Study on Physiological Roles of Stimulation of Prostaglandin E2 Receptor Subtype EP2 in Urethral Function in Rats

PGE2 binding to EP2 promotes ureteral stone expulsion by relaxing ureter via the cAMP-PKA pathway

BACKGROUND

This study investigated the relaxation effect of PGE2 on the ureter and its role in promoting calculi expulsion following calculi development.

METHODS

By using immunofluorescence and Western blot, we were able to locate EP receptors in the ureter. In vitro experiments assessed the impact of PGE2, receptor antagonists, and agonists on ureteral relaxation rate. We constructed a model of ureteral calculi with flowable resin and collected ureteral tissue from postoperative side of the ureter after obstruction surgery. Western blot analysis was used to determine the protein expression levels of EP receptors and the PGE2 terminal synthase mPGES-1. Additionally, PGE2 was added to smooth muscle cells to observe downstream cAMP and PKA changes.

RESULTS

The expression of EP2 and EP4 proteins in ureteral smooth muscle was verified by Western blot analysis. According to immunofluorescence, EP2 was primarily found on the cell membrane, while EP4 was found in the nucleus. In vitro, PGE2 induced concentration-dependent ureteral relaxation. Maximum diastolic rate was 70.94 ± 4.57% at a concentration of 30µM. EP2 antagonists hindered this effect, while EP4 antagonists did not. Obstructed ureters exhibited elevated mPGES-1 and EP2 protein expression (P < 0.01). Smooth muscle cells treated with PGE2 displayed increased cAMP and phosphorylated PKA.

CONCLUSIONS

PGE2 binding to EP2 induces ureteral relaxation through the cAMP-PKA pathway. This will provide a new theoretical basis for the development of new therapeutic approaches for the use of PGE2 in the treatment of ureteral stones.

Lipopolysaccharide reduces urethral smooth muscle contractility via cyclooxygenase activation

Lipopolysaccharide (LPS) is a component of gram-negative bacteria wall that elicits inflammatory response in the host through the toll-like receptor 4 (TLR4) activation. In the lower urinary tract (LUT), bacteria-derived LPS has been associated with lower urinary tract symptoms (LUTS); however, little is known about the effects of LPS in the urethral smooth muscle (USM). In the present study, we evaluated the functional and molecular effects of LPS in mouse USM in vitro, focusing on the LPS-induced TLR4-signaling pathway. Male C57BL6/JUnib and TLR4 knockout mice (TLR4 KO) were used. The USM contraction was performed in the presence of LPS (62.5-500 μg/mL), indomethacin (10 μM), L-NAME (100 μM), and TAK 242 (1 μM). The RT-PCR assay for the IL-1β, NF-kB, and COX-2 genes was also evaluated in the presence of LPS (125 μg/mL) and caspase 1 inhibitor (20 μM). Our results showed that LPS reduces mouse USM contraction elicited by phenylephrine and vasopressin. This LPS-induced urethral inhibitory effect was not reversed by the TLR4 inhibition or its absence in the TLR4 KO mice. Conversely, indomethacin (but not L-NAME) reversed the LPS-induced USM hypocontractility. Molecular protocols indicated upregulation of IL-1β, NF-kβ, and COX-2 mRNA upon LPS incubation, which were blunted by caspase 1 inhibition. Our data showed that LPS reduced mouse USM contraction independently of TLR4 activation, involving caspase 1 and IL1β, NF-kB, and COX-2 gene overexpression. Therefore, this alternative pathway might be a valuable target to reduce the LPS-induced urethral dysfunction under infection and inflammatory conditions.

Effects of intravesical prostaglandin E2 on bladder function are preserved in capsaicin-desensitized rats

