In vivo study on the effects of α1-adrenoceptor antagonists on intraurethral pressure in the prostatic urethra and intraluminal pressure in the vas deferens in male dogs

Retrospective evaluation of prazosin and diazepam after thoracolumbar hemilaminectomy in dogs

Management of urinary retention after spinal cord injury in dogs is often needed and can include use of medications to relax the urethral sphincter. This was a retrospective study evaluating two such medications, prazosin and diazepam, and whether dogs treated with these medications had different lengths of hospitalization, urinary continence levels, or development of bacteriuria compared to dogs not receiving these medications after thoracolumbar hemilaminectomy for intervertebral disc herniation (IVDH). Electronic medical records were searched for dogs that underwent CT or MRI followed by a hemilaminectomy between the 3^rd thoracic and 3rd lumbar vertebra for treatment of IVDH. Dogs were grouped based on whether or not they received a medication to aid in urethral sphincter relaxation (either prazosin, diazepam, or both medications). The total length of hospitalization, urinary continence at the time of discharge, and presence of bacteriuria were recorded from the medical file. Medical records from 71 dogs were included in the analysis. There were no significant associations between administration of prazosin and/or diazepam and length of hospitalization or urinary continence scores at the time of discharge from the hospital (P > 0.05).

Cardiovascular/Pulmonary Medications and Male Reproduction

Cardiovascular and respiratory medications are used by men of reproductive age although use of the former is most prevalent in advanced age. Many of these drugs have been associated with sexual dysfunction, including erectile and ejaculatory dysfunction, but for most there is insufficient evidence to link their use with testicular dysfunction, reduced semen quality or infertility. Some exceptions are the irreversible α₁-adrenergic antagonist phenoxybenzamine, which carries a high risk of retrograde ejaculation; the specific α_1A-adrenergic antagonists silodosin and tamsulosin, used primarily to treat BPH/lower urinary tract symptoms, which can cause retrograde ejaculation; and the peripheral β₁-adrenergic antagonist atenolol, used to treat hypertension, which may decrease testosterone/free-testosterone levels. In this chapter, we review the evidence available regarding adverse reactions on male reproduction of adrenergic receptor agonists/antagonists, calcium channel blockers, angiotensin converting enzyme (ACE) inhibitors, diuretics, digoxin, and hydralazine. For some of these medications, there is some evidence for male reproductive effects, along with some solid work in experimental and companion animal species suggesting negative effects. In contrast, and of special note, are calcium channel blockers, which have long been included on lists of medications with the potential to cause male infertility. This turns out to be a good example of a substance with profound effects on sperm function in vitro, but with limited evidence for in vivo effects on semen quality or fertility, even in experimental species. We hope that the evidence provided in this chapter will stimulate additional studies for these important classes of medications.

Mechanisms Underlying Activation of α₁-Adrenergic Receptor-Induced Trafficking of AQP5 in Rat Parotid Acinar Cells under Isotonic or Hypotonic Conditions

Defective cellular trafficking of aquaporin-5 (AQP5) to the apical plasma membrane (APM) in salivary glands is associated with the loss of salivary fluid secretion. To examine mechanisms of α₁-adrenoceptor (AR)-induced trafficking of AQP5, immunoconfocal microscopy and Western blot analysis were used to analyze AQP5 localization in parotid tissues stimulated with phenylephrine under different osmolality. Phenylephrine-induced trafficking of AQP5 to the APM and lateral plasma membrane (LPM) was mediated via the α_1A-AR subtype, but not the α_1B- and α_1D-AR subtypes. Phenylephrine-induced trafficking of AQP5 was inhibited by ODQ and KT5823, inhibitors of nitric oxide (NO)-stimulated guanylcyclase (GC) and protein kinase (PK) G, respectively, indicating the involvement of the NO/ soluble (c) GC/PKG signaling pathway. Under isotonic conditions, phenylephrine-induced trafficking was inhibited by La³⁺, implying the participation of store-operated Ca²⁺ channel. Under hypotonic conditions, phenylephrine-induced trafficking of AQP5 to the APM was higher than that under isotonic conditions. Under non-stimulated conditions, hypotonicity-induced trafficking of AQP5 to the APM was inhibited by ruthenium red and La³⁺, suggesting the involvement of extracellular Ca²⁺ entry. Thus, α_1A-AR activation induced the trafficking of AQP5 to the APM and LPM via the Ca²⁺/ cyclic guanosine monophosphate (cGMP)/PKG signaling pathway, which is associated with store-operated Ca²⁺ entry.

