Small vessel responses of the rabbit ear

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Abstract
Blood pressures were recorded continuously from small arteries and veins of the rabbit ear by inserting 0.1 mm o.d. glass cannulae through the dorsal skin into the lumen of 0.3–0.5 mm diameter vessels. The cannulae did not occlude the lumen of the vessels. Stimulation of the third cervical nerve produced an elevation in small artery pressure, and an abrupt fall in small vein pressure with little evidence of increased small vein resistance. Stimulation of the cervical sympathetic trunk produced a marked decrease in small artery pressure. Pulsations ceased and the small arteries became bloodless. The small vein pressure exhibited an evanescent rise followed by a gradual fall. Mechanical occlusion of the macroscopically visible small veins enhanced the initial elevation in small vein pressure in response to stimulation of the sympathetic trunk. With reduced body temperature and the same degree of mechanical occlusion a maintained elevation of small vein pressure occurred throughout the entire stimulation period. This can be interpreted as the result of constriction of the small vein walls upon a column of blood held static in the occluded vein.