[Morphological and biochemical analysis of the organs and tissues of rats following a 30-day exposure to increased gravitational forces of 1.1 and 2.0 G].

During 30 days rats were centrifuged at 1.1 and 2.0 G. On centrifugation day 30 the rats showed body mass losses, decrease of plasma ACTH, activation of the renin-angiotensin-aldosterone system (RAAS) and ultrastructural changes in the mossy fiber terminals in the nodulus cortex which were indicative of the state of excitation (at 1.1 G) or excess excitation (at 2.0 G) in the system of the utriculus receptor cell and vestibular ganglion neuron (RCN). On the 2nd day after centrifugation the ultrastructural changes in the terminals pointed to a lower activity of the RCN system which was below the physiological norm. As compared to centrifugation day 30, the RAAS became more active on the 2nd day of recovery. On the 7th day of recovery (after centrifugation at 1.1 G) the RCN ultrastructure, RAAS and ACTH concentrations returned to the normal. The general trends of the RAAS and RCN changes seen on the 2nd day of recovery and identified by other authors at an acute stage of adaptation to microgravity suggest that the data obtained on the 2nd day of recovery may be used to analyze certain effects which develop during an acute stage of adaptation to microgravity in mammalian organs and systems responsible for the perception of modified gravity and their adaptation to a new level of gravity.