Cardiovascular deconditioning effects of long-term simulated weightlessness in rats

The aim of our serial work was to investigate the cardiovascular deconditioning effect of long-term simulated weightlessness and to elucidate its mechanisms. Our research goal was established in view of the following three reasons. Firstly, even after several decades of extensive research, there still exist significant gaps in our knowledge concerning microgravity induced cardiovascular effect. Secondly, to guarantee the health and safety of astronauts in the future prolonged missions, it is important to understand the cardiovascular adaptation to long-term weightlessness. Thirdly, the reported ultrastructural degenerative changes in myocardium of rats flown on the Cosmos 1887 biosatellite has raised concerns about the question whether long-term spaceflight may lead to myocardial degeneration. To achieve this, we considered an appropriate animal model to simulate cardiovascular and other effects of long-term microgravity was of first importance. By making some modifications to the Morey-Holton's model, a method of long-term tail-suspension with less stressful influence and no injurious effects on the tail skin was developed. Up to now, the longest period of suspension in our laboratory has been of 120-day long. In this paper, we will focus primarily on the findings from our recent works on the cardiovascular deconditioning effect of 90-/120-day tail-suspension and changes in baroreflex responsiveness and in contractility and ultrastructure of the heart in rats.