β2-adrenoceptor-mediated inhibition of field stimulation induced contractile responses of the smooth muscle of the rat prostate gland

Isolated preparations of rat prostate responded to electrical field stimulation (2 strains every 60 s, 0.5 ms, 10 Hz, 80 V) with contractions. The adrenoceptor agonists adrenaline, isoprenaline and noradrenaline (0.1 nM-10 muM) elicited concentration-dependent inhibition of electrical field stimulation-induced contractions of the rat prostate. Phenylephrine had no effect on the amplitude of electrical field stimulation-induced contractions. The rank order of potency was isoprenaline greater than or equal to adrenaline = noradrenaline > phenylephrine. Inhibition of electrical field stimulation-induced contractions by isoprenaline was attenuated by propranolol (1 muM). The selective beta (1)-adrenoceptor agonist (-)-1-(3,4-dimethoxy-phenethylamino)-3-(3,4-dihydroxyphenoxy)-2-propanol)oxalate (RO363) and the selective beta (2)-adrenoceptor agonist salbutamol (1 nM-100 muM) were approximately equipotent in inhibiting electrical field stimulation-induced contractions but the selective beta (3)-adrenoceptor agonist sodium 4-(2-[2-hydroxy-{3-chlorophenyl}ethylamino]propyl)phenoxyacetate (BRL 37344, 1 nM-100 muM) did not inhibit electrical field stimulation-induced contractions. The selective beta (2)-adrenoceptor antagonist, (+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol (ICI 118 551, 0.1 muM) attenuated inhibitory responses to isoprenaline and salbutamol, while the selective beta (1)-adrenoceptor antagonist atenolol (3 muM) did not. Contractions induced by electrical field stimulation were also inhibited by forskolin (10 nM-3 mM) but unaffected by sodium nitroprusside (10 nM-1 mM) indicating the presence of an inhibitory cAMP mechanism. These data suggest that stimulation of beta (2)-adrenoceptors can inhibit contractions of the rat prostate induced by electrical field stimulation. (C) 2001 Elsevier Science B.V. All rights reserved.