Atypical beta-adrenoceptor subtypes mediate relaxations of rabbit corpus cavernosum
Abstract
This study was performed to characterize the beta-adrenoceptor population in rabbit isolated corpus cavernosum (RbCC) by using nonselective and selective beta-adrenoceptor agonists and antagonists in functional assays. Metaproterenol, ritodrine, fenoterol, and 8-hydroxy-5-[(1R)-1-hydroxy-2-[N-[(1R)-2-(rho-methoxyphenyl)-1-methylethyl]amino]ethyl]carbostyril (TA 2005) (3-100 nmol each) dose dependently relaxed the RbCC preparations. These relaxations were markedly reduced by N(omega)-nitro-L-arginine methyl ester (L-NAME; 10 microM) and 1H-[1,2,4]-oxadiazolo-[4,3,-a]quinoxalin-1-one (ODQ) (10 microM), whereas the adenylyl cyclase inhibitor SQ 22,536 [9-(2-tetrahydrofuryl) adenine] (10 microM) had no effect. In contrast, neither L-NAME nor ODQ affected the isoproterenol-induced RbCC relaxations, but SQ 22,536 abolished this response. Sildenafil (1 microM) significantly potentiated the relaxations induced by beta(2)-agonists without affecting the isoproterenol-evoked relaxations. Rolipram (10 microM) enhanced the relaxations elicited by isoproterenol but had no effect on those induced by the selective beta(2) agonists. Propranolol and (+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride (ICI 118,551) determined a rightward shift in the concentration-response curves to isoproterenol in a noncompetitive manner with a reduction of maximum response at the highest antagonist concentration, with the slope values significantly different…
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