Thromboxane A₂ induces contraction of human prostate smooth muscle by Rho kinase- and calmodulin-dependent mechanisms

Thromboxane A₂ (TXA₂) induces contraction in different smooth muscle types via its receptor (TXA₂ receptor). However, any motoric role of TXA₂ in prostate smooth muscle tone has not been studied to date. Here, we investigated whether TXA₂ induces contraction of human prostate tissue. After ethical approval, prostate tissue was obtained from 47 patients undergoing radical prostatectomy. Effects of the TXA₂ 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 dihydrochloride), or the calmodulin antagonist W7 (N-(6-aminohexyl)-5-chloro-1-naphtalenesulfonamide hydrochloride). Expression of TXA₂ synthase and TXA₂ receptors were examined by Western blot analysis and immunohistochemistry. Endogenous TXA₂ was quantified by enzyme immunoassay. U46619 induced concentration-dependent contractions of human prostate strips, with a maximum contraction at 3μM. U46619-induced prostate contraction was significantly inhibited by Y27632 (30μM) and by W7 (100μM). TXA₂ synthase and TXA₂ receptors were detected by Western blot analysis. Immunohistochemical stainings showed that expression of TXA₂ synthase in prostate tissue was located to glandular cells, while prostate TXA₂ receptors were located to smooth muscle and glandular cells. The stable TXA₂ metabolite TXB₂ was detected by enzyme immunoassay in the prostate. TXA₂ induces contraction of isolated human prostate tissue by TXA₂ receptor activation. Prostate smooth muscle TXA₂ receptors are coupled to Rho kinase and Ca²⁺-dependent mechanisms. The distribution of TXA₂ synthase and TXA₂ receptors in the human prostate suggests TXA₂-mediated paracrine epithelial–stromal interactions.