[Adaptation to weightlessness and stress].

The literature on the problem of stress-inducing effect of weightlessness is reviewed. On the basis of scrupulous analysis of the data accumulated in the rat flight experiments aboard the Cosmos biosatellites and the US Space Life Sciences Laboratory (SLS-2) it is concluded that although the ever-acting factor of space mission, microgravity does not cause any intensive chronic stress to animals. Nonetheless, it contributes to the development of deconditioning of a number of vitally important systems and the body as a whole. On return to Earth, the usual terrestrial loads due to the gravity effects are perceived by the deconditioned animals as extraordinary and they respond by severe gravitational stress.