The mode of action of prostaglandin E2, F2 alpha and prostacyclin on vesicourethral smooth muscle

Prostaglandin D2 effects and DP1 /DP2 receptor distribution in guinea pig urinary bladder out-flow region

The proximal urethra and urinary bladder trigone play important roles in continence. We have previously shown that PGD₂ is released from guinea pig bladder urothelium/suburothelium and can inhibit detrusor contractile responses. We presently wished to investigate PGD₂ actions in guinea pig out‐flow region and the distribution of DP₁/DP₂ receptors. The effects of PGD₂ on urothelium‐intact trigone and proximal urethra contractility were studied in organ bath experiments. Expression of DP₁/DP₂ receptor proteins was analysed by western blot. Immunohistochemistry was used to identify distribution of DP₁/DP₂ receptors. PGD₂ in a dose‐dependent manner inhibited trigone contractions induced by electrical field stimulation (EFS) and inhibited spontaneous contractions of the proximal urethra. PGD₂ was equally (trigone) or slightly less potent (urethra) compared with PGE₂. Expression of DP₁ and DP₂ receptors was found in male guinea pig bladder trigone, neck and proximal urethra. In the trigone and proximal urethra, DP₁ receptors were found on the membrane of smooth muscle cells and weak immunoreactivty was observed in the urothelium. DP₂ receptors were distributed more widespread, weakly and evenly in the urothelium and smooth muscles. Inhibitory effects by PGD₂ on motor activity of guinea pig trigone and proximal urethra are consistent with finding DP₁ and DP₂ receptors located in the urothelium and smooth muscle cells of the trigone and proximal urethra, and PGD₂ may therefore be a modulator of the bladder out‐flow region, possibly having a function in regulation of micturition and a role in overactive bladder syndrome.

Latanoprost-related transient incontinence

Latanoprost has increasingly become the first choice in topical anti-glaucoma therapy. Local adverse events like hypertrichosis and increased iris pigmentation are common whereas systemic adverse events have been rare and mild in intensity. The authors would like to report a case of transient urge incontinence after initiation of latanoprost therapy confirmed by challenge-rechallenge tests and speculate on the causal relationship.

Prostaglandin E2 release from isolated bladder strips in rats with spinal cord injury

AIM

Recent studies have shown that various factors contribute to the increased excitability into the bladder afferent nerves in spinal cord injury (SCI) rats. It has been reported that prostaglandins (PG) act as local modulators of reflex micturition in pathological conditions. In the present study, we measured the amount of PGE2 release from the bladder of chronic SCI rats.

METHODS

Spinal cord was transected at the level of T8-9 in adult female Sprague-Dawley rats. After 10 weeks, specimens of the urinary bladder were obtained from SCI rats and sham-injured control rats, and bladder strips were dissected from the bladder. Using an muscle-bath technique and a microdialysis procedure, the dialysate, containing substance released from bladder strips, was collected. Then the amount of PGE2 in the dialysate was measured by radioimmunoassay.

RESULTS

Excretion of urinary PGE2 was significantly higher in SCI rats than in control rats. PGE2 release from bladder strips was significantly higher in SCI rats than in control rats. Removal of urothelium caused significant decreases in PGE2 release in both control and SCI rats. Stretches of the bladder strips caused significant resting tension-dependent increases in PGE2 release from the strips with urothelium.

CONCLUSIONS

The present data suggest that bladder urothelium partly contributes to the increase in PGE2 release from the bladder, and that bladder distension may cause increases in PGE2 release in SCI rats.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Role of prostaglandins in the urinary bladder: an update

Our knowledge of prostanoids is rapidly increasing. In this review we survey the factors governing the synthesis of prostanoids by the urinary bladder, their role in the maintenance of normal bladder function, the pattern of their secretion in bladder disease and the possible use of prostanoids in the treatment of bladder pathology.

The effect of SC-19220, a prostaglandin antagonist, on the micturition reflex in rats

SC-19220 (5-20 mg/kg i.v.), a competitive receptor antagonist of PGE, increased the bladder capacity and reduced the voiding efficiency of micturition (elicited by slow transvesical filling) of urethane-anesthetized rats. The effect of SC-19220 was prevented by indomethacin pretreatment, whereas indomethacin per se mimicked the effects of SC-19220. SC-19220 produced a competitive rightward shift of the dose-response curve for the contractile effect induced by PGE2 on strips of rat detrusor muscle in vitro, whereas the amplitude of nerve-mediated twitches was unaffected. These findings support the hypothesis that endogenous PGE2 is physiologically involved in the regulation of vesicourethral motility in this species by facilitating attainment of the micturition threshold during the collection phase of the cystometrogram.

Regulation of prostaglandin synthesis by reduced glutathione in urinary bladder epithelium

A possible mechanism is presented by which reduced glutathione (GSH) regulates prostaglandin (PG) synthesis in microsomes of the porcine bladder epithelium. At a concentration of GSH less than 10(-5) M, microsomes produced more PGI2 and PGF2 alpha than PGE2. At a greater GSH concentration, PGE2 synthesis was remarkably enhanced. On the other hand, PGI2 and PGF2 alpha synthesis was inhibited. In the presence of 10(-3) M GSH, ten times more PGE2 was produced than the other PGs. The concentration of GSH in porcine bladder epithelium was about 0.6 mM. This reciprocal effect of GSH was also observed in rabbit and bovine bladder epithelium. These findings suggest that GSH is involved in the regulation of PG synthesis in urinary bladder epithelium. GSH may influence the physiological and pathophysiological changes elicited by PGs in the lower urinary tract.

Prostanoids modulate reflex micturition by acting through capsaicin-sensitive afferents

Topical application of exogenous prostanoids (PGE2, TBX B2) on the serosal surface of the urinary bladder of urethane-anaesthetized rats activated reflex micturition. Likewise, intravesical instillation of PGE2 during the cystometrogram lowered the threshold for reflex micturition. Both effects were prevented by systemic capsaicin desensitization (50 mg/kg s.c., 4 days before). Indomethacin pretreatment and systemic capsaicin desensitization each increased the micturition threshold without affecting the amplitude of micturition contraction. However, the effect of the two treatments combined was not greater than the effect of either alone. These findings support the idea that endogenous prostanoids facilitate reflex micturition by stimulating or sensitizing, directly or indirectly, the subset of bladder mechanoreceptors which is capsaicin-sensitive in adult rats.

Urinary bladder prostanoids--their synthesis, function and possible role in the pathogenesis and treatment of disease

The present review surveys the factors governing the synthesis of prostanoids by the urinary bladder, their role in the maintenance of normal bladder function, the pattern of their secretion in bladder disease and, finally, their possible use in the treatment of bladder pathology. It should be emphasized that this area of investigation is in its infancy, and therefore the pathophysiological and clinical relevance of these observations is, to some extent, speculative. However, a certain degree of awareness is necessary to stimulate further studies in this promising field of research.