Expression of E-series prostaglandin (EP) receptors and urodynamic effects of an EP4 receptor antagonist on cyclophosphamide-induced overactive bladder in rats

Abstract

Objective: To investigate the expression of four subtypes of E-series prostaglandin (EP(1) -EP(4) ) receptors and the urodynamic effects of an EP(4) receptor antagonist (AH23848) in cyclophosphamide (CYP)-induced overactive bladder (OAB) in rats, as intravesical prostaglandin E(2) (PGE(2) ) induces OAB via activation of EP receptors and sensitization of afferent nerves.

Materials and methods: Experimental and control rats were injected with CYP (200 mg/kg, intraperitoneally) or saline, respectively. Continuous cystometrograms (CMGs) were performed 48 h after CYP or saline injection under urethane anaesthesia. AH23848 was given intravenously at doses of 0.01 and 0.1 mg/kg. The bladder was then harvested for histology. Some bladders were harvested for analysis of EP receptors expression by Western blotting without a CMG study. CMG variables (baseline pressure; intercontraction interval [ICI], pressure threshold [PT], contraction amplitude) and histological changes were measured.

Results: CYP-induced up-regulation of EP(4) receptor (100% increase) accompanied by detrusor overactivity (ICI 70.5% decrease; PT, 67.7% increase). However, CYP down-regulated EP(1) receptor expression (51.9% decrease), but had no significant effects on the EP(2) and EP(3) receptors. AH23848 significantly extended the ICI in CYP-treated rats but it had no effects on other urodynamic variables or in control rats.

Conclusions: Modulation of EP receptors plays a role in CYP-induced OAB. Antagonists to the EP(4) receptor may be a new target for treatment of patients with OAB.

FIG. 1

A, Gross view, on day 3, CYP significantly induced swelling and haemorrhage of bladder (left) compared with the control rat (right). B, Western blotting for detecting EP receptors expression in the bladder of saline- (right) and CYP- (left) treated rats. CYP induced up-regulation of EP₄ receptor accompanied by down-regulation of EP₁ receptor. However, CYP had no significant effects on EP₂ and EP₃ receptors.

FIG. 2

Representative traces of in vivo continuous CMGs in urethane-anaesthetized rats. CMG was performed in a control rat (A) with a normal voiding pattern and in a rat with CYP-induced OAB (B) before and after i.v. administration of AH23848 (0.01 and 0.1 mg/kg; i.v).

FIG. 3

Photomicrographs of bladder sections. Control rat with intact urothelium (A,B) and rare EP₄ immunostaining (C); CYP-induced inflammatory cells accumulation, oedematous change, haemorrhage of urothelium (D,E) and up-regulation of EP₄ expression (F) at urothelium (arrow), inflammatory cells (white arrow head), and macrophage (black arrow head). A, D ×40; B, C, E, F ×200.