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 . Our previous reports showed that centrally administered Ang II facilitates micturition reflex via the central AT1 receptors without affecting maximum voiding pressure (MVP) . 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 , 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).
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 . 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 . 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 . A clinical study showed that telmisartan has beneficial effects on cognitive and regional cerebral blood flow in elderly hypertensive patients with Alzheimer’s disease . 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.