Bladder Outlet Obstruction Induced Expression of Prostaglandin E 2 Receptor Subtype EP4 in the Rat Bladder: A Possible Counteractive Mechanism Against Detrusor Overactivity

Abstract

Prostaglandins have been implicated as endogenous modulators of bladder function under physiological and pathological conditions. We examined how the expression of each EP receptor subtype changed in association with bladder outlet obstruction and focused on the functional role of EP4 receptor subtype in the bladder with outlet obstruction. We assessed the gene expression of EP receptor subtypes by reverse transcriptase-polymerase chain reaction. EP4 protein localization was determined by immunohistochemistry. The effect of the selective EP4 agonist ONO-AE1-329 on 50 mM KCl induced contraction of rat bladder strips was examined in vitro. Continuous infusion cystometrograms were done to examine the effect of intravesical perfusion of ONO-AE1-329 on the micturition reflex in urethane anesthetized rats. EP4 receptor genes were largely expressed in bladders with outlet obstruction but absent in controls. EP4 receptor proteins were clearly detected in obstructed bladder detrusor smooth muscle and epithelium. ONO-AE1-329 (100 μM) significantly relaxed KCl induced contraction of bladder strips from rats with bladder outlet obstruction. A significant correlation was found between the relaxant effect of ONO-AE1-329 and whole bladder weight. In rats with bladder outlet obstruction intravesical infusion of 10 μM ONO-AE1-329 significantly increased bladder capacity without changing micturition pressure while it had no effect in controls. Activation of the EP4 receptors expressed in bladders with outlet obstruction may suppress detrusor muscle contraction and afferent activity. This might be a compensatory mechanism to counteract the deterioration of storage function in bladders with outlet obstruction.