Daily head-up tilt, standing or centrifugation can prevent vasoreactivity changes in arteries of simulated weightless rats

Artificial gravity will be considered for long-duration spaceflight missions. Recent studies have shown that continuous exposure to gravity does not appear necessary to prevent the adverse effects of weightlessness, instead intermittent exposure may suffice. Vernikos et al reported that 1 G intermittent exposures with and without walking exercise was effective in preventing physiologic deconditioning with 4-d, -6 degrees bedrest, and standing at 1 G was most effective in preventing orthostatic intolerance. Our previous work has demonstrated differential adaptational changes in structure, function, and innervation state of arterial vasculature in different body regions of rat during simulated weightlessness and further suggested that these changes might be one of the most important mechanisms accounting for postflight orthostatic intolerance. We therefore designed the present study involving a comprehensive evaluation of the effect of intermittent G exposure in preventing the differential functional changes of the arteries at the end of 3-wk head-down tail suspension in rats to answer the following questions: (1) do intermittent G exposure have counteracting effect in preventing differential functional changes in arterial vasculature with tail-suspension? (2) among the treatments used in the present study, i.e., head-up tilt (HUT), standing (STD), and centrifugation (CEN), what kind of exposure is more effective? (3) how much time in daily 1 G exposure is needed to maintain the normal (1 G) vascular responsiveness?