The influence of prior cold exposure on vasoconstriction induced by abrupt cold exposure has been studied in the rabbit ear. Dutch breed rabbits were individually caged outdoors (maximum temperature, 21° C; minimum, -7° C; average, 5. 9° C) and a control group was kept at 27° C over a five month period. Three groups of New Zealand rabbits were divided to be exposed to 27° C, 5° C, and 5° C day and 27° C night temperatures.
Rectal, ear and body surface temperatures, heat loss from the ear, and blood flow in the ear were recorded at 27° C, 23° C and 5° C. In general, at 23°and 27° C there was no difference between the groups of rabbits. After one hour exposure to 5° C, outdoor and 5° C groups had a low blood flow to the ear and had no decline in rectal temperature. Other groups, however, had a decrease in rectal temperature and higher ear blood flow. After 12 to 18 hours exposure to 5° C, rectal temperature. returned to original values in the 27° C animals; blood flow to the ear decreased slightly. Ear blood flow in outdoor and 5° C rabbits increased during this period.