[Comparative study of the lymphoid organs of rats aboard a space flight under weightless and artificial gravity conditions].

A comparative histological investigation of the thymus, spleen and inguinal lymph nodes has been performed in the rats flown for 18.5 days on board the biosatellite "Cosmos-936" under the conditions of weightlessness and artificial gravitation (acceleration 1 g) imitating terrestrial magnetism. It has been stated that in the animals that were under the conditions of weightless ness during the flight and were sacrificed 4.5--13 h after they have landed the Earth, accidental involution of lymphoid organs is noted with morphological signs in them of an acute stress in the form of massive degeneration of the thymus lymphocytes and neutrophilic infiltration of the spleen. In rats that during the flight were subjected to the effect of artificial gravitation there was noted neither involution of the lymphoid organs nor morphological signs of acute stress in them. One of the main cause of acute stress in the rats subjected to weightlessness during the space flight is supposed to be transition to the terrestrial gravitation.