[Effect of elevated systemic arterial pressure on neurogenic vasoconstriction in the microcirculatory bed of rat skeletal muscles].

Vasomotor reactions produced by electrical stimulation of the sympathetic tract were studied in anesthetized rats by intravital microscopy of the skeletal muscle (extensor hallucis proprius). Experiments were made in normal and elevated blood pressure. The stimulation itself did not change BP but led to an appreciable decrease in the initial diameter of the arterioles (28.6 +/- 1.4 m). The constriction amounted to 21%. The lumen decreased by 38.9%. Injection of felypressin (Sandoz) in a dose of 6 to 8 IU/100 g produced the pressor reaction. The 27.4% rise of BP during primary phase of the pressor response inhibited the development of the neurogenic vasoconstriction which was 11.5% for arteriolar diameter and 20.4% for lumen. The data suggest that inhibition of the neurogenic vasoconstriction is caused by an increase in arteriolar pressure. Consequently the elevation of intralumen pressure is considered as a protective mechanism of the drop of the tissue blood flow because of the sympathetic vasoconstriction.