Unknown

Effects of optical isomers of methylephedrine (MEP) on the spontaneous beating rate of isolated right atrium of normal and reserpinized rat were investigated to assess direct and indirect actions on beta 1-adrenoceptors. l-MEP (10(-5) - 3 x 10(-4) M) showed slight increase in heart rate. In addition, d-MEP (3 x 10(-5) - 3 x 10(-4) M) caused a decrease in heart rate. Positive chronotropic effects of l-MEP was attenuated by pretreatment with atenolol ( a selective beta 1-adrenoceptor antagonist) or reserpine treatment (8 mg/kg, s.c.). l-MEP has beta 1-adrenoceptor agonist activity, while d-MEP is suggested to have only low or no affinity for beta 1-adrenoceptors. The relatively weak activity of l-MEP is believed to be mainly mediated by released noradrenaline.