Functional bombesin receptors in urinary tract of rats and human but not of pigs and mice, an in vitro study F. Aura Kullmann ⇑ , David McKenna, Grace I. Wells, Karl B. Thor Urogenix Inc./Astellas, 801 Capitola Dr., Durham, NC, USA article info Article history: Received 30 May 2013 Accepted 26 August 2013 Available online 5 September 2013 Keywords: Bladder strips Neuromedin B Gastrin-releasing peptide Electric field stimulation abstract Aims: Bombesin receptors (BB receptors) and/or bombesin related peptides are expressed in the lower urinary tract, though their function and distribution in different species is largely unknown. This study examines whether BB receptor agonists can contract bladder smooth muscle in rats, mice, pigs and humans. Methods: Bladder strips were placed in tissue baths for in vitro contractility. Neuronally evoked contrac- tions were elicited using electric field stimulation (EFS). Effects of the BB receptor agonists, neuromedin B (NMB; BB1 receptor agonist) and gastrin-releasing peptide (GRP; BB2 receptor agonist) on baseline tone and EFS-induced contractions were monitored. Results: In rat and human bladder strips, NMB and GRP (10 11 –10 6 M) increased EFS-induced contrac- tions in a concentration dependent manner. In these species, NMB and GRP also increased baseline ten- sion. In mouse and pig bladder strips, NMB and GRP (10 8 –3  10 6 M) had no effects on either parameter. Conclusions: These data suggest that bombesin receptors BB receptor 1 and/or BB receptor 2 increase bladder contractions in rat and human. The site of action of these receptors may be pre- and/or post-syn- aptic, increasing release of transmitters or enhancing smooth muscle excitability, respectively. Thus, BB1 receptor and/or BB2 receptor may offer therapeutic targets for voiding dysfunction associated with impaired bladder contractility; however, species differences must be considered when studying these receptors. Conclusions: Part of this work was published in an abstract form at the SFN meeting New Orleans, 2012. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Voiding dysfunctions associated with incomplete bladder emp- tying are common in elderly, diabetic and other patient popula- tions and can lead to symptoms such as frequency, urgency and nocturia (Andersson, 2010; Smith, 2010). Current pharmacother- apy is aimed at increasing bladder contraction work and includes bethanechol (muscarinic receptor agonist) and distigmine (acetyl- cholinesterase inhibitor). However, the efficacy of these drugs is minimal and their usage is limited due to adverse effects associ- ated with the use of parasympathomimetics that restrict their clin- ical effectiveness (Barendrecht et al., 2007). Thus, better therapeutic agents that enhance bladder contractility with mini- mal side effects are desirable. Bombesin receptors (BB receptors) are a family of G-protein coupled receptors comprised of three subtypes, BB 1,2,3 receptor activated by the endogenous peptides neuromedin B (NMB) and gastrin-releasing peptide (GRP). BB1 receptors are preferentially activated by NMB, BB2 receptors are preferentially activated by GRP and BB3 receptors may be activated by high concentrations of either peptide (Jensen et al., 2008). The peptides and their recep- tors are distributed throughout the periphery (e.g. gastrointestinal tract) and CNS and have been implicated in various functions rang- ing from urogenital and gastrointestinal smooth muscle contrac- tion via direct peripheral action, to food intake, pain, stress and fear responses via the CNS (Jensen et al., 2008)(Arora and Anubh- uti, 2006; Guan et al., 2011; Majumdar and Weber, 2012; Merali et al., 1999; Weigert et al., 1996; West and Mercer, 2005). In the lower urinary tract (LUT), immunohistochemistry and/or receptor binding studies showed expression of BB receptors and/or bombe- sin peptides in the bladder, urethra and pelvic ganglia of rat and/or guinea pig and in the intramural ganglia of the human male uri- nary bladder (Dalsgaard et al., 1983; Dixon et al., 1997; Keast and Chiam, 1994; Kilgore et al., 1993; Radziszewski et al., 1996) (Bitar and Coy, 1992)(Ghatei et al., 1985). Functional studies showed that bombesin and/or bombesin related peptides contract rat, guinea pig and human bladder smooth muscle in vitro (Maggi et al., 1992; Rouissi et al., 1991; Watts and Cohen, 1991) (Mizrahi 0143-4179/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.npep.2013.08.003 ⇑ Corresponding author. Tel.:+1 919 923 9248. E-mail addresses: aura240@yahoo.com, aura.kullmann@gmail.com (F.A. Kull- mann). Neuropeptides 47 (2013) 305–313 Contents lists available at ScienceDirect Neuropeptides journal homepage: www.elsevier.com/locate/npep