Local renin–angiotensin systems in the genitourinary tract

Insights into the associative role of hypertension and angiotensin II receptor in lower urinary tract dysfunction

In men, the lower urinary tract comprises the urinary bladder, urethra, and prostate, and its primary functions include urine storage and voiding. Hypertension is a condition that causes multi-organ damage and an age-dependent condition. Hypertension and the renin-angiotensin system activation are associated with the development of lower urinary tract dysfunction. Hypertensive animal models show bladder dysfunction, urethral dysfunction, and prostatic hyperplasia. In the renin-angiotensin system, angiotensin II and the angiotensin II type 1 receptor, which are expressed in the lower urinary tract, have been implicated in the pathogenesis of lower urinary tract dysfunction. Moreover, among the several antihypertensives, renin-angiotensin system inhibitors have proven effective in human and animal models of lower urinary tract dysfunction. This review aimed to elucidate the hitherto known mechanisms underlying the development of lower urinary tract dysfunction in relation to hypertension and the angiotensin II/angiotensin II type 1 receptor axis and the effect of renin-angiotensin system inhibitors on lower urinary tract dysfunction. Possible mechanisms through which hypertension or activation of Ang II/AT1 receptor axis causes LUTD such as bladder dysfunction, urethral dysfunction, and prostatic hyperplasia. LUT: lower urinary tract, LUTD: lower urinary tract dysfunction, AT1: angiotensin II type 1, ACE: angiotensin-converting enzyme.

Micturition dysfunction in four-month old ovariectomized rats: Effects of testosterone replacement

AIMS

Androgen deficiency has been implicated in urological complications of postmenopausal women. This study examined the effects of testosterone replacements on the lower urinary tract dysfunction in 4-month old ovariectomized (OVX) rats.

MAIN METHODS

Sprague-Dawley female rats were OVX bilaterally. Three months later, rats received single intramuscular injections of testosterone undecanoate. Cystometric study, and bladder and urethra smooth muscle reactivities were evaluated.

KEY FINDINGS

Ovariectomy reduced by 65% (p<0.05) the serum testosterone levels. Testosterone replacement at 5mg/kg restored serum hormone levels to baseline, whereas 10mg/kg produced 14-fold higher testosterone levels. OVX rats exhibited significant increases of body weight, perigonadal fat and blood pressure, and reduced uterus weight, but none of these parameters were changed by testosterone replacements. OVX rats exhibited micturition dysfunction characterized by increases of basal pressure, threshold pressure, voiding frequency and post-voiding pressure. In addition, the bladder contractions induced by electrical-field stimulation (EFS) and carbachol were significantly reduced, whereas angiotensin II-induced urethral contractions were significantly increased in OVX rats. Testosterone replacement at 10mg/kg (but not at 5mg/kg) dose fully normalized the in vivo micturition dysfunction, as well as the in vitro bladder and urethral alterations. Testosterone (10mg/kg) also significantly potentiated the bladder relaxations induced by the β₃-adrenoceptor agonist mirabegron. The protective effects of testosterone were not modified by concomitant treatment with the aromatase inhibitor letrozole (2.5mg/kg, 4weeks).

SIGNIFICANCE

The improvement of micturition dysfunction by testosterone replacement suggests that androgen therapy might be of therapeutic benefit for urological complications associated with post-menopause.

Arterial hypertension related to the injection of onabotulinumtoxinA in the detrusor

OBJECTIVE AND IMPORTANCE

We want to report on a first case reported of a 50-year-old female with repetitive and clinical significant hypertension after each injection of onabotulinumtoxinA. This is a retrospective chart review and prospective evaluation of the natriuresis and blood pressure at baseline and after injection therapy. The aim was to explore the mechanism of action of this apparent onabotulinumtoxinA related hypertension.

CASE PRESENTATION

Retrospectively hypertension appeared after 7 days and vanished after 4-5 months following injection of 300 units of onabotulinumtoxinA in the detrusor, bladder symptoms disappeared after 2 weeks and reoccurred after 5 months. Urological, nephrological, cardiological and endocrinological evaluations were normal.

INTERVENTION

In the prospective evaluation a 3-day bladder diary at baseline revealed a bladder capacity of 131 ± 57 ml and at 1 month when full effect was experienced 173 ± 50 ml. At 1 month there were no leakages with six episodes of intermittent catheterization per day. The 24-hour blood pressure registration demonstrated the onset of hypertension at day 7 together with a reversal of the urinary sodium/creatinine ratios on the renal function profile.

CONCLUSION

The increasing natriuresis coinciding with the hypertension is a normal compensatory mechanism suggesting that the hypertension has a central cause rather than it is caused by haematogenous spreading.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

Pharmacological profile of β3-adrenoceptor agonists in clinical development for the treatment of overactive bladder syndrome

β(3)-Adrenoceptor agonists are an emerging drug class for the treatment of the overactive bladder syndrome, and clinical proof-of-concept data have been obtained for three representatives of this class, mirabegron, ritobegron, and solabegron. We review here the pharmacological profile of these three drugs and discuss the potential clinical relevance of differences between them. In the absence of direct comparative studies, it appears that all three are strong agonists selective for β(3)- vs. β(1)- and β(2)-adrenoceptors in studies with cloned receptor subtypes. The potency of these agonists may be species-dependent, with all three having high potency in the human detrusor. All three agonists were effective in one or more animal models of bladder dysfunction, which typically involved reductions of micturition frequency. Agonist doses effective for bladder function lowered blood pressure in some cases, but the relevance of this for clinical use is difficult to determine due to species differences in the importance of cardiovascular β(3)-adrenoceptors. While limited effects on other organ systems are expected for β(3)-adrenoceptor agonists, this requires further investigation.