Changes in some biochemical and physiological indexes after hypergravitation

The purpose of this study was to assess the G-tolerance and G-induced changes in plasma renin activity (PRA), serum cortisol, testosterone, thyroid hormones and blood concentrations of serotonin and histamine. Experiments were performed on 26 student pilots aged 22.7 +/- 0.7 years using simulated aerial combat manoeuvres (SACM) in a centrifuge with radius 7.5 m. G-tolerance was assessed by loss of vision criteria, G-induced loss of consciousness and significant disturbances in heart rhythm. PRA, cortisol, testosterone and thyroid hormones were measured by radioimmunoassay, serotonin and histamine by spectrofluorimetric methods 24 hours before and 5 min after SACM. The statistical significance of hypergravitation and G-tolerance were determined by ANOVA. We found a significant increase in PRA (p = 0.001) and thyroxine concentration (p = 0.005) after hypergravitation loads. It is known that these changes are indicative for cardiovascular adaptation and enhancement of energy mobilization. Histamine levels differed significantly by G-tolerance (p = 0.031), while serotonin concentrations changed by hypergravitation (p = 0.004). Significant dependence on hypergravitation x G-tolerance was found for serotonin values (p = 0.024). Studying G-induced hormonal changes can reveal individual peculiarities in G-tolerance, a limiting factor for the exploitation of high performance aircraft.