Tracer determined rates of glucose production and uptake will be calculated using the equations for non-steady state. The volume of distribution of glucose will be assumed to be 200 ml/kg and a pool correction factor of 0.65 will be used in the calculations. Glucose specific activity will be calculated as the ratio between the tracer contraction and the prevailing plasma glucose concentration. The Hot Ginf technique will be used to maintain constant specific activities throughout the studies.