Nitric oxide and the cyclic nucleotide monophosphates cAMP and cGMP have a role in control of the micturition process and hence, are suggested to be involved in the pathophysiology of storage and voiding disorders. Phosphodiesterase enzymes (PDEs) hydrolyse cAMP and cGMP. Inhibition of PDEs increases cAMP and cGMP levels and relaxes urinary bladder smooth musculature. Although many preclinical studies have been conducted, to date, only PDE1 and PDE5 inhibitors have been tested clinically for the management of storage and voiding disorders. Treatment with PDE1 inhibitors might improve micturition frequency in patients with overactive bladder, whereas inhibition of PDE5 improves lower urinary tract symptoms in men, either with or without BPH and erectile dysfunction (ED). Furthermore, the combination of a PDE5 inhibitor and an α-adrenoceptor antagonist has superior efficacy to monotherapy with either agent. However, the role of PDE5 inhibitors in the treatment of women with detrusor overactivity remains unclear. The clinical application of agents that inhibit other PDEs, including PDE4, also certainly merits scientific attention. PDE inhibitors seem likely to become a valuable alternative treatment for patients with storage and voiding disorders in the future.

Objective• To study PDE5 localisation by visualising the product of phosphodiesterase type 5 (PDE5) inhibition, namely cGMP, to determine the site of action of inhibitors in the urinary bladder. Materials and Methods• Bladders of nine male guinea pigs were dissected and treated in wells containing 2 mL Krebs' solution and 1 mM of the specific PDE5 inhibitor vardenafil at 36°C for 30 min. • After stimulating tissues with 100 mM of the nitric oxide (NO) donor diethylamine-NONOate for 10 min, the tissues were snap-frozen and 9-10 mm sections were cut. • Sections were examined for cGMP immunoreactivity and also stained for vimentin, a marker for interstitial cells and the neuromarkers protein gene product 9.5 (PGP9.5), synaptic vesicle protein 2 (SV2), neurofilament (NF) and calcitonin gene-related peptide (CGRP), using the two-step indirect immunohistochemistry technique. Results• After PDE5 inhibition, cGMP was found to be present in the urothelium, suburothelial interstitial cells and endothelium of blood vessels.• cGMP was not expressed in nerves positive for CGRP, NF and SV2, and was expressed only in very few efferent nerves positive for PGP9.5. Conclusion• Our data show that the possible sites of action of PDE5 inhibition in the bladder are the urothelium, suburothelial interstitial cells and blood vessels, rather than the bladder nerve fibres.

Reflexes, that involve the spinobulbospinal pathway control both storage and voiding of urine. The periaqueductal gray matter (PAG), a pontine structure is part of the micturition pathway. Alteration in this pathway could lead to micturition disorders and urinary incontinence, such as the overactive bladder symptom complex (OABS). Although different therapeutic options exist for the management of OABS, these are either not effective in all patients. Part of the pathology of OABS is faulty sensory signaling about the filling status of the urinary bladder, which results in aberrant efferent signaling leading to overt detrusor contractions and the sensation of urgency and frequent voiding. In order to identify novel targets for therapy (i.e., structures in the central nervous system) and explore novel treatment modalities such as neuromodulation, we aimed at investigating which areas in the central nervous system are functionally activated upon sensory afferent stimulation of the bladder. Hence, we designed a robust protocol with multiple readout parameters including immunohistological and behavioral parameters during electrical stimulation of the rat urinary bladder. Bladder stimulation induced by electrical stimulation, below the voiding threshold, influences neural activity in: (1) the caudal ventrolateral PAG, close to the aqueduct; (2) the pontine micturition center and locus coeruleus; and (3) the superficial layers of the dorsal horn, sacral parasympathetic nucleus and central canal region of the spinal cord. In stimulated animals, a higher voiding frequency was observed but was not accompanied by increase in anxiety level and locomotor deficits. Taken together, this work establishes a critical role for the vlPAG in the processing of sensory information from the urinary bladder and urges future studies to investigate the potential of neuromodulatory approaches for urological diseases.