Inhibitory Effects of Urothelium-related Factors

The urothelium of the bladder has long been recognized as a protective barrier between detrusor and urine. In recent years, it has become more evident that the urothelium plays a role as an active source of mediators. The urothelium can release neurotransmitters and modulators such as acetylcholine, ATP, nitric oxide, prostaglandins and neuropeptides. They exert both excitatory and inhibitory effects in modulating urinary tract motility. In addition, several studies have reported the existence of an urothelium-derived unknown inhibitory factor in the urinary bladder. By the use of a new serial cascade superfusion bioassay on guinea pig ureter, recent studies confirm that the guinea pig bladder urothelium releases a substance with inhibitory bioactivity, which was resistant to treatment with nitric oxide synthase inhibitor and cyclooxygenase inhibitor and to adenosine A1/A2 receptor blockade. Lately, a marked and quickly inactivated novel release of PGD₂ from the bladder urothelium was discovered, together with localization of prostaglandin D synthase therein. PGD₂ was found to have an inhibitory influence on nerve-induced contractions in guinea pig urinary bladder and on spontaneous contractions in the out-flow region. An altered release of excitatory and inhibitory factors is likely to play an important part in bladder motility disturbances, of which the prostanoids are a notable group. Due to the fact that the bladder is relaxed 99% of the time, not only excitatory mechanisms in the bladder are necessary to study, but also inhibitory mechanisms need considerable attention, which will contribute to the discovery of new targets to treat bladder motility disorders.