The reduction of capillary density in microgravity- induced muscle atrophy has been observed by several studies. Molecular mechanisms leading to this changes remain unknown. Therefore, my studies were designed at testing endothelial reactions on microgravity that are probably connected to the regulation of blood vessel growth. This book presents the results of research on the expression of NEDD4 in endothelial cells, the impact of microgravity and different flow patterns on it, as well as NEDD4 mediated degradation of Cx43 under these conditions. In addition, previous studies revealed that ADAMTS1, which plays a pivotal role in the regulation of angiogenesis, is strongly induced by shear stress. Here, it was also investigated if there is any influence of microgravity on ADAMTS1 expression. These results provide a better understanding of mechanisms which can contribute not only to the development of different pathological situation observed in astronauts, but also for patients during long bed rest.