Effects of low tissue temperature on peripheral vascular control mechanisms.

Influence of low temperatures on vascular effects produced adrenaline, noradrenaline and vasoconstrictor nerve stimulation was studied in the feet of ducks. Observations were made on isolated preparations as well as on intact ducks with one or both feet immersed in ice-water. Isolated preparations were perfused with physiological solution and information on changes in vascular resistance obtained by direct measurement of flow changes during perfusion at constant pressure or by measuring changes in perfusion pressure during perfusion at constant flow. In intact ducks changes in blood flow were recorded as changes in digital subcutaneous tissue temperature. The study revealed that in the duck foot a relatively large fraction of the resistance to blood flow is found in the arteries of the proximal part of the foot. During cooling of the foot the influence of vasoconstrictor nerve stimulation and low doses of adrenaline and noradrenaline on vascular resistance is gradually lost, and it is negligible at temperatures below 8 degrees C. At these low temperatures the blood vessels stay dilated and blood flow through the web seems to be determined by the digital arterial blood pressure.