Effect of parabolic flight on plasma arginine vasopressin as a sensitive marker for psychophysiological stress in humans

A number of parabolic flight experiments have shown that processes within the central nervous system (CNS) are affected by weightlessness in humans. However, it is likely that the changes in the CNS observed during parabolic flights are not solely due to the repeated changes in gravity experienced during the flight. Instead, these changes may be related to secondary psychophysiological reactions related to the emotional and physical stress during these flights. Arginine vasopressin (AVP) acts synergistically with corticotropin‐releasing hormone to stimulate corticotropin release from the anterior pituitary, and it is critical in the regulation of hypothalamic‐pituitary‐adrenal axis activity, a major component of the stress response. The purpose of this study was to elucidate whether stress‐related humoral factors, namely, AVP, were altered in human blood exposed to gravity‐changing stress. Parabolic flight‐naive subjects were exposed to gravity‐changing stress eight times during repeated parabolic maneuvers performed by an airplane. Concentrations of AVP, cortisol, and catecholamines were increased just after the parabolic flight without hematocrit alterations. The results of the present study suggest that the plasma concentration of AVP behaves as a stress hormone and might be a sensitive humoral marker for psychophysiological stress in humans.