1. The present experiments were designed to elucidate the reasons for the fall in central body temperature during hypoglycaemia.
2. The first experiment was carried out at a room temperature of 25 °C on 11 male subjects. Hypoglycaemia was induced by infusion of insulin. Heat production (calculated from respiratory gas exchange) rose from a baseline of 5.10 ± 0.13 kJ/min (mean ± sem) to a peak of 6.25 ± 0.21 kJ/min (P < 0.001), but core temperature fell concurrently by 0.51 ± 0.08°C and skin temperature fell by 1.1 ± 0.2°C. The net heat loss was due to peripheral vasodilatation and sweating.
3. To determine the effect of insulin-induced hypoglycaemia on thermoregulation in a cool environment, the experiment was repeated at a room temperature of 18–19°C on five of the subjects who had air blown over them until shivering was sustained. During this time heat production rose to 10.13 ± 1.67 kJ/min, but core temperature remained constant. Shivering stopped as plasma glucose fell below 2.5 mmol/l during insulin infusion and the subjects said they no longer felt cold.
4. During hypoglycaemia in the cold peripheral vasodilatation and sweating occurred, skin temperature fell by up to 0.8°C and core temperature fell below 35°C, so subjects had to be rewarmed.
5. Recovery of plasma glucose after hypoglycaemia in the cold was impaired at low body temperatures, but shivering was restored within seconds when glucose was given intravenously.