The effects of (+/-)-, (+)-, and (-)-atenolol, sotalol, and amosulalol on the rat left atria and portal vein.

The effects of (+/-)-, (+)-, and (-)-atenolol, sotalol, and amosulalol alone on the rat left atria and portal vein and on the respective beta 1- and beta 2-adrenoceptor-mediated responses to isoprenaline have been determined. (+/-)-Atenolol at 10(-6) M had no effect whereas high concentrations of (+/-)- and (-)-sotalol, 10(-5)-10(-4) M, and (+/-)-, and (-)-amosulalol depressed the response of the rat left atria to cardiac stimulation which indicates membrane stabilizing activity. None of the drugs tested had any effect alone on the rat portal vein. The order of potency as antagonists was (+/-)-amosulalol > (+/-)-atenolol > (+/-)-sotalol at beta 1-adrenoceptors and (+/-)-amosulalol > (+/-)-sotalol > (+/-)-atenolol at beta 2-adrenoceptors. (+/-)-Atenolol and (+/-)-amosulalol are beta 1-selective whereas (+/-)-sotalol is beta 2-selective. For each of the racemic beta-blockers, the beta 1- and beta 2-adrenoceptor blocking activity was predominantly due to the (-)-enantiomer.