Blocking of central angiotensin II type 1 receptors inhibits micturition reflex in rats

Shimizu S1, Shimizu T1, Nagao Y1, Kataoka T1, Kamada S1, Higashi Y1, Aratake T1, Zou S1, Hamada T1, Yamamoto M1, Saito M1

Research Type

Basic Science / Translational

Abstract Category

Pharmacology

Abstract 655
E-Poster 3
Scientific Open Discussion ePoster Session 31
Friday 6th September 2019
13:45 - 13:50 (ePoster Station 10)
Exhibition Hall
Basic Science Pathophysiology Physiology Animal Study
1.Department of Pharmacology, Kochi Medical School, Kochi University, Nankoku, Japan
Presenter
T

Takahiro Shimizu

Links

Abstract

Hypothesis / aims of study
Psychological stress leads to the exacerbation of lower urinary tract symptoms including the overactive bladder and bladder pain syndrome. Stress stimulates the release of angiotensin II (Ang II) and also increases the expression of Ang II type 1 (AT1) receptors in the brain [1]. Our previous reports showed that centrally administered Ang II facilitates micturition reflex via the central AT1 receptors without affecting  maximum voiding pressure (MVP) [2]. However, the precise mechanism is not well clarified. In this study, we investigated the possible mechanism how central Ang II facilitates micturition reflex focusing on the AT1 receptor downstream factor, corticotropin-releasing factor (CRF). According to previous study [2], we also speculated that central AT1 receptors might be therapeutic target against the frequent urination. We investigated whether peripherally administered centrally acting AT1 receptor antagonist, telmisartan inhibits the central Ang II induced facilitation of the micturition reflex.
Study design, materials and methods
Male Wistar rats (330-400 g) were anesthetized with urethane (1.0 g/kg, ip), then catheterized into the bladder dome in order to perform continuous cystometry (12 mL/h saline infusion). Three hours after the surgery, Ang II or each drug was centrally administered. 
Study 1: Vehicle 1 [3 µL of sterile N,N-dimethylmethanamide (DMF)] or CRF type 1 (CRF1) receptor antagonist (CP154526: 3 or 10 nmol/rat) was icv administered 30 min before icv Ang II (30 pmol/rat) or vehicle 2 (3 µL of sterile PBS) administration in the rats.
Study 2: Vehicle 3 (5 µL of sterile DMF) or CRF type 2 (CRF2) receptor antagonist (K41498: 10 nmol/rat) was icv administered 30 min before icv Ang II (30 pmol/rat) administration.
Study 3: CP154526 (10 nmol/rat) was icv administered in rats.
Study 4: Some male Wistar rats were treated with vehicle 4 (0.5% methylcellulose), telmisartan (1 or 10 mg/kg, po) or no centrally acting AT1 receptor antagonist valsartan (10 mg/kg, po) once daily for 8 days. After the treatment, blood pressure was measured by tail cuff method, and then Ang II was icv administered in these rats under the urethane anesthesia during the continuous cytometry. 
The intercontraction interval (ICI) was evaluated 20 min before and after the central Ang II administration (0 to 60 min) (n = 5).
Results
Study 1 and 2: Under the vehicle 1 pre-treatment, centrally administered Ang II significantly shortened ICI compared to the vehicle 2 administration. Central pre-treatment with high dose of CP154526 (10 nmol/rat) but not K41498 significantly inhibited central Ang II-induced shortening of ICI compared to each vehicle pretreatment (Figure 1). 
Study 3: Central CP154526 (10 nmol/rat) administration alone had no effect on ICI compared to that at the pre-administration phase (data not shown).
Study 4: Peripherally administered telmisartan or valsartan did not affect the mean blood pressure in the rats. On the other hands, peripherally administered high dose of telmisartan (10 mg/kg) but not valsartan inhibited the central Ang II-induced shortening of ICI compared to the vehicle 4 treatment (Figure 2).
Interpretation of results
CRF and the two subtypes of receptors, CRF1 and CRF2 are expressed in various regions of brain such as the paraventricular nucleus of the hypothalamus (PVN) and the locus coeruleus [1]. Current study showed that centrally administered CRF1 receptor antagonist CP154526 but not CRF2 receptor antagonist K41498 inhibited the central Ang II-induced shortening of ICI. The current data suggested that CRF1 but not CRF2 receptors are involved in the central Ang II-induced facilitation of the micturition reflex. Moreover, centrally administered CP154526 by itself had no effect on ICI, showing that endogenous CRF in the brain might not affect micturition reflex in normal conditions in the rat. A previous study demonstrated that stimulation of AT1 receptors of the PVN region increases the release of CRF [1]. These data suggested that central Ang II facilitates micturition reflex via AT1 and CRF1 receptors-mediated pathway. Telmisartan was reported to be able to pass through the blood brain barrier and were speculated to block AT1 receptors in the brain [3]. A clinical study showed that telmisartan has beneficial effects on cognitive and regional cerebral blood flow in elderly hypertensive patients with Alzheimer’s disease [3]. These data suggest that AT1 receptor antagonists, which penetrate the blood–brain barrier, might inhibit the facilitation of micturition reflex via blocking of AT1 receptors in the brain. Current data showed that peripherally administered telmisartan but not valsartan inhibited the central Ang II-induced shortening of ICI without affecting the blood pressure.
Concluding message
Central Ang II system is involved in the facilitation of micturition reflex through the CRF1 receptor in rats. Peripherally administered AT1 receptor antagonist telmisartan inhibits the central Ang II induced facilitation of micturition reflex. The central AT1 receptors might be possible therapeutic targets against psychological stress-induced frequent urination.
Figure 1
Figure 2
References
  1. Bali A and Jaggi AS. Angiotensin as stress mediator: role of its receptor and interrelationships among other stress mediators and receptors. Pharmacol Res. 2013; 76:49-57.
  2. Kawamoto B, Shimizu S, Shimizu T et al. Angiotensin II centrally induces frequent detrusor contractility of the bladder by acting on brain angiotensin II type 1 receptors in rats. Sci Rep. 2016; 6:22213.
  3. Kume K, Hanyu H, Sakurai H et al. Effects of telmisartan on cognition and regional cerebral blood flow in hypertensive patients with Alzheimer's disease. Geriatr Gerontol Int. 2012; 12(2):207-14.
Disclosures
Funding JSPS KAKENHI Grant [no. 17K16797 (SS)] and 12th Japanese Urological Association Young Research Grant (SS). Clinical Trial No Subjects Animal Species Rat Ethics Committee The Animal Ethics Committee of Kochi University