal surface density (-20%) and an increase in the average maximum distance from the capillary wall to the mitochondria of myocytes (14%). In contrast, the contractile mass expanded in proportion to the growth of the ventricle through augmentation of the cross-sectional area (17%) and length (19%) of the average myocyte. Evaluation of the subcellular constituents of myocytes showed no change in the mitochondria-to-myofibril volume ratio. In conclusion, the capillary bed controlling oxygen availability, diffusion, and transport suggests that excessive physical activity may be detrimental to the myocardium
Morphometry of right and left ventricular myocardium after strenuous exercise in preconditioned rats.
No full textYoung male rats were exposed to a biphasic training program in which a 7-week preconditioning period of moderate treadmill exercise was followed by 8 weeks of strenuous endurance running. In comparison with sedentary control animals, the trained rats at 20 weeks of age had developed myocardial hypertrophy of the right ventricle (20%) and interventricular septum (23%), but there was no difference in the weight of the left ventricular free wall. Myocyte hypertrophy (26%) in the right ventricle was achieved through an increase in mean cell length (24%) and the addition of new sarcomere units in series. Exercise induced no acceleration of capillary growth in either ventricle, leading to significant decreases in the capillary luminal volume density (-21%) and surface density (-16%) in the right ventricle. Such alterations in the structural properties of the microvasculature implicated in oxygen availability and diffusion suggest that vigorous exercise, even after a preconditioning period, may still be detrimental to the myocardium. The techniques of myocardial morphometry were examined with respect to potential errors associated with oblique tissue sections and the use of light versus electron microscopy for cell counting. It was shown that the practical effects of obliquity are negligible and that electron microscopic resolution is essential
Myocardial infarction in rats. Infarct size, myocyte hypertrophy, and capillary growth.
No full textTo determine the compensatory reserve capacity of the ventricular myocardium following infarction, the left coronary artery in rats was ligated, and the animals were killed 40 days later. Infarcts affecting an average 23% of the left ventricle were characterized by a 27% hypertrophic growth of the remaining myocardium that produced a complete replacement of the necrotic tissue. In contrast, infarcts with an average 50% loss of mass resulted in 83% expansion of the spared myocardium that was inadequate for a complete restoration of ventricular tissue. Myocyte hypertrophy was 26% and 78% in small and large infarcts, respectively. Cellular hypertrophy in both cases involved significant increases in myocyte transverse area and myocyte length. After large infarcts, there was an 18% reduction in capillary surface and a 16% increase in the diffusion distance. Corresponding values for small infarcts were -10% and 9%. These alterations combined with the deficient reconstitution of myocardial mass following large infarcts resulted in 25%, 29%, and 30% deficits in the absolute amounts of capillary lumen, surface, and length per ventricle respectively. Even with small infarcts, a deficit was seen in capillary luminal surface (-16%), and length (-19%). In conclusion, we have demonstrated that cardiac hypertrophy following myocardial infarction is consistent with cellular shape changes characteristic of a combination of concentric and eccentric hypertrophic growth. However, cardiac muscle cells appear to be unable to compensate for the loss of mass induced by a 50% infarct. The inadequate adaptation of the capillary vasculature in the infarcted hearts suggests that the injured ventricle is more vulnerable to additional ischemic episodes
Morphometry of exercise-induced right ventricular hypertrophy in the rat.
