Influence of hypergravity environment on interaction between baroreflex and vestibulo‐sympathetic reflex during head‐up tilt

Abstract

Because arterial pressure (AP) decreased during rear‐up in rats with baroreceptor denervation or vestibular lesion (VL), baroreflex and vestibulo‐sympathetic reflex cooperate to maintain AP during rear‐up. Functional interaction between these two reflexes was examined. Isolated carotid sinus pressure (CSP) was increased stepwise from 60 to 180 mmHg, while rats were placed prone flat position or at 60° head‐up tilt (HUT). HUT shifted the CSP‐sympathetic nerve activity (SNA) relationship (baroreflex central arc) to a higher SNA, shifted the SNA‐AP relationship (baroreflex peripheral arc) to a lower AP, and consequently moved the operating point to high SNA while maintaining AP. In VL rats, the HUT‐induced central arc shift was completely abolished; the operating point moved to a lower AP. Thus, the vestibular system elicits sympathoexcitation upon HUT and shifts the baroreflex central arc to a higher SNA. However, the vestibular system is known to be highly plastic, i.e., if rats were maintained under different gravitational environment, vestibular sensitivity might be reduced. Thus, influence of hypergravity environment on functional interaction between baroreflex and vestibulo‐sympathetic reflex was further examined.