Myocardial Feulgen-DNA levels and capillary vascularization in hypoxia-exposed rats

Male abino rats were exposed to simulated altitude of 18,000 ft (380 Torr) for 1 day to 8 wk. Histological sections of heart ventricles were stained by the Feulgen technique and amounts of Feulgen-DNA were determined cytophotometrically. Heart weights, relative to body weights, increased over controls at all exposure periods, as did myocardial capillary vascularization. Ninety percent of cardiac muscle nuclei were found to contain tetraploid amounts of DNA. All nuclei exhibited a high degree of chromatin dispersion in exposed and unexposed rats, which reflects a highly reactive metabolic state of cardiac cells in both groups. There was no evidence of increased ploidy or increased DNA synthesis associated with hypertrophy after acute or chronic hypoxia exposure. The data suggest that an initial event which could facilitate augmented protein synthesis during hypoxia acclimation appears to be an increased availability of oxygen and/or nutrients brought about by an expansion of the capillary bed and vascular proliferation.