Prostaglandin E2 (PGE2) instilled into the bladder generates symptoms of urinary urgency in healthy women and reduces bladder capacity and urethral pressure in both humans and female rats. Systemic capsaicin desensitization, which causes degeneration of C-fibers, prevented PGE2-mediated reductions in bladder capacity, suggesting that PGE2 acts as an irritant (Maggi CA, Giuliani S, Conte B, Furio M, Santicioli P, Meli P, Gragnani L, Meli A. Eur J Pharmacol 145: 105-112, 1988). In the present study, we instilled PGE2 in female rats after capsaicin desensitization but without the hypogastric nerve transection that was conducted in the Maggi et al. study. One week after capsaicin injection (125 mg/kg sc), rats underwent cystometric and urethral perfusion testing under urethane anesthesia with saline and 100 µM PGE2. Similar to naïve rats, capsaicin-desensitized rats exhibited a reduction in bladder capacity from 1.23 ± 0.08 mL to 0.70 ± 0.10 mL (P = 0.002, n = 9), a reduction in urethral perfusion pressure from 19.3 ± 2.1 cmH2O to 10.9 ± 1.2 cmH2O (P = 0.004, n = 9), and a reduction in bladder compliance from 0.13 ± 0.020 mL/cmH2O to 0.090 ± 0.014 mL/cmH2O (P = 0.011, n = 9). Thus, changes in bladder function following the instillation of PGE2 were not dependent on capsaicin-sensitive pathways. Further, these results suggest that urethral relaxation/weakness and/or increased detrusor pressure as a result of decreased compliance may contribute to urinary urgency and highlight potential targets for new therapies for overactive bladder.

Further characterization of a novel EP2 and EP3 receptor dual agonist, ONO-8055, on lower urinary tract function in normal and lumbar canal stenosis rats

AIMS

To further explore the effects of a novel EP2 and EP3 dual agonist, ONO-8055, on detrusor contractility, we investigated the responses of bladder strips from sham and lumbar canal stenosis (LCS) rats to this agonist, its effects on lower urinary tract function in normal rats, and mRNA expression of EP2 and EP3 receptors in the sham and LCS rats.

METHODS

The responses of bladder strips from sham and LCS rats to ONO-8055 were measured. The effects of ONO-8055 on LUT function of normal rats were investigated with awake cystometry and intraurethral perfusion pressure (Pura) measurements. The relative mRNA of bladder and urethral tissue of the sham and LCS rats was quantified using specific probes for EP1, EP2, EP3, and EP4 genes.

RESULTS

Compared with the vehicle, the muscle tensions of both the sham and LCS rats were significantly increased after adding this agonist. On awake cystometry of normal rats, bladder capacity and Pura were decreased in the ONO-8055 groups, but a statistically significant difference in mean changes was demonstrated only between the vehicle group and the group receiving the highest dose. Compared with the sham rats, mRNA expressions of the four EP receptors in the lower urinary tract of the LCS rats did not show a statistically significant difference.

CONCLUSIONS

This agonist did not augment bladder contractility or urethral relaxation in normal rats.

High luteinizing hormone weakens urinary continence mechanisms in association with prostaglandin E2 elevation in a postmenopausal rat model

AIMS

To explore the role of luteinizing hormone (LH) in the urinary continence mechanism, urethral function was investigated using a postmenopausal rat model with high serum LH concentrations and the postmenopausal rat model given a gonadotropin releasing hormone (GnRH) antagonist to lower LH concentrations.

METHODS

Adult female rats were divided into: 1) sham group; 2) ovariectomy group (OVX) with removal of bilateral ovaries; 3) OVX and GnRH-antagonist administered group (OVX + G); and 4) sham and GnRH-antagonist administered group (Sham + G). Urethral function was evaluated by the sneeze-induced urethral continence reflex experiment, and serum LH and prostaglandin E2 (PGE2) concentrations were measured.

RESULTS

In the sneeze-induced urethral continence reflex experiment, urethral baseline pressure (UBP) and the amplitude of the urethral response during sneezing (A-URS) were measured. The UBP was significantly decreased in the OVX group than in the other groups. A-URS was significantly lower in the OVX group than in the Sham group, but with no significant difference compared with the OVX + G group. Lowering the serum LH by a GnRH-antagonist improved UBP to the same level as in the Sham group. The serum PGE2 concentration was significantly higher in the OVX group than in the other groups.

CONCLUSIONS

The results suggested that the increased serum LH concentration in the OVX rat model worsened the continence mechanism. This mechanism is probably associated with an increased PGE2 concentration, because PGE2 caused urethral smooth muscle relaxation. A GnRH-antagonist might improve urinary incontinence by decreasing the serum LH and PGE2 concentrations.

Urethral function and histopathology in aged female rats as a stress urinary incontinence model

OBJECTIVE

Stress urinary incontinence (SUI) is a common disease condition in elderly women, suggesting that its etiology may be linked to aging. To investigate the hypothesis that urethral dysfunction and histopathological changes are possible contributors to SUI in elderly women, several parameters of urethral function, as well as histological parameters, were compared between young and aged rats.

