Effect of Repetitive Stimulation on the Contractile Response of Rabbit Urinary Bladder Subjected to in vitro Hypoxia or in vitro Ischemia Followed by Reoxygenation

Abstract

Purpose: We studied the effects of hypoxia followed by reoxygenation and an in vitro model of ischemia (hypoxia + substrate [glucose] deprivation) followed by reperfusion (reoxygenation + substrate replacement) on the contractile response of rabbit urinary bladder strips to nonrepetitive and repetitive field stimulation (FS), and correlated the results with the rate of lipid peroxidation. We view repetitive FS as a model for hyperreflexia. Methods: The effects of repetitive and nonrepetitive FS on the contractile responses of isolated strips of rabbit bladder to FS, carbachol, and KCl were determined in the presence of 3 different incubation media: O₂ + glucose (normal physiological medium); N₂ + glucose (in vitro hypoxia), and N₂ – glucose (in vitro ischemia). Then, all strips were incubated for 1 h in normal physiological medium (‘reperfusion’) followed by a final stimulation; the resultant contractile responses were correlated with the level of lipid peroxidation as determined by malonedialdehyde (MDA) concentration. Results: Repetitive stimulation, a model of hyperreflexia, significantly increased the rate of development of contractile dysfunction in bladder tissue strips incubated in all 3 media as compared to nonrepetitive stimulation, which caused no degradation of the contractile response in normal physiological medium. The rate of development of contractile dysfunction was significantly greater in bladder tissue strips incubated in the in vitro ischemia medium (N₂ – glucose) than in strips incubated in the hypoxia medium (N₂ + glucose); which, in turn, was significantly greater than in those incubated in the normal physiological medium (O₂ + glucose). Repetitive stimulation (‘hyperreflexia’) during all 3 incubation conditions resulted in increased [MDA] after reoxygenation or ‘reperfusion’. Incubation in in vitro ischemia buffer (N₂ – glucose) followed by 1 h reoxygenation + substrate replacement stimulated lipid peroxidation to a significantly greater extent than did incubation in hypoxia buffer (N₂ + glucose) followed by 1 h of reoxygenation; the level of lipid peroxidation, [MDA], paralleled the magnitude of the contractile dysfunctions present. Independent of the incubation medium, the magnitude of FS-induced contractile dysfunction after reoxygenation or ‘reperfusion’ was significantly greater than the magnitude of dysfunction in response to carbachol or KCl. Conclusions: The results demonstrate that the rate of contractile failure induced by in vitro ischemia is greater than that induced by in vitro hypoxia, and that the contractile response to FS is significantly more sensitive to both hypoxia and in vitro ischemia than is the contractile response to either carbachol or KCl. Repetitive stimulation (‘hyperreflexia’) increases the rate of contractile failure under all conditions tested, and the magnitude of the contractile failure may be due, in part, to the generation of free radicals and subsequent stimulation ...

The use of Hypochlorous Acid as a Model for Investigating Bladder Overactivity

“…Experimental studies that have examined the association between oxidative stress and bladder dysfunction have supported the hypothesis that the generation of free radicals might be linked to bladder dysfunction (9)(10)(11). Possibly, the detrusor dysfunction is caused by activation of specific hydrolytic enzymes including calpain and phospholipase A 2 with subsequent damage to intracellular organelles such as the mitochondria and sarcoplasmic reticulum and via generation of reactive oxygen species and subsequent membrane lipid peroxidation (12,13).…”

Effect of Co-enzyme Q10 and Alpha-Lipoic Acid on Response of Rabbit Urinary Bladder to Repetitive Stimulation and In Vitro Ischemia

“…6 The time courses of the effect of repetitive stimulation in the presence and absence of both glucose deprivation and in vitro ishchemia have been published previously. 19,20 The aim of the current study was to investigate whether CoQ10,α-LA, or the combination can protect against the contractile dysfunctions induced by repetitive stimulation in the presence or absence of in vitro ischemia.…”

Influence of oxidative stress on inducing micturition dysfunction following chronic infravesical obstruction and the protective role of an antioxidant diet - association of in vivo and in vitro studies in rats

“…Recently, experimental studies have demonstrated a positive association between the triggering of OBS and the generation of free radicals (4,5). The results from an experimental study involving smooth muscle fragments subjected to periods of repeated electrical stimulation demonstrated high levels of lipid peroxidation products, and decreased smooth muscle contractility of the bladder, proportional to the level of oxidative stress (4).…”

“…The results from an experimental study involving smooth muscle fragments subjected to periods of repeated electrical stimulation demonstrated high levels of lipid peroxidation products, and decreased smooth muscle contractility of the bladder, proportional to the level of oxidative stress (4). Masick et al (5) demonstrated the existence of deterioration in muscle contraction, and also the emergence of oxygen-reactive species, in the bladders of animals subjected to chronic urethral obstruction.…”