The pharmacology of α1-adrenoceptor subtypes

This review examines the functions of α₁-adrenoceptor subtypes, particularly in terms of contraction of smooth muscle. There are 3 subtypes of α₁-adrenoceptor, α_1A- α_1B- and α_1D-adrenoceptors. Evidence is presented that the postulated α_1L-adrenoceptor is simply the native α_1A-adrenoceptor at which prazosin has low potency. In most isolated tissue studies, smooth muscle contractions to exogenous agonists are mediated particularly by α_1A-, with a lesser role for α_1D-adrenoceptors, but α_1B-adrenoceptors are clearly involved in contractions of some tissues, for example, the spleen. However, nerve-evoked responses are the most crucial physiologically, so that these studies of exogenous agonists may overestimate the importance of α_1A-adrenoceptors. The major α₁-adrenoceptors involved in blood pressure control by sympathetic nerves are the α_1D- and the α_1A-adrenoceptors, mediating peripheral vasoconstrictor actions. As noradrenaline has high potency at α_1D-adrenceptors, these receptors mediate the fastest response and seem to be targets for neurally released noradrenaline especially to low frequency stimulation, with α_1A-adrenoceptors being more important at high frequencies of stimulation. This is true in rodent vas deferens and may be true in vasopressor nerves controlling peripheral resistance and tissue blood flow. The α_lA-adrenoceptor may act mainly through Ca²⁺ entry through L-type channels, whereas the α_1D-adrenoceptor may act mainly through T-type channels and exhaustable Ca²⁺ stores. α₁-Adrenoceptors may also act through non-G-protein linked second messenger systems. In many tissues, multiple subtypes of α-adrenoceptor are present, and this may be regarded as the norm rather than exception, although one receptor subtype is usually predominant.

Silodosin: An Update on Efficacy, Safety and Clinical Indications in Urology

INTRODUCTION

Silodosin determines smooth muscle relaxation in bladder and prostate tissues, increases bladder blood flow in conditions of chronic bladder ischemia and regulates the activity of transcriptional factors responsible for stromal growth and prostate hyperplasia. Phase III trials have already demonstrated the efficacy and safety of silodosin in the treatment of patients bothered by lower urinary tract symptoms (LUTS) secondary to benign prostatic hyperplasia (BPH).

OBJECTIVE

We aimed to describe the rationality for the use of silodosin and to summarize the current literature on the use of Silodosin for the treatment of LUTS.

METHODS

PubMed and Web of Science were queried with the terms: 'silodosin' in combination (AND) with the terms 'lower urinary tract symptoms', 'LUTS', 'pathophysiology', 'symptoms' OR 'therapy'. Studies published in the last 10 years (2007-2017) in adults and core clinical journals in English were included.

RESULTS

Silodosin 8 mg once-daily was superior to placebo in improving IPSS total score, voiding subscore, storage subscore and QoL score, and at least as effective as tamsulosin 0.4 mg once-daily in all the efficacy analyses. In addition, studies assessing the effect on urodynamic parameters showed that silodosin determined a higher improvement in the bladder outlet obstruction index compared to other alpha1 adrenergic receptor antagonists. Concerning the safety profile, long-term data (after 9 months of treatment) confirmed the limited effect of silodosin on the cardiovascular and gastrointestinal systems. Although ejaculatory disorders represented the main complaint of patients taking silodosin, the discontinuation rate due to this condition remained low even in a long-term follow-up study (7.5%). Encouraging findings showed that silodosin may be administered as a medical expulsive therapy for promoting spontaneous stone passage of distal ureteral stones < 10 mm, to relieve LUTS in patients who underwent prostate cancer brachytherapy and to increase the likelihood of successful trials without a catheter in patients experiencing acute urinary retention.

CONCLUSION

Silodosin is one of the drugs approved for the treatment of BPH, being highly effective in improving not only LUTS but also urodynamic parameter impairments secondary to BPH. Moreover, it has shown efficacy as medical expulsive therapy for distal ureteral stones in previous prospective randomized trials.

FUNDING

Sponsorship for this study and article processing charges were funded by Recordati.

The modulation of ureteral smooth muscle contractile responses by α1- and α2-adrenoceptor activation

PURPOSE

This study was performed to investigate the influence of α-adrenoceptor subtypes upon ureteral smooth muscle contractile responses.

METHODS

Rat ureters were challenged in vitro with noradrenaline (NA), the α₁-adrenoceptor agonist phenylephrine (PE), and the α₂-adrenoceptor agonist clonidine (CLON). The influences of the agonists on the magnitude and frequency of acetylcholine (ACh)-stimulated phasic contractile responses were recorded.

RESULTS

The magnitude of the phasic contractile responses effected by ACh was not significantly influenced by the adrenoceptor agonists, but the frequency of the response was significantly enhanced by all three agonists (p < 0.05). Idazoxan and prazosin abolished the rise in frequency effected by CLON and PE, respectively, whereas both antagonists in combination were required to abolish the increase in frequency effected by NA.

CONCLUSIONS

It has been demonstrated that α₁- and α₂-adrenoceptors modulate the contractile function of rat ureteral smooth muscle by increasing the frequency, but not the magnitude, of phasic contractile responses. The enhancement of contractile function by NA is mediated by mechanisms dependent upon both α₁- and α₂-adrenoceptors.

The effect of alfuzosin on renal resistive index, urinary electrolytes and β2 microglobulin levels and TGF β-1 levels of kidney tissue in rats with unilateral ureteropelvic junction obstruction

BACKGROUND

In this study, it was aimed to determine the effects of alfuzosin on experimentally generated unilateral partial ureteropelvic junction obstruction (UPO) in rats.

