PMID: 1143364Jan 1, 1975Paper

Frequency-dependence of the positive inotropic effect of methoxamine and naphazoline mediated by alpha-Adrenoceptors in the isolated rabbit papillary muscle

Naunyn-Schmiedeberg's Archives of Pharmacology
M Endoh, H J Schümann


Under the conditions of different stimulation frequencies the inotropic effects of the alpha-adrenoceptor stimulationg agents, methoxamine, naphazoling and oxymetazoline were studied on the isolated rabbit papillary muscle. 1. On the papillary muscle stimulated at 0.5 Hz methoxamine in concentrations from 10(-5)M caused a significant and dose-dependent positive inotropic effect. At 10(-3)M methoxamine decreased the developed tension. With increasing frequency of stimulation (0.5--1--1.5Hz), the positive inotropic effect became smaller, while the negative inotropic one was more pronounced. The time course of the disappearance of the negative inotropic effect of methoxamine by washout differed from that of the positive inotropic effect: the negative component disappeared within 30 min, whereas the positive one lasted for about 100 min. The positive inotropic effect of noradrenaline (10(-6)M), in contrast ot that of methoxamine, was not influenced by the frequency under the same conditions of stimulation. Also naphazoline (10(-5)M) caused a significant positive inotropic effect on the papillary muscle stimulated at 0.5 Hz, while oxymetazoline induced exclusively a negative inotropic effect. 2. The positive inotropic effect of meto...Continue Reading


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