Immune and neuroendocrine responses to head-down rest and countermeasures

Head-down bed rest (HDBR) at -6 degrees is used as a model for studying physiological changes during microgravity in spaceflight. The aim of the present study was to investigate whether exposure to such an environment is associated with alterations in the synthesis of some acute-phase proteins and cytokines, and whether countermeasures would prevent these changes.

There were 12 male volunteers who were subjected to HDBR for 20 d; 6 formed the countermeasure (CMS) group and exercised on a short-arm centrifuge for 30 min/d, while the other 6 served as controls (CTL). Variables measured before and after HDBR included plasma noradrenaline, adrenaline, dopamine, leukocyte count, interleukin 6, total serum protein, C-reactive protein, and alpha-1 antichimotrypsin.

Adrenaline and noradrenaline concentrations increased significantly in both groups, while the concentration of C-reactive protein decreased. The concentration of C-reactive protein was significantly higher (CTL: 0.028 +/- 0.005 mg x dl(-1); CMS: 0.025 +/-0.003 mg x dl(-1)), and that of adrenaline was significantly lower in CTL compared to CMS (CTL: 46.8 +/- 7.5 pg x ml(-1); CMS: 71 +/- 22.5 pg x ml(-1)).

The results indicate that several neuroendocrine and immunological parameters are modulated by prolonged HDBR and these changes may be counteracted at least in part by artificial gravity with exercise.