Urothelial beta-3 adrenergic receptors in the rat bladder.

AIMS: To investigate the distribution of beta-3 adrenergic receptors (ß(3)ARs) in the rat bladder and to examine the contribution of urothelial ß(3)ARs to agonist-induced suppression of bladder reflexes and relaxation of smooth muscle. METHODS: Bladder tissue was collected from 8- to 10-month old female SD rats. In some samples, the urothelium was surgically separated from the smooth muscle. The expression and localization of ßAR mRNA and ß(3)AR protein were determined using RT-PCR and immunohistochemistry. Contractile responses to the specific ß(3)AR agonists TAK-677 and BRL37344 were measured in bladder strips with or without the urothelium. The contribution of urothelial ß(3)ARs to the micturition reflex was assessed in continuous cystometry in urethane anesthetized rats using intravesical delivery of ß(3)AR agonists. RESULTS: RT-PCR detected mRNA of all ßARs in urothelium and smooth muscle. Immunostaining detected ß(3)ARs throughout the urothelium, in the smooth muscle, myofibroblast-like cells, and in the peripheral nerves. Ovariectomy did not change the distribution of ß(3)ARs in any bladder structure. Intravesical administration of TAK-677 and BRL37344 (1-5 × 10(-4) M) decreased voiding frequency and amplitude of bladder contractions. In bladder strips in vitro both ß(3)AR agonists (10(-12) to 10(-4) M) relaxed the smooth muscle in a concentration-dependent manner to the same extent in strips with and without the urothelium. CONCLUSIONS: In addition to their presence in bladder smooth muscle, ß(3)ARs are present in the urothelium where their activation may alter reflex voiding via release of factor(s) that act on non-myocyte structures including the afferent and/or efferent nerves to influence bladder contractility.

Effects of beta3-adrenergic receptor activation on rat urinary bladder hyperactivity induced by ovariectomy.

Voiding dysfunctions, including increased voiding frequency, urgency, or incontinence, are prevalent in the postmenopausal population. Beta(3)-adrenergic receptor (beta(3)AR) agonists, which relax bladder smooth muscle, are being developed to treat these conditions. We utilized the rat ovariectomy (OVX) model to investigate the effect of ovarian hormone depletion on bladder function and the potential for beta(3)AR agonists to treat bladder hyperactivity in this setting. OVX increased voiding frequency and decreased bladder capacity by approximately 25% in awake rats and induced irregular cystometrograms in urethane-anesthetized rats. Reverse transcription-polymerase chain reaction revealed three betaARs subtypes (beta(1,2,3)) in bladder tissue, and immunostaining indicated beta(3)AR localization in urothelium and detrusor. Receptor expression was not different in OVX and SHAM rats. The beta(3)AR agonist selectivity of BRL37344 [(+/-)-(R(*),R(*))-[4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]phenoxy]acetic acid sodium hydrate], TAK-677 [(3-((2R)-(((2R)-(3-chlorophenyl)-2-hydroxyethyl)amino)propyl)-1H-indol-7-yloxy)acetic acid], and FK175 [acetic acid, 2-[[(8S)-8-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino]-6,7,8,9-tetrahydro-5H-benzocyclohepten-2-yl]oxy], ethyl ester, hydrochloride] was confirmed by examining the relative potency for elevation of cAMP in CHOK1 cells overexpressing the various rat betaARs. Intravenous injection of each of the beta(3)AR agonists (0.1-500 microg/kg) in anesthetized rats decreased voiding frequency, bladder pressure, and amplitude of bladder contractions. In bladder strips, beta(3)AR agonists (10(-12)-10(-4) M) decreased baseline tone and reduced spontaneous contractions. BRL37344 (5 mg/kg) and TAK-677 (5 mg/kg) injected intraperitoneally in awake rats decreased voiding frequency by 40 to 70%. These effects were not altered by OVX. The results indicate that OVX-induced bladder dysfunction, including decreased bladder capacity and increased voiding frequency, is not associated with changes in beta(3)AR expression or the bladder inhibitory effects of beta(3)AR agonists. This suggests that beta(3)AR agonists should prove effective for the treatment of overactive bladder symptoms in the postmenopausal population.