The protective effect of oxytocin on ischemia/reperfusion injury in rat urinary bladder

Abstract

Oxytocin (OXY), a well-known nonapeptide, plays a crucial role in reproduction, and has effects on modulating the immune and inflammatory processes in living organisms as well. Recently it is also known as an antioxidant in several organs. The present study aims to demonstrate the protective effect of OXY against ischemia/reperfusion (I/R) injury in urinary bladder tissue. Abdominal aorta of rats, were clamped to perform urinary bladder ischemia. OXY (0.5 μg/kg) was injected intraperitoneally before ischemia in I/R + OXY group, whereas the vehicle solution was injected to I/R group. At the end of reperfusion, tissue samples from urinary bladder were processed for histochemical, ultrastructural and biochemical analysis. Tissue sections were stained by toluidine blue for mast cell counting and hematoxylin–eosin for histopathology. In addition, malondialdehyde (MDA) and glutathione (GSH) levels were determined biochemically. The results demonstrated that there was an extreme damage at urothelium, dilatation of intercellular junctions, inflammatory cell infiltration in I/R group. I/R + OXY group demonstrated a reduction in the severity of urinary bladder damage. According to mast cell counting results, both granulated and degranulated mast cells were decreased in I/R + OXY group compared to I/R group. The mean MDA level was higher in I/R group compared to control and lower in I/R + OXY group compared to I/R group. GSH level reduced in I/R group compared to the control and increased in I/R + OXY group compared to I/R group. In conclusion, oxytocin, as confirmed by histological evaluation and biochemical assays has a potential protective effect in the urinary bladder tissue against ischemia/reperfusion injury.

Introduction

In clinical practice, hypoperfusion of the urinary bladder can result from ischemia during shock and trauma, or from different local events caused by embolism, thrombophlebitis, ligation, complication of pregnancy or pelvic surgery, compression by pelvic tumors or from over-distension of the bladder caused by lower urinary tract obstruction [5].

Ischemia/reperfusion (I/R) injuries result in damage to endothelial and parenchymal cells, accompanied by reactions of granulocytes and macrophages as well as humoral factors, including complement, coagulation factors, free radicals, and nitric oxide [27], [28]. I/R can activate macrophages and plays a role in release of cytokines which triggers leukocyte activation, transmigration, and target cell adhesion [28]. The enormous number of leukocytes that enter the extravascular space immediately after reperfusion, results in releasing of large quantities of reactive oxygen species (ROS), capable of depressing the cellular defence provided by antioxidants [18], [22]. Some ROS are hydroxyl radical (OH), superoxide anion radical (O₂⁻), singlet oxygen (1O₂), hydrogen peroxide (H₂O₂) and nitric oxide (NO⁻), which cause damage to lipids, proteins, carbohydrates and nucleic acids, and thus leads to cellular injury [8], [9], [30]. ROS affect the polyunsaturated fatty acids in the membrane lipids, thereby lipid peroxidation results in loss of membrane integrity. This is followed by rupture of plasma membrane, and eventually leads to cell death [31]. Oxidative stress is an alteration in the balance of free radicals and the antioxidant enzymes in the cells and body system [12].

The severity of I/R injury depends both on duration of ischemia and subsequent reperfusion periods. Reperfusion, although essential for the survival of ischemic tissue, causes additional damage [10]. Acute ischemia leads to the activation of endothelium by an increase in permeability and expression of different adhesion molecules [14], and evokes an acute inflammatory response characterized by activation of neutrophils [16]. The activated neutrophils induce tissue injury through production and release of reactive oxygen metabolites and cytotoxic proteins into the extracellular fluid [25], which constitutes inflammatory cascades that lead to the radical-induced I/R injury [35].

Oxytocin (OXY), a nonapeptide, produced in the paraventricular and supraoptical nuclei in the hypothalamus, plays an important role in central and peripheral effects. OXY mediates uterine contraction during parturition and milk ejection reflex during lactation. It is also effective in cardiovascular and hydroelectrolytic regulations, modulation of various behaviors such as maternal, social and sexual behaviors, as well as release of adenohypophyseal hormones [19]. OXY receptors have also been presented in other tissues, such as, heart, thymus, pancreas and adipocytes [13]. It has been recently revealed that OXY is able to trigger wound healing and to modulate the immune and inflammatory processes. These effects could be explained by the presence of OXY and OXY receptors in the thymus, and these elements act as acute phase reactants and interleukins [26]. It was found that OXY may decrease the release of some interleukins and increase the survival of ischemic skin flaps in rats via the activation of the growth factors or anti-inflammatory mechanisms [32].

Many studies showed the importance of ischemia/reperfusion in the pathophysiology of genitourinary tract [3], [7], [33], [34]. However, there are no studies concerning the protective effects of oxytocin on I/R injury in urinary bladder. The goal of this study was to evaluate the protective effect of an antioxidant, oxytocin, against ischemia and reperfusion on the injured tissue of urinary bladder by microscopical and biochemical analysis.