Blood sugar levels and adrenal weights (where possible) were recorded, after a 24-h fast, in normal intact, adrenal-demedullated, and adrenalectomized rats kept at 4 °C for up to 130 days. These were compared with data from control rats kept at 21 °C. Hypoglycemia (relative to the control value) prevailed in both normal intact and, more profoundly, in adrenal-demedullated rats during the first 24 h of chilling but no deaths occurred. Adrenalectomized rats, whose blood sugar level at 21 °C was subnormal, at 4 °C soon showed extreme hypoglycemia and died. More prolonged chilling in normal intact rats resulted in hyperglycemia which lasted until after the 25th day. In contrast, in chilled adrenal-demedullated animals the blood sugar remained at the control level throughout this period. At the 50th day the blood sugar of normal intact animals fell to the control value and remained so thereafter. A similar fall in adrenal-demedullated rats resulted in hypoglycemia, but a rise to control values was recorded from the 75th day. Adrenocortical hypertrophy was generally more extensive in the demedullated animals than in the normal intact animals but was absent in both groups by the 130th day. We conclude that the adrenal medulla, besides helping to provide extra blood glucose during exposure to short-term chilling, is also responsible for the sustained hyperglycemia of rats chilled for prolonged periods and thus assists in their acclimation to long-term cold stress.
Dynamic modelling of cold-hardiness in tea buds by imitating past temperature memory
