[The effect of weightlessness on fracture healing of rats flown on the biosatellite Cosmos-2044]. / Vliianie nevesomosti na zazhivlenie perelomov kostei u krys, éksponirovannykh na biosputnike "Kosmos-2044".

Two days before launch of the biosatellite Cosmos-2044 five rats were exposed to surgical intervention: their fibulas were cut bilaterally. The purpose was to study the effect of microgravity on bone fracture healing. Histologically and histomorphometrically it was demonstrated that healing was inhibited; as a result, bone callus was poorly developed and bone fragment consolidation was inadequate. An increase in the relative volume of osteoid and a simultaneous decrease in the number and activity of osteoblasts point to mineral disorders of newly formed bone in microgravity. Study of untreated tibia showed that exposure to microgravity led to osteoporosis of proximal metaphyses. This osteoporosis was produced by inhibited neoformation and enhanced resorption of bone. Comparative analysis of injured fibula and untreated tibia of rats exposed to real microgravity for 14 days or tail suspended demonstrated similarity of changes. This indicates that tail suspension can be viewed as an adequate simulation of microgravity with respect to changes in hindlimb bones.

[Osteoporosis in monkeys after anti-orthostatic hypokinesia]. / Osteoporoz u obez'ian pri antiortostaticheskoi gipokinezii.

Using methods of quantitative histomorphometry, the effect of 15- and 30-day exposure to antiorthostatic hypokinesia (-10 degrees) on spongy bone of iliac crests and proximal metaphysis of tibia of Macaca mulatta was examined. It was found that the exposure caused osteoporosis of bone spongiosa. Osteoporotic changes increased progressively with time of exposure. Osteoporosis developed as a result of stimulated bone resorption, which was indicated by a greater resorption surface and a higher activity of osteoclasts, as well as inhibited bone neoformation, which was indicated by a lower osteoid volume. Comparative analysis of morphological changes in iliac and tibial bones demonstrated that they were distinct and similar in sign. Progressive development of osteoporosis gives evidence that 30-day antiorthostatic hypokinesia is insufficient for primates to get adapted to a new environment.

[Histomorphologic study of the bones of monkeys after 14-day anti-orthostatic hypokinesia]. / Gistomorfometricheskoe issledovanie kostei obez'ian posle 14-sutochnoi antiortostaticheskoi gipokinezii.

Using a semi-automatic image analyzer MOP Videoplan, a quantitative histomorphometric investigation of sponge bone of tibial metaphyses, iliac crests and lumbar vertebrae of monkeys kept for 14 days in the head-down position (at -10 degrees) was carried out. This exposure was found to cause spongy bone reduction in all the above bones. The lowered number and activity of osteoblasts as well as the reduced amount of osteoids during the exposure give evidence that the inhibition of bone neoformation makes a significant contribution to osteopenia. The involvement of osteoclast resorption in the spongiosa reduction during head-down tilt needs further study because in our experiments the osteoclast number or acid phosphatase activity did not grow significantly.

[Morphologic and biochemical study of the functional state of the adrenal cortex in the rat during prolonged hypokinesia]. / Morfologicheskoe i biokhimicheskoe issledovanie funktsional'nogo sostoianiia kory nadpochechnikov krys pri dlitel'noi gipokinezii.

Female rats exposed to 3-month hypokinesia were used to study adrenal morphology and plasma corticosterone. Prolonged hypokinesia (60-90 days) led to a dissociation between adrenal hypertrophy and lower corticosterone content in plasma. During hypokinesia rats were also exposed to an additional stress-effect, i.e. 5-hour immobilization. This approach showed that in the course of 90-day hypokinesia the adrenal cortex retained its ability to react to an acute stress by an enhanced corticosteroid secretion. Moreover, in response to stress-effects of identical strength and duration the experimental adrenals produced more corticosterone than the controls with no structural rearrangement or de-lipoidization.

[Adrenal function of rats in hypokinesia]. / Funktsional'noe sostoianie nadpochechnikov krys pri gipokinezii.

Histological and biochemical examinations of the adrenals and plasma of rats for 3 months exposed to hypokinesia have shown that low motor activity led to a decrease in blood corticosterone level in spite of adrenal cortex hypertrophy. The decreased corticosterone blood level was not indicative of adrenal exhaustion, as the adrenals produced a greater amount of corticosterone in response to additional stress stimulus (5-hour immobilisation of animals in an extended state), as compared to the control. The increased production of corticosterone in response to stress stimulus caused no structural transformations or delipoidization of the cortical substance. This indicated that the reserve potentials of the adrenals increased with the animal adaptation to hypokinesia. The major morphological indication of higher adrenal functional activity in hypokinetic animals was an enhanced destruction of lymphocytes in the thymus cortex, the target organ for corticosteroids produced by the adrenals in response to an additional stress stimulus.

[Morphological manifestations of acute stress reactions in the adrenal cortex of hypokinetic rats]. / Osobennosti morfologicheskikh proiavlenii ostroi stressovoi reaktsii v kore nadpochechnikov u krys na fone gipokinezii.

Adrenal changes in response to an acute stress-effect (5 h-immobilization stress) were investigated in female rats exposed to hypokinesia for 3 months. The rate of delipoidization in the adrenal cortex increased in the rats exposed to an acute stress after short-term (1-2 weeks) hypokinesia. The process of delipoidization did not advance in the rats exposed to an acute stress in the course of prolonged (2-3 months) hypokinesia. This does not yet prove the lack of the stress reaction but gives evidence that during prolonged hypokinesia the adrenals develop the capacity to react to an additional effect without the entire complex of morphological signs typical of an acute stress reaction. The immobilization test used to assess the state of the adrenal cortex has shown that it does not deteriorate even during 3-month hypokinesia (in this study).

[Reactions of the lymphoid organs of the rat to acute stress in hypokinesia]. / Osobennosti reaktsii limfoidnykh organov krys na ostroe stressornoe vozdeistvie pri gipokinezii.

Female rats long exposed to hypokinesia were then subjected to an acute stress. In this situation the thymus and spleen were examined. The destructive process in the thymus increased in spite of its hypoplasia. This can be attributed to a greater production of corticosteroids by the adrenals caused by the chronic stress. At the same time the white pulp of the spleen decreased insignificantly because it contained no lymphocytes capable to migrate by the time of the acute stress-effect. It is concluded that enhanced destruction of lymphocytes in the thymus in response to an acute stress can be regarded as a diagnostic test of the adrenal state during a chronic stress-effect, including hypokinesia.