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Analbuminemic rats died within 18 h after a rapid decrease of body temperature whereas control Charles River, Wistar, and Sprague Dawley rats survived for 40 h, when the animals were kept at 5 degrees C without food. Five low molecular weight fractions obtained from Sprague Dawley rat sera were administered to analbuminemic rats kept under these conditions. The duration of survival was extended by the administration of two of the fractions. Several characteristics of one of these fractions coincided with those of uric acid, and body temperature of analbuminemic and Sprague Dawley rats increased within 5 min after uric acid administration.

When female analbuminemic rats were injected with 0.8 mg uric acid every 3 h, their survival time at 5 degrees C increased from 14 h to 28 h, but uric acid had no effect on analbuminemic male rats. When female rats were oophorectomized 1 week before cold exposure, the injection of uric acid had no effect on their survival. Furthermore, uric acid did not increase the survival of the female rats that were administered a pellet containing 5 mg testosterone 1 week before the cold exposure. When the male rats were castrated 1 week before cold exposure, their survival time decreased from 20 h to 14 h, and administrations of 5 mg estradiol pellet at the time of castration and 0.8 mg uric acid every 3 h during cold exposure increased their survival time to 23 h.