Effects of sympathetically induced vasomotion on tissue-capillary fluid exchange.

The spontaneous and rhythmic constriction of peripheral arterioles, which is not associated with the cardiac or respiratory cycles, is called vasomotion. Vasomotion is observed in various tissues of various species, but the physiological role of vasomotion has not been clarified because of the difficulty in controlling the appearance of vasomotion in in vivo preparations. We developed a method of controlling vasomotion in in vivo experiments. The electrical stimulation of the cervical sympathetic nerve could reproducibly evoke vasomotion in rabbit ear skin. The frequencies of the evoked vasomotion were 0.04-0.07 Hz, which corresponded to spontaneously occurring vasomotion that has been reported before. Vasomotion was always evoked between 25 and 35 degrees C. At lower than 17 degrees C or higher than 37 degrees C, vasomotion was not evoked. With the use of this method of evoking vasomotion in vivo, the role of vasomotion in tissue perfusion was examined. A tracer (Cr-EDTA) was injected into the ear tissue, and tracer fading was then measured by using a camera. The rates of fading (clearance) of the tracer with vasomotion were significantly greater (1.7 to 8.1 times) than those without vasomotion. These results provided evidence that vasomotion enhanced tissue perfusion.