Effects of bilateral vestibular lesions on the arterial pressure response to neck flexion

Abstract

Our previous study reported that 45° head-down postural rotation (HDR) induced a transient decrease in arterial blood pressure (ABP) in anesthetized rabbits. We hypothesized that vestibular organs induce a decrease in the ABP through the inhibition of the sympathetic neural outflow during HDR. To test this hypothesis, we examined the responses of the ABP and renal sympathetic nerve activity (RSNA) to neck flection (NF) in urethane-anesthetized rabbits. The animals were placed on a table in the prone horizontal position. The head was rotated downward to a 45° NF position over 5 s and maintained in that position. NF induced a suppression of the RSNA, followed by a transient decrease (11 ± 3 mmHg ; mean ± SE) in the mean ABP at 7.4 ± 0.4 s after the onset of NF. NF in the lateral position did not induce a significant change. The administration of hexamethonium bromide suppressed the NF-elicited decrease in the ABP, suggesting that this decrease was induced by the suppression of the autonomic neural outflow. In vestibular-lesioned animals, the ABP did not show a significant decrease during NF. These results suggest that head-down rotation around the left-right axis through an HDR and NF stimulates the vestibular organs, which likely elicits a decrease in the ABP via the inhibition of sympathetic activities.