[An analysis of the components of the hyperosmotic vasomotor effect]

The vessels of the rats hindlimbs were perfused by the Tyrode solution with the constant outflow. The efficacy of vasoconstrictor effects produced by short-time infusion of exogenous norepinephrine or by the electrostimulation of sympathetic chain while increasing osmotic pressure of the perfusion solution was studied. The hyperosmolarity suppressed both vasoconstrictory reactions, but in the different degree and velocity. The comparison of osmolarity effects on maximally relaxed and precontracted vessels permitted distinguishing several phases of the reaction. It can be supposed that an increase in osmolarity of the blood flowing induced a decrease in the vascular wall sensitivity to the vasoconstrictor effects of norepinephrine followed by depression of norepinephrine secretion from nerve terminals. The relationship of these compounds determines vasomotor response to an increase of osmolarity in different moments of time.