[Effects of simulated weightlessness on ultrastructures and oxygen supply and consumption of myocardium in rats].

Weightlessness causes atrophy of myocardium in rats, however, properties of ultra-structural changes and oxygen supply and consumption in myocardium are still unclear. Changes in ultrastructures of left ventricular myocardium in rats tail-suspended for 8W were observed. Qualitative analysis showed that the lysosomes, lipofuscins and degenerate mitochondria increased in myocytes of left ventricle in tail-suspended rats (SUS). The sarcoplasmic reticula were reduced in quantity and shrunken in appearance. The number of extended endothelial projections into the lumen of capillaries increased. Quantitative analysis showed that volume densities of mitochondria and sarcoplasmic reticulum in SUS were reduced by 14.5% and 22.2%, respectively. The number density of mitochondria also had a 12.5% decrease in SUS. The morphometric data-estimated oxygen demand of the myocardium in SUS showed a 16.7% decrease. These results suggested that the feature of the changes be chronic degeneration without the evidence of acute hypoxia in myocardium. The decrease of oxygen consumption of myocardium in SUS didn't cause a reflex reduction in the oxygen supply.