Calibrated histochemistry applied to oxygen supply and demand in hypertrophied rat myocardium

Abstract

Oxygen supply and demand of individual cardiomyocytes during the development of myocardial hypertrophy is studied using calibrated histochemical methods. An oxygen diffusion model is used to calculate the critical extracellular oxygen tension (PO(2,crit)) required by cardiomyocytes to prevent hypoxia during hypertrophic growth, and determinants of PO(2,crit) are estimated using calibrated histochemical methods for succinate dehydrogenase activity, cardiomyocyte cross-sectional area, and myoglobin concentration. The model calculation demonstrates that it is essential to calibrate the histochemical methods, so that absolute values for the relevant parameters are obtained. The succinate dehydrogenase activity, which is proportional to the maximum rate of oxygen consumption, and the myoglobin concentration hardly change while the cardiomyocytes grow. The cross-sectional area of the cardiomyocytes, which increases up to threefold in the right ventricular wall due to pulmonary hypertension in monocrotaline-treated rats, is the most important determinant of PO(2,crit) in this model of myocardial hypertrophy. The relationship between oxygen supply and demand at the level of the cardiomyocyte can be investigated using paired determinations of spatially integrated succinate dehydrogenase activity and capillary density. Hypoxia-inducible factor 1alpha can be demonstrated by immunohistochemistry in cardiomyocytes with high PO(2,crit) and increased spatially integrated succinate dehydrogenase activity, indicating that limited oxygen supply affects gene expression in these cells. We conclude that a mismatch of oxygen supply and demand may develop during hypertrophic growth, which can play a role in the transition from myocardial hypertrophy to heart failure.

The effects of caloric restriction and age on thyroid hormone signalling in the heart of rats

“…Such an effect was already observed after 7 days of 50% caloric restricted feeding of mice (Gruber et al, 2012). Cardiomyocyte hypoxia has also been observed in cardiac hypertrophy as cardiomyocyte diameter increased and oxygen diffusion deteriorated (Des Tombe et al, 2002). This would not be the case in our experiment, however, since caloric restriction has been shown to reduce cardiac hypertrophy (Ahmet et al, 2011).…”

American Thyroid Association Guide to Investigating Thyroid Hormone Economy and Action in Rodent and Cell Models

“…The weight of the whole heart or individual ventricles should preferably be determined as a ratio to tibia length, since body weight may vary considerably as a function of the thyroid status. H&E staining of paraffin sections is typically used for measurement of cardiomyocyte cross-sectional area (238,567). It should be noted that the conditions of fixing cardiac tissue can affect cardiomyocyte morphology and additional methods have been developed to determine accurately myocyte cross-sectional area as well as length (539).…”

PET imaging of cardiac hypoxia: Opportunities and challenges

“…In this context, ischemia and hypoxia contribute to the pathophysiology of heart failure, but since its clinical presentation is typically less dramatic and more diffuse than acute myocardial infarction, and can occur in the absence of coronary artery disease, our inability to detect it means that we are missing an important opportunity to intervene. This decreased vascularity in hypertrophic myocardium is exacerbated by increases in myocyte size and tissue fibrosis, which increase diffusion distances and decrease oxygen availability to myocytes (and perhaps more importantly, their mitochondria) [27,28]. While up-regulation of hypoxia inducible factor HIF-1α is increasingly being recognized as an important instigator of cardiac hypertrophy [29][30][31] and mediator of decline into heart failure [32][33][34], we have found no reports that successfully demonstrate non-invasive measurement of hypoxia itself in hypertrophic or failing myocardium.…”