MATERIALS AND METHODS

Thirty Long-Evans rats were randomly allocated into five groups. In control group (C), nothing was performed; in group Sham (S) only laparotomy was done; in Alfuzosin group (A) only alfuzosin was administered for two weeks (10 mg/kg/day p.o.) without any surgery; in UPO group, unilateral UP junction obstruction was produced; and in the Group UPT (ureteropelvic obstruction + treatment), alfuzosin was administered for two weeks (10 mg/kg/day p.o.) in addition to UPO production. Renal pelvic anteroposterior diameters were determined with ultrasonography (USG) and renal arterial resistivity indexes by color Doppler USG. Urine was collected both at the beginning and at the end of the experiment for 24 h in all the groups and at the end of the experiment, blood samples were obtained. Blood and urine electrolytes and TGF-β1, urine density, urine β2 microglobulin levels were determined. Renal tissue samples harvested from all of the rats were histopathologically evaluated. Results were determined using one-way ANOVA t-test; p < 0.05 was accepted as significant.

RESULTS

Urine density in the UPT group was lower with respect to UPO group and blood electrolytes were preserved as close to normal (p < 0.05). In the UPT group, urine TGF-β1 and blood TGF-β1, blood β2 microglobulin levels and histopathologic damage scores were lower compared to the UPO group (p < 0.05).

CONCLUSION

It is shown in this experimental unilateral partial UPO model that alfuzosin treatment prevents obstructive renal damage.

Alpha adrenergic receptors in renal pelvis and calyces: can rat models be used?

We aimed, in this study, to determine the distribution of α-1 AR subtypes in rat and human pelvis and calyces, and to evaluate, by comparing these two species, the possibility of rats to be used as models for humans. Twenty patients with renal carcinoma were included into the study. The patients underwent radical nephrectomy for renal cell carcinoma (RCC). After nephrectomy, specimens were evaluated and excisional biopsies from healthy pelvis and calyces tissues were performed. When pathology confirmed the non-invasion of RCC, specimen was included into the study. A total of 7 adult Wistar Albino (250-300 g) female rats were used in this study. Specimens included renal pelvis and calyces. All specimens were evaluated under light microscope histopathologically. The concentrations of the receptor densities did not differ between the two groups. With the demonstration of the α receptors in rat kidneys and calyces, many receptor-based studies concerning both humans and rats can take place. Novel medication targeting these subtypes -in this matter α1A and α1D for renal pelvis and calyces- may be helpful for expulsive therapy and/or pain relief. With the demonstration of similar receptor densities between human and rat tissues, rat model may be useful for α-receptor trials for renal pelvis and calyces.

The presence and distribution of alpha adrenergic receptors in human renal pelvis and calyces

In this study, we aimed to demonstrate the presence of Alpha (α) 1 receptors and subtypes in human pelvis and calyces, because an agent to facilitate kidney stone movement and help decrease pain may be an α 1 adrenergic blocker, as used in ureteral stones. Twenty patients who applied to our clinic for renal cell carcinoma were enrolled to the study. All patients underwent radical nephrectomy. After the specimens were removed, excisional biopsies were performed on healthy pelvises and calyces. Mean α-receptor stain rates in renal pelvis were 2.65 ± 0.74, 1.35 ± 0.81 and 2.9 ± 0.30 for α 1A, 1B and 1D, respectively. For calyces, the rates are 2.40 ± 0.82, 1.50 ± 0.76 and 2.75 ± 0.44 for α 1A, 1B and 1D, respectively (Fig. 1). When the staining patterns were compared, α 1A and 1D were expressed more in both pelvis and calyces than α 1B (p < 0.05). After the demonstration of α-adrenergic receptors in pelvis and calyces of human kidney, it may be helpful in coming up with new alternative treatments for patients suffering from kidney stones.

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.

Efficacy of alfuzosin after shock wave lithotripsy for the treatment of ureteral calculi

PURPOSE

We evaluated the efficacy of alfuzosin for the treatment of ureteral calculi less than 10 mm in diameter after extracorporeal shock wave lithotripsy (ESWL).

MATERIALS AND METHODS

A randomized, single-blind clinical trial was performed prospectively by one physician between June 2010 and August 2011. A total of 84 patients with ureteral calculi 5 to 10 mm in diameter were divided into two groups. Alfuzosin 10 mg (once daily) and loxoprofen sodium 68.1 mg (as needed) were prescribed to group 1 (n=41), and loxoprofen sodium 68.1 mg (as needed) only was prescribed to group 2 (n=44). The drug administration began immediately after ESWL and continued until stone expulsion was confirmed up to a maximum of 42 days after the procedure.

RESULTS

Thirty-nine of 41 (95.1%) patients in group 1 and 40 of 43 (93.0%) patients in group 2 ultimately passed stones (p=0.96). The number of ESWL sessions was 1.34±0.65 and 1.41±0.85 in groups 1 and 2, respectively (p=0.33). The patients who required analgesics after ESWL were 8 (19.5%) in group 1 and 13 (30.2%) in group 2 (p=0.31). Visual analogue scale pain severity scores were 5.33±1.22 and 6.43±1.36 in groups 1 and 2, respectively (p=0.056). The time to stone expulsion in groups 1 and 2 was 9.5±4.8 days and 14.7±9.8 days, respectively (p=0.005). No significant adverse effects occurred.

CONCLUSIONS

The use of alfuzosin in combination with ESWL seems to facilitate stone passage and to reduce the time of stone expulsion but does not affect the stone-free rate.