Without training in orbit capillaries can be lost

Specialists of the pathologic laboratory of the Research Institute of General Pathology and Pathophysiology (Russian Academy of Medical Sciences), who have discovered this fact with rats, point out that this is a temporary disorder. On the Earth, blood vessels grow up again but their regeneration takes much more time than their ruining.

Subject of inquiry was laboratory rats that stayed on board the SLS-2 satellite (Spacelab Life Sciences, USA). The researchers used for analysis the muscles lifting up the rat’s pollex. The muscular tissue samples were taken in orbit on the 14th day of the flight, and on the 1st and the 14th day after return to the Earth. Ultrastructural investigation has shown that all rats had disrupted cellular wall integrity, vascular permeability and microcirculation in the muscles. Considerable part of capillaries was irreversibly injured. The cells forming the vascular wall perished, arterial and venous capillary lumens are occupied by cytoplasm from destroyed cells and by collagen fibrils. Small lymphatic vessels look no better.

In the state of weightlessness, skeletal muscles are relaxed (at any case, muscles of rats, which, in contrast to human beings, are not trained to make special exercises). Without load, muscle fibers gradually mortify, and after than the capillaries feeding them get destroyed and mortify. Half-ruined arterioles are unable to supply muscles with oxygen, but venules and lymphatic vessels are permorming drainage functions. The remaining capillaries do not provide for normal microcirculation, therefore, the remaining muscles suffer from edema and hypoxia, and this in its turn provokes further destruction of the smallest blood vessels.

Capillaries also suffer from physical factors, acceleration and weightlessness, which probably impact the cellular membrane permeability and results in necrosis of the cells lining the vessel walls. The cells get lost very quickly and are not replaced by new ones as it happens in case of microvessel necrosis under some diseases, for example, diabetes or after a trauma.

In the researchers’ opinion, one of the reasons for quick capillary injury in outer space is that the animals are not trained. Training helps the cells to promptly adapt themselves to overload and weightlessness conditions and enables their “adaptation reserve” required to overcome overload, but untrained cells have no time to do that.

After return to the Earth, new capillaries are gradually formed in the rat’s muscle. However, their regeneration requires much more time than destruction. Even after two weeks in gravitation conditions, the researchers still observed destroyed microvessels in the muscles.