The effect of hypergravity environment on vestibulo‐cardiovascular reflex in conscious rats

Abstract

We have demonstrated that the vestibular system has a significant role in the arterial pressure (AP) response during gravitational change in conscious rats. The vestibular system is known to be highly plastic; i.e., the plasticity of the vestibulo‐ocular and vestibulo‐spinal reflex. Resent study from our laboratory demonstrated the plasticity of the vestibulo‐cardiovascular reflex. Microgravity‐induced pressor response was significantly attenuated if 8 weeks old rats were reared under 3 G environment for 2 weeks. Thus, the vestibulo‐cardiovascular control system which was constructed under 1 G environment was altered by 3 G environment for 2 weeks. However, it is still unclear whether the AP response via the vestibular system might be altered if the vestibulo‐cardiovascular control system is constructed under different gravitational environment. Accordingly, the aim of the present study was to examine whether the vestibular‐mediated AP response might be altered if rats were born and developed under hypergravity environment. To examine this, the AP response to linear acceleration was examined in conscious rats which were born and developed under usual 1 G or 2 G condition. ± 1 G linear acceleration of four directions, in which tail‐to‐nose, nose‐to‐tail, left‐to‐right and right‐to‐left acceleration, was employed. The AP of the 1‐G rat was increased by 24 ± 1 mmHg in the tail‐to‐nose, 19 ± 1 mmHg in the nose‐to‐tail, 20 ± 1 mmHg in the left‐to‐right and 21 ± 1 mmHg in the right‐to‐left acceleration. This pressor response was significantly attenuated in the 2‐G rat in all directions. However, there was no significant difference in the AP response during air jet stimulation between 1‐G and 2‐G rats. These results indicate that the vestibulo‐cardiovascular control system was specifically altered if rats were born and developed under 2 G environment.