At 08:00 hours in the morning at day 2, insulin infusion will be increased to 1.5 mU/kg/min for each subject and the PG will be kept at a plateau of 5.5 mmol/L by a controlled variable intravenous infusion of glucose (10% glucose enriched with 4mg [6,6-2H2] glucose /ml) for one hour. Afterwards, PG is allowed to fall to a plateau of 3.5 mmol/L, then to a nadir of 2.5 mmol/L, then to a blood glucose of 4.0 mmol/L and finally back to a level of 5.5 mmol/L for safety reasons. Blood sampling for measurement of [6,6-2H2] glucose, glucagon, insulin, counterregulatory hormones, lactate, free fatty acids, glycerol, vital signs, hypoglycaemic symptoms questionnaire and hypoglycaemic awareness will be performed at each PG plateau.