[The effect of noradrenaline on the neurogenic vasoreactivity at various frequencies of the electrical field stimulation].

The effect of 0.03-10.0 microM noradrenaline on the response to electrical field stimulation (EFS) of the juvenile rat tail artery segment was studied. At frequencies of the EFS equal to 10 or 40 Hz, noradrenaline was shown to cause much more pronounced potentiation or--at higher concentration--much less pronounced inhibition of the EFS-evoked constriction in arteries characterized by spontaneous decrease in the constriction value in the course of experiments as compared with arteries which were not characterized by such a decrease. At frequencies of the EFS equal to 3 or 5 Hz, the value and/or direction of the change in the neurogenic vasoconstriction in the presence of noradrenaline depends on the presence of the spontaneous decrease in the constriction evoked by EFS at 10 Hz, rather than at 3 or 5 Hz. It is concluded that the character of the change in the neurogenic vasoreactivity is a factor of a great importance for the prediction of the further change in the reactivity in the presence of noradrenaline.