Hypoxia Hits Below the Diaphragm: Effect of Acute Hypoxia on the Micturition Reflex

Abstract

While changes in respiratory drive and associated respiratory motor function during acute hypoxia are well documented, the effect of acute hypoxia on non‐respiratory somatic or autonomic motor systems is less well studied. The goal of the present study is to characterize the effect of acute hypoxia on lower urinary tract (LUT) function with a specific focus on reflex micturition. In urethane‐anesthetized, spontaneously breathing adult female Sprague Dawley rats, bladder intravesical pressure and external urethral sphincter (EUS) EMG activity were recorded during continuous infusion of saline into the bladder to elicit reflex micturition events. The rate of saline infusion was adjusted to achieve a baseline bladder inter‐contraction interval (ICI) of approximately 4 minutes. After 30–40 minutes of baseline recording, rats were exposed to a single episode of sustained hypoxia (10–12% O2; balance N2) with a duration of 1.5, 5 or 15 minutes followed by return to room air. The episodes of hypoxia were initiated approximately midway during bladder filling and consistently produced a premature reflex micturition event. During the 5‐ and 15‐minute episodes, the reduction in ICI continued for the duration of the hypoxia and was associated with a decrease in bladder pressure threshold (reduced intravesical pressure at the onset of active bladder contraction), particularly during 15‐minute exposures. No consistent change in EUS activity during hypoxia was observed. Following return to room air, the subsequent reflex micturition event was delayed, particularly after 5‐ and 15‐minute episodes of hypoxia, and the increase in ICI was associated with increases in both bladder pressure threshold and EUS activity during bladder filling (increased EUS guarding reflex). These data suggest that acute hypoxia alters LUT function and that both autonomic and somatic components of the micturition reflex are sensitive to hypoxia.Support or Funding InformationSupport for this project was provided by The Thomas Hartman Center for Parkinson's Research at Stony Brook University and The SUNY Brain Network of Excellence.