Chronotropic effects of optical isomers of ephedrine and methylephedrine in the isolated rat right atria and in vitro assessment of direct and indirect actions on beta 1-adrenoceptors

Biological & Pharmaceutical Bulletin
T KawasujiH Saito

Abstract

Effects of optical isomers of ephedrine (EPH) and 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-EPH (3 x 10(-7) - 3 x 10(-5) M) and d-EPH (10(-6) - 10(-4) M) markedly increased beating rate of rat right atrium. l-MEP (10(-5) - 3 x 10(-4) M) showed slight increase in heart rate. The potency of positive chronotropic effect is l-EPH > d-EPH "l-MEP. l-EPH was about 3 times as potent as d-EPH. In addition, d-MEP (3 x 10(-5) - 3 x 10(-4) M) caused a decrease in heart rate. Positive chronotropic effects of EPH isomers and l-MEP were attenuated by pretreatment with atenolol ( a selective beta 1-adrenoceptor antagonist) or reserpine treatment (8 mg/kg, s.c.). In reserpinized atria, the maximal increase by d-EPH was quite small, and l-MEP decreased heart rate. On the other hand, d-MEP, at 3 x 10(-4) M, did not show antagonist activity against the positive chronotropic effect of isoprenaline (10(-10) - 10(-5) M). These results suggest that l-EPH, d-EPH and l-MEP have beta 1-adrenoceptor agonist activity, while d-MEP is suggested to have only low or no affinity for beta 1-adrenoceptors. The rela...Continue Reading

Citations

Nov 14, 2006·British Journal of Pharmacology·J T LilesP J Kadowitz
Oct 6, 2005·Life Sciences·Richard B Rothman, Michael H Baumann
Nov 11, 2003·Canadian Journal of Physiology and Pharmacology·Paul A DabischPhilip J Kadowitz
Jan 31, 2003·Synapse·Paul J WellmanDao H Ho
Nov 14, 2006·British Journal of Pharmacology·J R Docherty
Apr 5, 2007·The Journal of Pharmacology and Experimental Therapeutics·Guoyi MaDennis R Feller
Jul 9, 2005·The Journal of Pharmacology and Experimental Therapeutics·John T LilesPhilip J Kadowitz
Feb 2, 2018·Biological & Pharmaceutical Bulletin·Hiroaki TakemotoYoshinori Kobayashi
Feb 20, 2018·European Journal of Pharmacology·Hadeel A Alsufyani, James R Docherty

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