Muscarinic receptor subtypes and signaling involved in the attenuation of isoprenaline-induced rat urinary bladder relaxation

Depts. of Pharmacology and Pharmacotherapy and of Urology, Academic Medical Center, Amsterdam, The Netherlands.
Archiv für Experimentelle Pathologie und Pharmakologie (Impact Factor: 2.47). 09/2011; 384(6):555-63. DOI: 10.1007/s00210-011-0689-8
Source: PubMed


β-Adrenoceptors are important mediators of smooth muscle relaxation in the urinary bladder, but the concomitant presence of a muscarinic agonist, e.g., carbachol, can attenuate relaxation responses by reducing potency and/or efficacy of β-adrenoceptor agonists such as isoprenaline. Therefore, the present study was designed to explore the subtypes and signalling pathways of muscarinic receptors involved in the attenuation of isoprenaline-induced isolated rat detrusor preparations using novel subtype-selective receptor ligands. In radioligand binding studies, we characterized BZI to be a M(3)-sparing muscarinic agonist, providing selective M(2) stimulation in rat bladder, and THRX-182087 as a highly M(2)-selective antagonist. The use of BZI and of THRX-182087 in the presence of carbachol enabled experimental conditions with a selective stimulation of only M(2) or M(3) receptors, respectively. Confirming previous findings, carbachol attenuated isoprenaline-induced detrusor relaxation. M(2)-selective stimulation partly mimicked this attenuation, indicating that both M(2) and M(3) receptors are involved. During M(3)-selective stimulation, the attenuation of isoprenaline responses was reduced by the phospholipase C inhibitor U 73,122 but not by the protein kinase C inhibitor chelerythrine. We conclude that both M(2) and M(3) receptors contribute to attenuation of β-adrenoceptor-mediated relaxation of rat urinary bladder; the signal transduction pathway involved in the M(3) component of this attenuation differs from that mediating direct contractile effects of M(3) receptors.

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Available from: Martin C Michel
    • "On the other hand, the maximum relaxation responses to isoprenaline were enhanced in both groups of rats in the presence of the M 2 -preferring antagonist methoctramine, and in the presence of methoctramine isoprenaline caused similar maximum relaxation in both groups. These findings indicate that a relatively short period of hypercholesterolemia may not affect the M 3 -mediated direct contractile responses to carbachol, but may already enhance the function of relaxation-inhibiting M 2 receptors (Witte et al. 2011), thereby indirectly impairing β-adrenoceptor-mediated detrusor relaxation. As relaxation of rat detrusor is mediated by a combination of β 2 -and β 3 -adrenoceptors, which may be regulated differently in the bladder (Michel 2014), the authors also studied relaxation by the β 2 -agonist salbutamol and the mildly β 3 -selective agonist BRL 37,344 and found that both exhibited slightly enhanced relaxation responses in the presence of methoctramine in rats with hypercholesterolemia in comparison to those without; however, these findings are difficult to interpret as responses to isoprenaline were not enhanced. "
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    ABSTRACT: Bladder dysfunction is common in the general population (Stewart et al. 2010) and even more so among patients seeing a physician for any reason (Goepel et al. 2002). It often manifests as lower urinary tract symptoms (LUTS), a term originally coined to describe voiding and storage symptoms in men with benign prostatic hyperplasia (BPH) but now more universally used to describe any type of voiding and storage symptoms in both sexes. Studies into possible causes of urinary bladder dysfunction have long focused on detrusor smooth muscle cells (Turner and Brading 1999). More recently, it became clear that several other types of cells and organs contribute to regulating detrusor smooth muscle function. These include the urothelium (Andersson and McCloskey 2014; Michel 2015), afferent nerves (Michel and Igawa 2015; Yoshimura et al. 2014b), and the central and autonomic nervous systems (Fowler and Griffiths 2010; Yoshimura et al. 2014a). Alterations in any of these may at least partly be responsible for detrusor dysfunction and, accordingly, be potential targets for the treatment of bladder dysfunction. As highlighted by an article in this issue of Naunyn-Schmiedeberg's Archives of Pharmacology (Bayrak et al. 2015), there is an additional suspect, the bladder vasculature. This article will discuss the currently available experimental and clinical evidence for a role of the vasculature in causing bladder dysfunction, and how existing and emerging treatments may modulate bladder function by acting on blood vessels. Due to a similarity in concept, data on prostate perfusion will also be discussed to some extent.
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    • "the same has been found, although there is some evidence to suggest that stimulation of ␤ 2 -adrenoceptors might also play a role [10–12]. There is also evidence to suggest that there is crosstalk between the parasympathetic and sympathetic systems as stimulation of postjunctional M2 receptors has been shown to inhibit ␤ 3 -adrenoceptor induced relaxation [13] [14]. While the ␤-adrenoceptor subtypes involved in direct smooth muscle relaxation have been clearly identified, very little has been done to investigate the identity, function and particularly the location of ␤-adrenoceptors that affect neurogenic contractions of the bladder. "
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    ABSTRACT: Activation of β3-adrenoceptors has been shown to have a direct relaxant effect on urinary bladder smooth muscle from both rats and humans, however there are very few studies investigating the effects of β3-adrenoceptor agonists on nerve-evoked bladder contractions. Therefore in the current study, the role of β3-adrenoceptors in modulating efferent neurotransmission was evaluated. The effects of β3-adrenoceptor agonism on neurogenic contractions induced by electrical field stimulation (EFS) were compared with effects on contractions induced by exogenous acetylcholine (Ach) and αβ-methylene adenosine triphosphate (αβ-meATP) in order to determine the site of action. Isoproterenol inhibited EFS-induced neurogenic contractions of human bladder (pD2=6.79; Emax=65%). The effect of isoproterenol was selectively inhibited by the β3-adrenoceptor antagonist L-748,337 (pKB=7.34). Contractions induced by exogenous Ach (0.5-1μM) were inhibited 25% by isoproterenol (3μM) while contractions to 10Hz in the same strip were inhibited 67%. The selective β3-adrenoceptor agonist CL-316,243 inhibited EFS-induced neurogenic contractions of rat bladder (pD2=7.83; Emax=65%). The effects of CL-316,243 were inhibited in a concentration dependent manner by L-748,337 (pA2=6.42). Contractions induced by exogenous Ach and αβ-meATP were significantly inhibited by CL-316,243, 29% and 40%, respectively. These results demonstrate that the activation of β3-adrenoceptors inhibits neurogenic contractions of both rat and human urinary bladder. Contractions induced by exogenously applied parasympathetic neurotransmitters are also inhibited by β3-agonism however the effect is clearly less than on neurogenic contractions (particularly in human), suggesting that in addition to a direct effect on smooth muscle, activation of prejunctional β3-adrenoceptors may inhibit neurotransmitter release.
    Full-text · Article · Dec 2013 · Pharmacological Research
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    • "Other potential effects of β 3 -adrenoceptor agonists on bladder function should also be considered. For example, there is an interaction between muscarinic and β-adrenergic systems in the bladder (Witte et al. 2011), which may be important pathophysiologically when acetylcholine is released non-neuronally during the storage phase but also therapeutically if a combination treatment of muscarinic antagonists and β-adrenergic agonists is being considered. In this regard, we are still trying to understand why some muscarinic antagonists exhibit a certain degree of bladder selectivity (Yamazaki et al. 2011), and it is largely unknown whether a similar phenomenon exists for β 3 -adrenoceptor agonists. "
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    ABSTRACT: 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.
    Preview · Article · Dec 2012 · Archiv für Experimentelle Pathologie und Pharmakologie
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