Nitrergic relaxations and phenylephrine contractions are not compromised in isolated urethra in a rat model of diabetes

Therapeutic effects of silodosin and urapidil on underactive bladder associated with diabetic cystopathy

OBJECTIVES

Pharmacological treatment options for underactive bladder (UAB) syndrome are limited. Urapidil is the only alpha₁ -adrenoceptor (AR) antagonist that can be used for urinary disorders in women in some countries. However, no studies have directly verified the effects of alpha₁ -AR antagonists on the female urethra and UAB-like dysfunctions. We investigated the effects of silodosin (alpha_1A -AR antagonist) and urapidil (nonselective alpha₁ -AR antagonist) on the voiding function in female rats with diabetes mellitus (DM).

METHODS

Changes in intraurethral pressure (IUP) induced by midodrine (alpha₁ -AR agonist) and mean blood pressure (MBP) were continuously measured in normal female rats to verify the pharmacological profiles of the drugs. To establish a DM model, rats were administered streptozotocin (STZ; 50 mg/kg, intravenous). Eight weeks after STZ administration, drugs were subcutaneously delivered through an osmotic pump. Four weeks after drug administration, emptied bladder blood flow (BBF), intravesical pressure, and the micturition volume were measured.

RESULTS

Both silodosin and urapidil inhibited the midodrine-induced increase in IUP and decreased MBP in a dose-dependent manner. Silodosin had a more substantial effect on the lower urinary tract than on MBP. Twelve weeks after STZ administration, DM rats exhibited UAB-like dysfunction (increased bladder capacity/bladder weight and residual volume and decreased bladder voided efficiency) and decreased BBF. Both drug treatments controlled this dysfunction.

CONCLUSIONS

Alpha₁ -AR antagonists induced dose-dependent urethral relaxation in female rats. These drugs ameliorated UAB-like dysfunction in STZ-induced DM rats. In addition, alpha_1A -AR antagonists such as silodosin, which have limited effects on blood pressure, appear to be useful for treating UAB.

Urethral dysfunction and alterations of nitric oxide mechanisms in streptozotocin-induced diabetic rats with or without low-dose insulin treatment

AIMS

To establish an animal model of diabetes mellitus (DM) with moderately elevated blood glucose levels, and to examine the nitric oxide (NO) mechanism controlling urethral function in streptozotocin (STZ)-induced DM rats.

MAIN METHODS

Female Sprague-Dawley rats were used. DM was induced by intraperitoneal injection of STZ (65 mg/kg) and some of them received subcutaneous implantation of a low-dose insulin pellet. Voiding behavior was evaluated in metabolic cages. Isovolumetric cystometry and urethral perfusion pressure (UPP) were then evaluated under urethane anesthesia, during which L-arginine (100 mg/kg) and N-nitro-L-arginine methyl ester hydrochloride (L-NAME) (50 mg/kg) were administered intravenously. In vitro urethral activity was also tested by organ bath muscle strip studies.

KEY FINDINGS

UPP changes and high-frequency oscillation (HFO) were significantly (P < 0.05) smaller in 8-weeks DM rats vs. normal control (NC) rats or insulin-treated DM rats, which showed reductions in urine overproduction and voided volume per micturition vs. untreated DM rats. UPP nadir was decreased by L-arginine in NC and insulin-treated DM groups, and decreased by L-NAME in all groups. Five of 6 untreated DM rats showed a detrusor-sphincter dyssynergia pattern after L-NAME. In in vitro studies, the relative ratio of L-NAME-induced reductions of urethral relaxation against pre-drug urethral relaxation was significantly smaller in DM vs. NC rats (P < 0.05).

SIGNIFICANCE

Low-dose insulin-treated DM rats would be a useful model for studying natural progression of DM-induced lower urinary tract dysfunction. The impaired NO-mediated urethral relaxation mechanisms play an important role in DM-induced urethral dysfunction, which could contribute to DM-induced inefficient voiding.

