AB302. SPR-29 Sphingosine-1-phosphate in vitro and in vivo modulates corpus cavernosum smooth muscle tone

OBJECTIVE: The bioactive lipid sphingosine-1-phosphate (S1P) regulates smooth muscle (SM) contractility predominantly via three G protein-coupled receptors. The S1P1 receptor is associated with nitric oxide-mediated SM relaxation while S1P2 & S1P3 receptors are linked to SM contraction via activation of the Rho-kinase (ROK) pathway. The objective of this study was to determine the role of S1P in the modulation of corpus cavernosum (CC) SM (CCSM) tone. METHODS: Human and rat samples were used. Plasma S1P levels were detected by high-performance liquid chromatography. The expression of S1P1-3 receptors and sphingosine kinase-1 (SphK1) was determined by real-time RT-PCR and western blot. In vitro organ bath contractility and in vivo intracavernous pressure (ICP) measurements were performed. Results were expressed as mean ± SEM for n experiments. Statistical analysis was performed using either the Student’s t-test (when two sample treatments were being compared) or using ANOVA when multiple means were compared. P<0.05 was considered significant. RESULTS: Plasma S1P levels were determined to be ~200 nanomolar. Human and rat CC both express SphK1 and all S1P1-3 receptors. Exogenous S1P and the S1P receptor agonist FTY720-P contracted while antagonist JTE-013 relaxed CCSM in vitro. Meanwhile, force produced by S1P and agonists could be totally reversed by ROK inhibitor. Also, intracavernous injection of FTY720-P inhibited ICP rise induced by submaximal electrical stimulation of cavernous nerve, while JTE-013 alone induced ICP increase in vivo. Finally, SphK1 siRNA knocked down rat CC SphK1 by 80% and ICP were significantly potentiated. CONCLUSIONS: In conclusion, we provide novel data that S1P, possibly coupling S1P2 and S1P3 receptors via RhoA/ROK pathway, mediates CCSM in vitro and in vivo. Antagonizing S1P or its receptors induces CCSM relaxation and proerectile effects. Thus, we provide the first clear evidences that the S1P system is another key contractile regulatory system in CC and thus this pathway is a potential therapeutic target for the treatment of priapism and erectile dysfunction. FUNDING SOURCE(S): NIH R01 DK077116 to ME DiSanto