Silodosin in the management of lower urinary tract symptoms as a result of benign prostatic hyperplasia: who are the best candidates

BACKGROUND

As the clinical effects of the available α1-adrenoceptors (ARs) blockers are usually considered comparable for treatment in patients suffering from lower urinary tract symptoms (LUTS) secondary to prostatic enlargement, officially recognised guidelines do not make specific recommendations regarding the choice of which agent should be considered according to the patient's characteristics.

AIM

To analyse data supporting the use of silodosin, a highly selective once-daily dosing α1-ARs blocker, in different daily clinical practice scenarios.

MATERIALS AND METHODS

A structured literature review was performed using data retrieved from articles assessing the role of silodosin in the management of LUTS secondary to benign prostatic hyperplasia (BPH). A literature search of English language publications was performed using MEDLINE(®) and Web of Science from 2000 to 2012 using the terms LUTS; BPH; silodosin; α1-ARs blockers. The papers with the highest level of evidence were identified and represent the basis of the present review.

RESULTS

Available data coming from basic research analyses, randomised trials and prospective studies showed that silodosin is efficacious for the initial management of patients with LUTS. Clinical developmental safety data from patients receiving silodosin with concomitant antihypertensive therapy do not indicate an increase in risk of orthostatic hypotension. In this context, a recent study demonstrated that silodosin can be safely administered to patients who are consensually assuming phosphodiesterase type 5 inhibitors. A recent randomised crossover study comparing the efficacy of silodosin and tamsulosin in patients with LUTS showed that further significant improvement was observed after switching to silodosin treatment, while worsening or little improvement was observed after switching to tamsulosin treatment. Preliminary results seem to demonstrate a potential role of silodosin in the treatment of chronic prostatitis/chronic pelvic pain syndrome and to facilitate ureteral stone passage, as well.

DISCUSSION

When considering the above cited pharmacological and clinical characteristics of the drug, silodosin can be considered in the following clinical scenario: patients suffering from moderate-severe nocturia, patients with low normal blood pressure levels and patients concomitantly treated with antihypertensive medications, patients concomitantly treated with phosphodiesterase type 5 inhibitors, patients not satisfied (for efficacy or tolerability) with previous treatment with other α1-ARs blockers.

CONCLUSION

Silodosin is efficacious for the initial management of patients with LUTS. Silodosin has a good cardiovascular safety profile and can be considered an option in patients with cardiovascular co-morbidities. It seems to be especially beneficial in patients with nocturia alone or presenting with the symptomatic trial nocturia-frequency-incomplete emptying. Patients on phosphodiesterase type 5 inhibitors treatment can be safely managed with silodosin.

Non-inferiority of silodosin to tamsulosin in treating patients with lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH)

What's known on the subject? and What does the study add? Silodosin administered by 4 mg twice daily is as effective as tamsulosin 0.2 mg daily in treating patients with LUTS associated with BPH. Relative to tamsulosin, silodosin has less cardiovascular side effects as judged by the minimal changes of blood pressure and pulse rats after treatment.

OBJECTIVE

• To test the hypothesis that the efficacy of silodosin would not be inferior to tamsulosin in treating patients with lower urinary tract symptoms associated with benign prostate hyperplasia (BPH).

