Are energy metabolism alterations involved in cardiovascular deconditioning after weightlessness? An hypothesis.

The physiopathogenesis of the cardiovascular deconditioning syndrome observed after actual and simulated microgravity is still under debate, despite numerous studies conducted on the role of blood volume, hormones involved in its regulation, sympathetic nervous system, baroreflexes and venous compliance. Orthostatic intolerance, a reduced exercise capacity and an increased heart rate at rest characterize this syndrome. Recent data suggest, first, the presence of a complex loop between the sympathetic nervous system, carbohydrate metabolism (insulin) and leptin hormone and, second, that this loop, an overall reflection of energy metabolism, participates in cardiovascular regulation. After a resume of studies conducted on fuel homeostasis during actual and simulated microgravity, the possible implications of energy metabolism in the development of the cardiovascular deconditioning syndrome will be discussed.