Abstract
Blood flow and heat loss characteristics of peripheral areas, such as the hand, change with continuous exposure to cold. In man, blood flow and heat loss from the hand in general indicate less vasoconstriction and greater heat loss at temperatures of 1-5° in cold-adapted persons (1). In the rabbit ear, it has been shown that the relation of thermal conductance to blood flow is temperature dependent (2); that the cold exposures alter the response of the ear circulation to norepinephrine (less change in blood flow and ear temperature) (3), although this effect appears only at higher skin or blood temperatures (5); and that the precooling of arterial blood during its flow from the interior to the ear surface in a cold environment is more marked in cold-adapted animals than warm-adapted (4). The investigation described in this paper is concerned with the heat transfer from the rabbit ear when local blood temperature is changed.
Methods. Male New Zealand, California white and Dutch-belted rabbits were used. The rabbits were kept at 3-5° for 8 weeks or more (cold-adapted, CA) and at 25° (warm-adapted, WA). Body weight and food consumption were checked twice a week. Food and water were given ad libitum.
The surgical and perfusion procedures in the experimental preparation have been described previously (5). Perfusion pressure was monitored. Blood flow was set to give an approximate blood flow of 20 ml/min·100 ml of tissue. The blood flow was measured with a drop counter.
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