β-Adrenoceptor-mediated Relaxation of Urinary Bladder Muscle in β2-Adrenoceptor Knockout Mice

Abstract

Background and Objective: In order to characterize the β-adrenoceptor (AR) subtypes involved in agonist-stimulated relaxation of murine urinary bladder we studied the effects of (-)-isoprenaline and CL 316,243 on tonic contraction and spontaneous contractions in detrusor strips of wild-type (WT) and β2-AR knockout (β2-AR KO) mice.Materials and Methods: Urinary bladders were isolated from male WT and β2-AR KO mice. β-AR subtype expression was determined with quantitative real-time PCR. Intact muscle strips pre-contracted with KCl (40 mM) were exposed to cumulatively increasing concentrations of (-)-isoprenaline or β3-AR agonist CL 316,243 in the presence and absence of the subtype-selective β-AR blockers CGP 20712A (β1-ARs), ICI 118,551 (β2-ARs), and L748,337 (β3-ARs).Results: Quantitative real-time PCR confirmed lack of β2-AR expression in bladder tissue from β2-AR KO mice. In isolated detrusor strips, pre-contraction with KCl increased basal tone and enhanced spontaneous activity significantly more in β2-AR KO than in WT. (-)-Isoprenaline relaxed tonic tension and attenuated spontaneous activity with similar potency, but the concentrations required were two orders of magnitude higher in β2-AR KO than WT. The concentration-response curves (CRCs) for relaxation were not affected by CGP 20712A (300 nM), but were shifted to the right by ICI 118,551 (50 nM) and L748,337 (10 μM). The -logEC50 values for (-)-isoprenaline in WT and β2-AR KO tissue were 7.98 and 6.00, respectively, suggesting a large receptor reserve of β2-AR. (-)-CL 316,243 relaxed detrusor and attenuated spontaneous contractions from WT and β2-AR KO mice with a potency corresponding to the drug’s affinity for β3-AR. L743,337 shifted the CRCs to the right.Conclusion: Our findings in β2-AR KO mice suggest that there is a large receptor reserve for β2-AR in WT mice so that this β-AR subtype will mediate relaxation of tone and attenuation of spontaneous activity under physiological conditions. Nevertheless, upon removal of this reserve, β3-AR can also mediate murine detrusor relaxation.

A systematic review of urinary bladder hypertrophy in experimental diabetes: Part 2. Comparison of animal models and functional consequences

“…As β‐adrenoceptor are the most important mediator of bladder smooth muscle relaxation, all of them have focused on this receptor family. Of note, bladder relaxation in humans is mediated predominantly if not exclusively by β 3 ‐adrenoceptors, whereas that in rats is a mixed response by β 2 ‐ and β 3 ‐adrenoceptors and differentially involves β 2 ‐ and β 3 ‐adrenoceptors in mice depending on the agonist being used . As these two subtypes can be differentially regulated in bladder smooth muscle, the general validity of rat and mouse studies for the human situation is unclear unless specific attempts have been made to separate the role of the two subtypes.…”

Effects of a new β3‐adrenoceptor agonist, vibegron, on neurogenic bladder dysfunction and remodeling in mice with spinal cord injury

“…22,23 Lastly, bladder muscle relaxation in the mouse is largely driven by adrenoceptors of the β2 subtype whereas, in humans, it is more dependent on the β3 subtype. 28 This difference might limit the translational impact of the study although β3 adrenoceptor activation by vibegron was effective to reduce SCI-induced DO even in the β2 adrenoceptorpredominant mouse bladder.…”

“…Thus, direct afferent nerve activity measurements during bladder filling are needed in future studies, as previous studies reported that mirabegron, another β3 agonist, can inhibit bladder afferent activity, which may be related to suppression of bladder microcontractions 22,23 . Lastly, bladder muscle relaxation in the mouse is largely driven by adrenoceptors of the β2 subtype whereas, in humans, it is more dependent on the β3 subtype 28 . This difference might limit the translational impact of the study although β3 adrenoceptor activation by vibegron was effective to reduce SCI‐induced DO even in the β2 adrenoceptor‐predominant mouse bladder.…”

Inhibition of Full Smooth Muscle Contraction in Isolated Human Detrusor Tissues by Mirabegron Is Limited to Off-Target Inhibition of Neurogenic Contractions

“…Speciesdependent differences in β-adrenergic detrusor relaxation may be imparted by divergent expression patterns of receptor subtypes, and by differences in ligand-receptor interactions (Cernecka et al, 2015;Dale et al, 2014). β-Adrenergic relaxation of human detrusor tissues has been widely attributed to β 3 , whereas β-adrenergic relaxation of detrusor tissues from mice is predominantly mediated by β 2 (Propping et al, 2016;Propping et al, 2015;Wuest et al, 2009). Data are available from wildtype and β 2 -adrenoceptor knockout mice, but obviously not from β 3 -adrenoceptor knockout mice.…”