[Interaction of the inotropic effect of norepinephrine and acetylcholine on the guinea pig's myocardium].

The experiments on guinea pig myocardium slices have been carried out to study the interaction of inotropic effects of different doses of norepinephrine (NE, from 10(-7) to 10(-5) mol/l) and acetylcholine (AC, from 10(-8) to 10(-6) mol/l). With an increase of NE concentration the negative influence of AC on the inotropic action is replaced by positive one. It is shown that there are optimal concentrations of NE and AC to exert a negative influence of AC on adrenergic inotropic effect (in these experiments--3 x 10(-7) mol/l for both influences). A decrease in frequency of contractions of AC on NE effect and positive influence of adrenergic myocardium stimulation on inotropic effect of AC, respectively. Such a type of relation of cardial effects of choline- and adrenergic influences is suggested to be designated by term "negatively accentuative antagonism" unlike the opposite type of choline-adrenergic interaction--"positive accentuative antagonism", under which AC increases inotropic effect of adrenergic myocardium stimulation, while adrenergic positive inotropic influences decrease AC effect.