Time-Dependent Changes of Urethral Function in Diabetes Mellitus: A Review

This article reviewed the current knowledge on time-course manifestation of diabetic urethral dysfunction (DUD), and explored an early intervention target to prevent the contribution of DUD to the progression of diabetes-induced impairment of the lower urinary tract (LUT). In the literature search through PubMed, key words used included “diabetes mellitus,” “diabetic urethral dysfunction,” and “diabetic urethropathy.” Polyuria and hyperglycemia induced by diabetes mellitus (DM) can cause the time-dependent changes in functional and morphological manifestations of DUD. In the early stage, it promotes urethral dysfunction characterized by increased urethral pressure during micturition. However, the detrusor muscle of the bladder tries to compensate for inducing complete voiding by increasing the duration and amplitude of bladder contractions. As the disease progresses, it can induce an impairment of coordinated micturition due to dyssynergic activity of external urethra sphincter, leading to detrusor-sphincter dyssynergia. The impairment of relaxation mechanisms of urethral smooth muscles (USMs) may additionally be attributable to decreased responsiveness to nitric oxide, as well as increased USM responsiveness to α₁-adrenergic receptor stimulation. In the late stage, diabetic neuropathy may play an important role in inducing LUT dysfunction, showing that the decompensation of the bladder and urethra, which can cause the decrease of voiding efficiency and the reduced thickness of the urothelium and the atrophy of striated muscle bundles, possibly leading to the vicious cycle of the LUT dysfunction. Further studies to increase our understandings of the functional and molecular mechanisms of DUD are warranted to explore potential targets for therapeutic intervention of DM-induced LUT dysfunction.

Serotonergic paraneurones in the female mouse urethral epithelium and their potential role in peripheral sensory information processing

AIM

The mechanisms underlying detection and transmission of sensory signals arising from visceral organs, such as the urethra, are poorly understood. Recently, specialized ACh-expressing cells embedded in the urethral epithelium have been proposed as chemosensory sentinels for detection of bacterial infection. Here, we examined the morphology and potential role in sensory signalling of a different class of specialized cells that express serotonin (5-HT), termed paraneurones.

METHODS

Urethrae, dorsal root ganglia neurones and spinal cords were isolated from adult female mice and used for immunohistochemistry and calcium imaging. Visceromotor reflexes (VMRs) were recorded in vivo.

RESULTS

We identified two morphologically distinct groups of 5-HT+ cells with distinct regional locations: bipolar-like cells predominant in the mid-urethra and multipolar-like cells predominant in the proximal and distal urethra. Sensory nerve fibres positive for calcitonin gene-related peptide, substance P, and TRPV1 were found in close proximity to 5-HT+ paraneurones. In vitro 5-HT (1 μm) stimulation of urethral primary afferent neurones, mimicking 5-HT release from paraneurones, elicited changes in the intracellular calcium concentration ([Ca2+ ]i ) mediated by 5-HT2 and 5-HT3 receptors. Approximately 50% of 5-HT responding cells also responded to capsaicin with changes in the [Ca2+ ]i . In vivo intra-urethral 5-HT application increased VMRs induced by urethral distention and activated pERK in lumbosacral spinal cord neurones.

CONCLUSION

These morphological and functional findings provide insights into a putative paraneurone-neural network within the urethra that utilizes 5-HT signalling, presumably from paraneurones, to modulate primary sensory pathways carrying nociceptive and non-nociceptive (mechano-sensitive) information to the central nervous system.

