V.N. Yartsev - Ph.D. (Biol.), Senior Research Scientist, Pavlov Institute of Physiology, Russian Acad. Sci., Saint-Petersburg, Russia. E-mail: yartsev@infran.ru M.V. Sviridenko - Senior Assistant, Pavlov Institute of Physiology, Russian Acad. Sci., Saint-Petersburg, Russia. E-mail: yartsev@infran.ru

Mechanisms of the blood flow redistribution during muscular work are not currently well understood. Specifically, strenuous exercise is characterized by low pH [1], high level of nitric oxide (NO) [2], and noradrenaline (NA) [3] in the blood, but the data concerning the combined effect of all these factors on the neurogenic tone of the blood vessels, are lacking. We performed this study in order to get the data indicated. As in our previous work related to the combined effect of the acidosis, NA, and cooling on the neurogenic tone of the blood vessels [4], the experiments were carried out using isolated segments of the rat tail artery. Neurogenic contraction of the vessel segment was evoked by periodic electrical field stimulation (EFS) (conducted at a frequency of 3, 10, and 40 Hz every 3 min) of perivascular nerves in the vessel segment before and after addition of NA in cumulative concentration (from 0.03 μM to 10 μM). One of the three series of experiments served as a control while in the second series, 10 μM sodium nitroprusside (SNP) used as NO donor was applied 30 min before addition of NA. In the third series, solution pH was changed from 7.4 to 6.6 by CO2 bubbled through the solution. SNP was shown to diminish considerably the artery reaction to EFS of the perivascular nerves which was further decreased by the acidosis, especially at higher frequency of the EFS. At acidosis in the presence of SNP, NA-evoked potentiation of the neurogenic tone produced by 3 Hz EFS at low NA concentration (0.03-0.1 μM) was smaller than in the presence of SNP without acidosis and in the control (Fig. 1). In the presence of SNP and acidosis, potentiative effect of the high concentration of NA (0.5-1.0 μM) on the neurogenic tone at all frequencies (besides 3 Hz at 0.5 μM NA) was significantly more pronounced than in the presence of SNP without acidosis and in the control. At acidosis in the presence of SNP, NA-evoked potentiation of the neurogenic tone produced by high frequency EFS (10-40 Hz) was significantly larger than produced by 3 Hz EFS, while in control the potentiation was almost the same at all frequencies (Fig. 2). We believe that the increased NA-evoked potentiation of the neurogenic constriction of the rat tail artery shown in our experiments at acidosis in the presence of NO at higher EFS frequencies and NA concentrations may be of importance for the blood flow redistribution in favor of vital organs at strenuous exercise.

 

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