Abstract
We reported previously that a transient drop in arterial blood pressure (ABP) was induced by head down rotation (HDR) in urethane-anesthetized rabbits. Our results suggested that vestibular inputs due to HDR played a role in the drop of ABP possibly through sympathetic nerve outflows. However, the anesthetic agent may have influences on control of ABP and vestibular inputs. Accordingly, it is important to examine ABP changes during HDR using conscious animals. A week before the experiment, a catheter was inserted from the left carotid artery and was positioned in the aorta at the level of the aortic arch to monitor blood pressure. Chemical labyrinthectomy was applied by injecting 20 mg/kg sodium arsanilate into the bilateral intratympani two days before the experiment. In control rabbits, the same amount of saline was injected instead of the sodium arsanilate. On the experiment day, the animal was mounted comfortably on a tilting table in a dark room. The animal was tilted to 45-degree head-down within 5 s and kept at the position for 1 minute. HDR increased the ABP (from 108 ± 4 mmHg to 118 ± 8 mmHg) and kept the pressure at the increased level until the end of HDR in the control alert rabbits. HDR in vestibular-lesioned (VL) rabbits increased the ABP from 103 ± 6 mmHg to 120 ± 7 mmHg. The increase in VL rabbits (117 ± 3%) was significantly larger than that (110 ± 3%) in controls. These results suggest that vestibular organs are involved in the control of ABP during HDR. [J Physiol Sci. 2008;58 Suppl:S108]
