3. Acute insulin response to intravenous glucose (unvalidated measure of acute insulin response to intravenous glucose AIRglucose). Next a high-speed (900 ml/hr) 20% glucose infusion over 10-25 minutes will be commenced (total volume infused up to 410 ml). Samples will be collected at -5, -2 min (before starting the high speed infusion) and then at 2 minute intervals for 10 minutes following the start of the glucose infusion.