Role of the vestibular system in sudden shutdown of renal sympathetic nerve activity during microgravity in rats

The purpose of this study was to examine the effect of microgravity (mu G) on renal sympathetic nerve activity (RNA) in rats. Additionally, we estimat ed the participation of the vestibular system in the response of RNA to mu G. Eight normal Sprague-Dawley (SD) rats and five chemically and bilaterall y labyrinthectomied SD rats were used to measure RNA during free-drop exami nation (4.5-s duration of mu G); arterial pressure IAP) and aortic flow vel ocity (AFV) were additionally monitored. Although AFV showed no particular change, AP tended to decrease during mu G in the later phase. Prior to this AP fall-off, RNA was immediately and markedly attenuated by mu G. This att enuation was transient and RNA returned to 1G level within the mu mu G cond ition. Interestingly, this phenomenon remained even in labyrinthectomied ra ts. In conclusion, cephalad shift of the body fluid by loading of mu G may cause cardiopulmonary low-pressure receptor activation and consequent RNA a ttenuation, but the participation of the vestibulosympathetic reflex in thi s phenomenon is not obvious. (C) 2000 Elsevier Science Ireland Ltd. All rig hts reserved.