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The pilot study indicates that the excretion of o-hydroxy hippuric acid in urine is a useful addendum to the molecular determinants of stress and, under controlled conditions, may aid in identifying candidates who can or cannot succeed as test parachutists. In concurrent experiments all parachutists studied showed a significant increase in plasma phosphatidyl glycerol, a sensitive and proven indicator for stress. Further studies have shown that the distribution of cyclic AMP in living tissues is ubiquitous and that increased tissue levels are associated with beta adrenergic reactions. It was postulated that changes in tissue cyclic AMP levels might be correlated with physiological changes resulting from the application of whole body stresses, and that tissue cycle AMP could be used as an indicator of physiological stress.

The observed changes of phase and signal amplitude of VLF radio waves, propagated over distances varying between 1000 and 10000 km, which accompany solar flares have been studied for the period 1961-1964. In general the phase of the received signal advances and the signal amplitude increases during the onset of a solar flare. However observations of the GBR transmissions at Rome (1500 km path) show that for this particular path the phase of the received signal retards in contrast to all other paths studied. Assuming that the conductivity of the lower ionosphere varies exponentially with height under both quiet and disturbed conditions, it is possible to evaluate the waveguide mode characteristics of VLF propagation over large distances. Using this theoretical approach it has been shown that the observations can only be interpreted if both the D region electron density profile is lowered and the gradient of ionisation density increased. The magnitude of the flare produced changes in ionisation density profiles of the lower ionosphere have been evaluated analytically from solar X-ray data. These profile changes are consistent with the lowering of the D region and increase in ionisation gradient that is required to explain the VLF radio wave observations. (Author)