The effect of in vitro ischemia/reperfusion on contraction, free fatty acid content, phospholipid content, and malondialdehyde levels of the rabbit urinary bladder

Abstract

To evaluate the effects of in vitro ischemia/reperfusion on contractile response to field stimulation (FS), free fatty acid (FFA) content, phospholipid (PL) content, and malondialdehyde (MDA) levels of the rabbit urinary bladder. There is significant evidence that ischemia/reperfusion injury is linked to obstructive bladder dysfunction secondary to men with benign prostatic hyperplasia (BPH). Twelve New Zealand White male rabbits were separated into two groups of six rabbits each. Each rabbit was euthanized, and the bladder was surgically removed intact for whole bladder incubation. The bladders in Group 1 received a 3-h incubation under normal oxygenated physiological conditions. These bladders received electrical field stimulation (32Hz) after 1 and 3h. The bladders associated with Group 2 received a 1-h incubation under normal oxygenated physiological conditions. At the end of this 1-h period, the bladders were subjected to FS. After a maximal pressure response was recorded, the stimulation was turned off and the bath medium was changed to one equilibrated with 95% nitrogen, 5% oxygen without glucose (ischemic medium) and incubated for 1h with field stimulations (32Hz) occurring at 5-min intervals to represent overactive bladder dysfunction. At the end of this hour of ischemia with repetitive stimulation, the bath was changed to an oxygenated medium with glucose for a 1-h period after which the stimulation was repeated. At the end of the experimental period, each bladder was opened longitudinally and the muscle and mucosa separated by blunt dissection, frozen under liquid nitrogen, and stored at -80°C for biochemical analyses. Each tissue was fractionated by differential centrifugation into nuclear, mitochondrial, synaptosomal, and supernatant (cytosol) components. PL, FFA, and MDA content were analyzed for each fraction using standard biochemical techniques. The bladder contractile responses decreased during the period of in vitro ischemia and returned to only 30% of control after reperfusion. In vitro ischemia/reperfusion showed the following: (1) There was a modest but significant decrease in the FFA content of the microsomes of the muscle and significant increases in the FFA content of the nuclei and mitochondria of the mucosa. (2) There were decreases in the PL content of the homogenate and microsomes of the muscle and decreases in the PL content of the homogenate, microsomes, and supernatant of the mucosa. (3) Significant increases were observed in the MDA levels of the homogenate, mitochondria, and microsomes of both the muscle and mucosa. The significant increases in the lipid peroxidation of the bladder smooth muscle are consistent with the marked decrease in the contractile ability of the bladder following ischemia/reperfusion. The specific increased lipid peroxidation of the mitochondrial and microsomal components is consistent with the specific dysfunctions of the mitochondria and innervations observed following I/R in earlier published studies. The marked increases in lipid peroxidation in the mucosa associated with the loss of PL and FFA from this component are consistent with the significant dysfunction in both the antiadherence and antipermeability properties of the mucosa and may play a major role in the symptomatic nature of I/R-linked diseases of the bladder.