METHODS

Virgin female rats were examined at 3 different ages, namely 3, 12, and 24 months, corresponding to young, middle-aged, and aged rats, respectively. Urethral function was assessed by measuring the leak point pressure (LPP), pudendal nerve stimulation (PNS)-induced elevation in urethral pressure, and phenylephrine-induced increase in urethral perfusion pressure (UPP). Histopathological assessments were performed following hematoxylin and eosin (HE), Masson's trichrome, and immunofluorescence staining of urethral tissue.

RESULTS

LPP of aged rats was significantly reduced compared to that of both young and middle-aged rats. PNS-induced elevation in urethral pressure in aged rats was also significantly lower than that in young rats. In contrast, there were no significant differences in the phenylephrine-induced increase in UPP between young and aged rats. Connective tissue area in the external urethral sphincter (EUS) layer was increased in aged rats, whereas the smooth muscle layer was histologically similar to that in young rats. The number of EUS fibers was significantly reduced in aged rats, whereas the cross-sectional area of EUS fibers increased from differed compared with young rats.

CONCLUSION

We have demonstrated age-related changes in EUS function and morphology in the rat urethra, which are considered to be etiological risk factors for SUI in humans.

OAB without an overactive bladder in the acute prostaglandin E2 rat model

Intravesical prostaglandin E2 (PGE2) was previously used to induce overactive bladder (OAB) symptoms, as it reduces bladder capacity in rats and causes a "strong urgency sensation" in healthy women. However, the mechanism by which this occurs is unclear. To clarify how PGE2 reduces bladder capacity, 100 µM PGE2 was administered intravesically during open, single-fill cystometry with simultaneous measurement of sphincter EMG in the urethane-anesthetized female Wistar rat. PGE2 was also applied to the urethra or bladder selectively by use of a ligature at the bladder neck before (urethra) or during (bladder) closed-outlet, single-fill cystometry. Additional tests of urethral perfusion with PGE2 were made. PGE2 decreased bladder capacity, increased voiding efficiency, and increased sphincter EMG during open cystometry compared with saline controls. The number of nonvoiding contractions did not change with PGE2; however, bladder compliance decreased. During closed-outlet cystometry, PGE2 applied only to the bladder or the urethra did not decrease bladder capacity. Urethral infusion of PGE2 decreased urethral perfusion pressure. Taken together, these results suggest that intravesical PGE2 may decrease bladder capacity by targeting afferents in the proximal urethra. This may occur through urethral relaxation and decreased bladder compliance, both of which may increase activation of proximal urethra afferents from distension of the proximal urethra. This hypothesis stands in contrast to many hypotheses of urgency that focus on bladder dysfunction as the primary cause of OAB symptoms. Targeting the urethra, particularly urethral smooth muscle, may be a promising avenue for the design of drugs and devices to treat OAB.

Effect of Selective Prostaglandin E2 EP2 Receptor Agonist CP-533,536 on Voiding Efficiency in Rats with Midodrine-Induced Functional Urethral Obstruction

OBJECTIVES

We investigated the effect of the selective prostaglandin E2 EP2 receptor agonist CP-533,536 on voiding efficiency in rats with midodrine-induced functional urethral obstruction.

METHODS

The effect of CP-533,536 (0.03-0.3 mg/kg, intravenous [i.v.]) on urethral perfusion pressure (UPP) was investigated in anesthetized rats pre-treated with midodrine (1 mg/kg, i.v.), which forms an active metabolite that acts as an α1 -adrenoceptor agonist. The effect of CP-533,536 (0.03-0.3 mg/kg, i.v.) on cystometric parameters was also investigated in anesthetized rats. In addition, the effect of CP-533,536 (0.03-0.3 mg/kg, i.v.) on residual urine volume (RV) and voiding efficiency (VE) was investigated in conscious rats treated with midodrine (1 mg/kg, i.v.).

RESULTS

CP-533,536 dose-dependently decreased UPP elevated by midodrine in anesthetized rats. In contrast, CP-533,536 did not affect maximum voiding pressure, intercontraction interval, or intravesical threshold pressure. In conscious rats, midodrine (1 mg/kg, i.v.) markedly increased RV and reduced VE. CP-533,536 dose-dependently ameliorated increases in RV and decreases in VE induced by midodrine.

CONCLUSIONS

These results suggest that a selective EP2 receptor agonist could ameliorate the elevation of RV and improve the reduction of VE in rats with functional urethral obstruction caused by stimulation of α1 -adrenoceptors. The mechanism of action might be not potentiation of bladder contraction but rather preferential relief of urethral constriction.