Functional interaction between baroreflex and vestibulo‐sympathetic reflex upon head‐up tilt

Abstract

Head‐up tilt (HUT) elicits gravitational fluid shift and a decrease in arterial pressure (AP), which is thought to be buffered by baroreflex and vestibulo‐sympathetic reflex. However, functional interaction between these reflexes has not been clear. To examine this, renal sympathetic nerve activity (SNA) and AP were measured in anesthetized, vagotomized, and aortic denervated rats with or without vestibular lesion (VL). Isolated carotid sinus pressure (CSP) was increased stepwise from 60 to 180 mmHg with increments of 20 mmHg (30–60 s for each CSP level) while the rat was placed prone flat position and at 60° HUT. HUT shifted the CSP‐SNA relationship (the baroreflex central arc) to a higher SNA, shifted the SNA‐AP relationship (the 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, while the peripheral arc shifted to a lower AP; the operating point moved to a lower AP (−26 mmHg). These results indicate that the vestibular system elicits sympathoexcitation upon HUT and shifts the baroreflex central arc to a higher SNA and then maintain baroreflex operating AP.