Hypothermia is a well-known concomitant of hypoglycemia in mammals. We tested the hypothesis that this hypothermia is an important adaptive response to hypoglycemia in 11 normal Sprague-Dawley rats. Twelve-hour fasted, conscious animals received primed, continuous insulin infusions for up to 8 hours. Plasma glucose was clamped between 30 and 40 mg/dL and core body temperature was monitored continuously during the insulin infusions. Five of the animals were maintained in a room temperature environment (22 to 24 degrees C) during the hypoglycemia; all became hypothermic (mean +/- SE nadir core temperature, 31 +/- 0.5 degrees C). Spontaneous activity was reduced in these animals, but they remained conscious and responsive to external stimuli. All five returned to normal behavior after euglycemia was restored at the end of the insulin infusions. In the remaining six animals, hypothermia was prevented during hypoglycemia by warming of the air in their cages (mean of hourly core temperatures, 37 +/- 0.1 degrees C). None of these animals survived more than 7 hours. The severity of the hypoglycemia was no greater in the euthermic than in the hypothermic group, as judged by the mean of individual nadir plasma glucose levels (25 +/- 1 v 24 +/- 1 mg/dl, respectively) and by the mean number of glucose values per animal that were less than 30 mg/dL (2 +/- 1 v 7 +/- 1). Plasma osmolality did not change significantly in either group during the period of hypoglycemia, suggesting that dehydration was not the cause of death in the euthermic animals.(ABSTRACT TRUNCATED AT 250 WORDS)