Path of translational discovery of urological complications of obesity and diabetes

Diabetes mellitus (DM) is a prevalent chronic disease. Type 1 DM (T1DM) is a metabolic disorder that is characterized by hyperglycemia in the context of absolute lack of insulin, whereas type 2 DM (T2DM) is due to insulin resistance-related relative insulin deficiency. In comparison with T1DM, T2DM is more complex. The natural history of T2DM in most patients typically involves a course of obesity to impaired glucose tolerance, to insulin resistance, to hyperinsulinemia, to hyperglycemia, and finally to insulin deficiency. Obesity is a risk factor of T2DM. Diabetes causes some serious microvascular and macrovascular complications, such as retinopathy, nephropathy, neuropathy, angiopathy and stroke. Urological complications of obesity and diabetes (UCOD) affect quality of life, but are not well investigated. The urological complications in T1DM and T2DM are different. In addition, obesity itself affects the lower urinary tract. The aim of this perspective is to review the available data, combined with the experience of our research teams, who have spent a good part of last decade on studies of association between DM and lower urinary tract symptoms (LUTS) with the aim of bringing more focus to the future scientific exploration of UCOD. We focus on the most commonly seen urological complications, urinary incontinence, bladder dysfunction, and LUTS, in obesity and diabetes. Knowledge of these associations will lead to a better understanding of the pathophysiology underlying UCOD and hopefully assist urologists in the clinical management of obese or diabetic patients with LUTS.

Biphasic Effect of Diabetes on Neuronal Nitric Oxide Release in Rat Mesenteric Arteries

INTRODUCTION

We analysed possible time-dependent changes in nitrergic perivascular innervation function from diabetic rats and mechanisms implicated.

MATERIALS AND METHODS

In endothelium-denuded mesenteric arteries from control and four- (4W) and eight-week (8W) streptozotocin-induced diabetic rats the vasoconstriction to EFS (electrical field stimulation) was analysed before and after preincubation with L-NAME. Neuronal NO release was analysed in the absence and presence of L-arginine, tetrahydrobiopterine (BH4) and L-arginine plus BH4. Superoxide anion (O2-), peroxynitrite (ONOO-) and superoxide dismutase (SOD) activity were measured. Expressions of Cu-Zn SOD, nNOS, p-nNOS Ser1417, p-nNOS Ser847, and Arginase (Arg) I and II were analysed.

RESULTS

EFS response was enhanced at 4W, and to a lesser extent at 8W. L-NAME increased EFS response in control rats and at 8W, but not at 4W. NO release was decreased at 4W and restored at 8W. L-arginine or BH4 increased NO release at 4W, but not 8W. SOD activity and O2- generation were increased at both 4W and 8W. ONOO- decreased at 4W while increased at 8W. Cu-Zn SOD, nNOS and p-NOS Ser1417 expressions remained unmodified at 4W and 8W, whereas p-nNOS Ser847 was increased at 4W. ArgI was overexpressed at 4W, remaining unmodified at 8W. ArgII expression was similar in all groups.

CONCLUSIONS

Our results show a time-dependent effect of diabetes on neuronal NO release. At 4W, diabetes induced increased O2- generation, nNOS uncoupling and overexpression of ArgI and p-nNOS Ser847, resulting in decreased NO release. At 8W, NO release was restored, involving normalisation of ArgI and p-nNOS Ser847 expressions.

Ion channels of the mammalian urethra

The mammalian urethra is a muscular tube responsible for ensuring that urine remains in the urinary bladder until urination. In order to prevent involuntary urine leakage, the urethral musculature must be capable of constricting the urethral lumen to an extent that exceeds bladder intravesicular pressure during the urine-filling phase. The main challenge in anti-incontinence treatments involves selectively-controlling the excitability of the smooth muscles in the lower urinary tract. Almost all strategies to battle urinary incontinence involve targeting the bladder and as a result, this tissue has been the focus for the majority of research and development efforts. There is now increasing recognition of the value of targeting the urethral musculature in the treatment and management of urinary incontinence. Newly-identified and characterized ion channels and pathways in the smooth muscle of the urethra provides a range of potential therapeutic targets for the treatment of urinary incontinence. This review provides a summary of the current state of knowledge of the ion channels discovered in urethral smooth muscle cells that regulate their excitability.