No full textIn our morphometric study of the effects of exercise on the heart, male Wistar-Kyoto rats at 5 weeks of age were subjected daily to a moderate treadmill running program that lasted for 7 weeks. The heart responded to physical conditioning by different magnitudes of tissue growth of the right (22%) and left (7%) ventricular myocardium, the latter change not statistically significant. The increase in right volume was associated with a 25% enlargement of ventricular area, a 26% average lengthening of the myocytes, and no change in sarcomere length and in ventricular midwall thickness. Exercise produced significant alterations in the quantitative parameters of the microvasculature of the right ventricle, but no appreciable changes in the left ventricle. Right ventricular hypertrophy was characterized by an absolute 44% growth of the endothelial luminal surface brought about through a 16% increase in capillary numerical density, and a 41% augmentation of the total length of the capillary network. Maximum diffusion distance from the capillary wall to the mitochondria of myocytes decreased 10% as a result of capillary proliferation and the lack of lateral expansion of myocyte cross-sectional area. Evaluation of the subcellular constituents of myocytes showed no change in the mitochondria:myofibrils volume ratio indicating a growth of these components proportional to each other and to the growth of the myocyte population as a whole. It was concluded that, as a result of running exercise, right ventricular growth is nalogous to eccentric hypertrophy in which the structural adaptations of the capillary bed can be expected to improve the diffusion and transport of oxygen within the tissue
Myocardial response to infarction in the rat. Morphometric measurement of infarct size and myocyte cellular hypertrophy.
No full textFor determination of the effects of myocardial infarction on the recovery potential of muscle mass in the surviving tissue, ligation of the left coronary artery was performed in 3-month-old rats, and the infarcted ventricles were analyzed morphometrically a month after surgery. Comparisons were made with 4-month-old control rats that underwent sham operations and with 3-month-old controls rats that were not operated upon for evaluation of the magnitude of infarct size and discrimination of the relative contribution of tissue growth that occurred in the surviving myocardium solely as a result of the change in age, from 3 to 4 months (postoperative tissue growth, or POTG), from the additional growth induced by infarction (hypertrophic growth, or HG). Coronary occlusion induced a 276-cu mm loss of ventricular tissue volume that corresponded to 43% of the total left ventricular mass, 648 cu mm. Over a 30-day period the remaining 372 cu mm of viable tissue expanded by 90% with an overall volume gain of 334 cu mm. This tissue augmentation consisted of 20% POTG, 67 cu mm, and 80% HG, 267 cu mm. Total myocyte volume increased 89%, from 302 cu mm to 571 cu mm, and average myocyte cell volume per nucleus increased 92%, from 16,500 cu μ to 31.600 cu μ. The expansion of the myocyte mass was the result of a 21% POTG and a 79% HG. Corresponding values for the myocyte population were 19% and 81%
Coronary artery spasm in the rat induced by hypothalamic stimulation.
No full textAnesthetized rats were sterotaxically implanted with electrodes and electrically stimulated in the lateral hypothalamus. During elevation of the S-T segment on simultaneous precordial electrocardiograms, the heart was perfused with glutaraldehyde-paraformaldehyde fixative and the major coronary arteries prepared for morphometry of luminal dimensions. A similar procedure was performed in a second group receiving intravenous arginine vasopressin (AVP) in place of hypothalamic stimulation. Elevation of the S-T segment was present in these animals as well. Control animals were implanted, not stimulated and otherwise treated in the same way. Morphometry showed that reductions of mean luminal diameter and cross-sectional area of statistical significance occurred in the two experimental groups compared to controls, suggesting that coronary spasm was the cause of the elevated S-T segments. Pooled plasma from separate groups of implanted control and hypothalamically-stimulated animals revealed substantial elevation of AVP levels in the latter raising the possibility that the neuroendocrine was involved in eliciting coronary artery spasm
Origin of cardiomyocytes in the adult heart
No full textThis review article discusses the mechanisms of cardiomyogenesis in the adult heart. They include the re-entry of cardiomyocytes into the cell cycle; dedifferentiation of pre-existing cardiomyocytes, which assume an immature replicating cell phenotype; transdifferentiation of hematopoietic stem cells into cardiomyocytes; and cardiomyocytes derived from activation and lineage specification of resident cardiac stem cells. The recognition of the origin of cardiomyocytes is of critical importance for the development of strategies capable of enhancing the growth response of the myocardium; in fact, cell therapy for the decompensated heart has to be based on the acquisition of this fundamental biological knowledge
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