Pulmonary, Gastrointestinal and Urogenital Pharmacology Thromboxane A 2 induces contraction of human prostate smooth muscle by Rho kinase- and calmodulin-dependent mechanisms Frank Strittmatter a,b , Christian Gratzke a, ⁎, Philipp Weinhold a , Christian J. Steib c , Anna C. Hartmann c , Boris Schlenker a , Karl-Erik Andersson d , Petter Hedlund b,e , Christian G. Stief a , Martin Hennenberg a a Department of Urology, University of Munich, Munich, Germany b Department of Clinical and Experimental Pharmacology, Lund University, Sweden c Department of Medicine II, University of Munich, Munich, Germany d Wake Forest Institute for Regenerative Medicine, Winston-Salem, NC, USA e Urological Research Institute, San Raffaele University, Milan, Italy abstract article info Article history: Received 21 June 2010 Received in revised form 4 October 2010 Accepted 16 October 2010 Available online 31 October 2010 Keywords: Benign prostate hyperplasia Lower urinary tract Lower urinary tract symptoms Smooth muscle Thromboxane A 2 U46619 Thromboxane A 2 (TXA 2 ) induces contraction in different smooth muscle types via its receptor (TXA 2 receptor). However, any motoric role of TXA 2 in prostate smooth muscle tone has not been studied to date. Here, we investigated whether TXA 2 induces contraction of human prostate tissue. After ethical approval, prostate tissue was obtained from 47 patients undergoing radical prostatectomy. Effects of the TXA 2 analogue U46619 ((5Z)-7-[(1R,4S,5S,6R)-6-[(1E,3S)-3-hydroxy-1-octenyl]-2-oxabicyclo[2.2.1]hept-5-yl]-5-heptonic acid) in isolated human prostate strips were studied in organ bath experiments with or without the Rho kinase inhibitor, Y27632 (trans-4-[(1R)-1-aminoethyl]-N-4-pyridinylcyclohexanecarboxamide dihy- drochloride), or the calmodulin antagonist W7 (N-(6-aminohexyl)-5-chloro-1-naphtalenesulfonamide hydrochloride). Expression of TXA 2 synthase and TXA 2 receptors were examined by Western blot analysis and immunohistochemistry. Endogenous TXA 2 was quantified by enzyme immunoassay. U46619 induced concentration-dependent contractions of human prostate strips, with a maximum contraction at 3 μM. U46619-induced prostate contraction was significantly inhibited by Y27632 (30 μM) and by W7 (100 μM). TXA 2 synthase and TXA 2 receptors were detected by Western blot analysis. Immunohistochemical stainings showed that expression of TXA 2 synthase in prostate tissue was located to glandular cells, while prostate TXA 2 receptors were located to smooth muscle and glandular cells. The stable TXA 2 metabolite TXB 2 was detected by enzyme immunoassay in the prostate. TXA 2 induces contraction of isolated human prostate tissue by TXA 2 receptor activation. Prostate smooth muscle TXA 2 receptors are coupled to Rho kinase and Ca 2+ -dependent mechanisms. The distribution of TXA 2 synthase and TXA 2 receptors in the human prostate suggests TXA 2 - mediated paracrine epithelial–stromal interactions. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Prostate tone is regulated by α 1 -adrenoceptors, which induce smooth muscle contraction by activation of Rho kinase and Ca 2+ / calmodulin-dependent mechanisms in prostate smooth muscle cells (Andersson, 2007; Christ and Andersson, 2007; Schwinn and Roehr- born, 2008). In patients with benign prostate hyperplasia, prostate tone is increased and contributes to lower urinary tract symptoms besides prostate growth and other factors (Andersson et al., 1997; Michel and Vrydag, 2006). Consequently, α 1 -adrenoceptor blockers are routinely applied to patients with lower urinary tract symptoms to reduce prostate tone and urethral obstruction (Andersson, 2007; Schwinn and Roehrborn, 2008). As prostate tone represents an important target for the treatment of lower urinary tract symptoms, the mediators and principles of prostate smooth muscle contraction are of outstanding interest. In addition to adrenoceptors, Rho kinase- and Ca 2+ /calmodulin- mediated smooth muscle contraction may be induced by various other receptors and mediators (Hennenberg et al., 2008; Somlyo and Somlyo, 2000). Thromboxane A 2 (TXA 2 ) induces contraction in different smooth muscle types and organs via the TXA 2 receptor (“TP receptor”)(Huang et al., 2004; Nakahata, 2008; Shen and Tai, 1998). TXA 2 is an inflammatory mediator, which is synthetized from prostaglandin H 2 (PGH 2 ) by TXA 2 synthase after the conversion of arachidonic acid to PGH 2 by cyclooxygenases (Nakahata, 2008; Shen and Tai, 1998). Smooth muscle contraction by TXA 2 involves activation of Rho kinase and Ca 2+ /calmodulin-dependent signaling (Huang et al., 2004; Nakahata, 2008; Somlyo and Somlyo, 2000). U46619 is a synthetic TXA 2 analogue, which specifically acts on TXA 2 receptors (Shen and Tai, 1998). European Journal of Pharmacology 650 (2011) 650–655 ⁎ Corresponding author. Urologische Klinik, Universitätsklinikum Großhadern, Marchioninistr. 15, 81377 München, Germany. Tel.: + 49 89 7095 0. E-mail address: christian.gratzke@med.uni-muenchen.de (C. Gratzke). 0014-2999/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ejphar.2010.10.052 Contents lists available at ScienceDirect European Journal of Pharmacology journal homepage: www.elsevier.com/locate/ejphar