Prostatic relaxation induced by agmatine is decreased in spontaneously hypertensive rats

OBJECTIVES To compare agmatine-induced prostatic relaxation in hypertensive and control rats. To investigate the responsible mechanism(s) and the role of the ATP-sensitive potassium channel. Methods Prostate strips were isolated from male spontaneously hypertensive (SH) rats and normal Wistar-Kyoto (WKY) rats for measurement of isometric tension. The strips were precontracted with 1 Âμmol/L phenylephrine or 50 mmol/L KCl. Dose-dependent relaxation of the prostatic strips was studied by cumulative administration of agmatine, 1 to 100 Âμmol/L, into the organ bath. Effects of specific antagonists on agmatine-induced relaxation were studied. Western blotting analysis was used to measure the gene expression of the ATP-sensitive potassium channel in the rat prostate. Results Prostatic relaxation induced by agmatine was markedly reduced in SH rats compared with WKY rats. The relaxation caused by agmatine was abolished by BU224, a selective imidazoline I₂-receptor antagonist, but was not modified by efaroxan at a dose sufficient to block imidazoline I₁-receptors. The relaxation induced by diazoxide at a concentration sufficient to activate ATP-sensitive potassium channels was markedly reduced in the SH rat prostate. Expressions of ATP-sensitive potassium channel sulphonylurea receptor and inwardly rectifying potassium channel (Kir) 6.2 subunits were both decreased in the prostate of SH rats. CONCLUSION The decrease of agmatine-induced prostatic relaxation in SH rats is related to the change in ATP-sensitive potassium channels.