PATIENTS AND METHODS

• At nine medical centres, 209 patients with an International Prostate Symptom Score (IPSS) of ≥13 were randomized to silodosin (4 mg twice daily) or tamsulosin (0.2 mg once daily) for 12 weeks. • The primary efficacy measure was the mean change from baseline to endpoint in IPSS. • The non-inferiority margin of the IPSS change was set at 1.0. • Secondary efficacy measures included change in maximal urinary flow rate (Q(max)) and health-related quality of life (HRQL) score.

RESULTS

• Of the 170 (81.3%) patients who completed the study, 86.2% in the silodosin group vs 81.9% in the tamsulosin group achieved a ≥25% decrease in IPSS (P= 0.53). • The mean difference (silodosin minus tamsulosin) in IPSS change from baseline was -0.60 (95% confidence interval -2.15, 0.95), inferring the non-inferiority of silodosin to tamsulosin. • The mean changes in the Q(max) and HRQL score from baseline were comparable between the groups (both, P > 0.05). Although patients receiving silodosin had a significantly higher incidence of abnormal ejaculation (9.7% vs tamsulosin 1.0%, P= 0.009), only 1.9% discontinued treatment. • Tamsulosin treatment resulted in a significant reduction in mean systolic blood pressure (-4.2 mmHg, within-group P= 0.004) relative to the negligible change of silodosin (-0.1 mmHg, within-group P= 0.96)

CONCLUSION

• The trial shows the non-inferiority of silodosin 4 mg twice daily to tamsulosin 0.2 mg once daily in patients with symptoms of BPH.

Animal models for benign prostatic hyperplasia

Although the etiology of benign prostatic hyperplasia (BPH) is unknown, various animal models have been used for several decades to identify potential therapeutic approaches. These models can be divided into those measuring smooth muscle tone and those measuring cellular proliferation. Animal models have played an important role in the development of the two drug classes currently approved for the treatment of BPH: the α-adrenoceptor antagonists and the steroid 5-α-reductase inhibitors. However, models measuring prostatic tone have not been particularly useful in the identification of new α-adrenoceptor antagonists having advantages over currently available drugs, and it is not certain that reduction of prostatic smooth muscle tone is responsible for the relief of BPH symptoms. A further limitation with BPH models is that prostatic hyperplasia similar to the human condition does not occur spontaneously or cannot be induced in any suitable animal species. The identification of a more useful BPH model is focused on cellular mechanisms of prostatic growth, looking similarities between humans and experimental animals.

Silodosin: an orally active selective α1-adrenoceptor antagonist for benign prostatic hyperplasia

α1-adrenoceptor antagonists play a central role in the treatment of uncomplicated symptomatic benign prostatic hyperplasia, frequently in combination with the 5-α-reductase inhibitors such as finasteride and dutasteride. Clinically useful examples include alfuzosin, doxazosin, tamsulosin and terazosin. These can be subdivided into nonselective (doxazosin and terazosin) and uroselective (alfuzosin and tamsulosin) agents. In general, these agents appear to be equieffective. However, they can be distinguished on the basis of their adverse event profiles. Such adverse events include those due to their vasodilatory effects (dizziness, orthostatic hypotension and rhinitis), genitourinary effects (ejaculatory dysfunction) and nonspecific effects (e.g., asthenia, malaise and gastrointestinal upset). A new α1A-adrenoceptor antagonist, silodosin, has recently been approved. In most ways, it is similar to tamsulosin in its pharmacodynamic effects in vitro and in vivo (in both animals and humans). Limited clinical trial data have shown silodosin to significantly improve lower urinary tract symptoms associated with benign prostatic hyperplasia and quality of life, with effects sustainable for at least 1 year. Its adverse-event profile reflects that seen with other uroselective α-adrenoceptor antagonists with the exception of a relatively high-incidence rate of ejaculatory dysfunction (22 vs 2% with tamsulosin and 28 vs 1% with placebo). This article reviews the preclinical and clinical data concerning silodosin and introduces the reader to this new drug for the treatment of benign prostatic hyperplasia.