Function of beta1-adrenoceptors and mRNA expression of beta1- and beta2-adrenoceptors in guinea-pig esophagus

Abstract

beta-Adrenoceptor subtypes mediating relaxation were examined by using pharmacological and molecular analyses in guinea-pig esophageal muscularis mucosae. (-)-Isoprenaline-induced relaxations were antagonized by (+/-)-propranolol (pA2 = 8.47+/-0.07), a selective beta1-adrenoceptor antagonist, (+/-)-2-hydroxy-5-[2-[[2-hydroxy-3-[4-[1-methyl-4-(trifluoromethyl)-1H-imidazol-2-yl]phenoxy]propyl]amino]ethoxy]-benzamide methanesulfonate (CGP20712A; pA(2)=9.43+/-0.09), and a selective beta(2)-adrenoceptor antagonist, (+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride (ICI-118,5511; pA2 = 7.11+/-0.04), indicating that beta(1)-adrenoceptors but not beta2- or beta3-adrenoceptors were essentially involved in beta-adrenoceptor-mediated relaxations. However, the expression of messenger RNA (mRNA) for beta1- and beta2-adrenoceptors, but not for beta3-adrenoceptors, was detected by reverse transcription-polymerase chain reaction (RT-PCR). These results clearly suggest that not all beta-adrenoceptor mRNA expressed strictly reflect functional receptors in guinea-pig esophageal muscularis mucosae.