The Effect of Glucagon on Cerebral Glucose Metabolism in Healthy Humans

This is a pilot study in which the investigators will investigate the effect of exogenous glucagon on cerebral glucose metabolism in healthy humans. Participants will participate in either part C or part D of the study, and each participant will participate in three study days. During a study day the participant will receive an intravenous infusion of either glucagon, glucose (in an adjustable rate to match to glucose concentrations achieved with the glucagon infusion) or saline. During each study day an 18F-flouro-deoxy-glucose (FDG) Positron Emission Tomography (PET)/Computed Tomography (CT) scan will be performed to quantify cerebral glucose metabolism during the first part (acute effect) of the glucagon/glucose/saline infusion (part C) or the last part (later effect) of the glucagon/glucose/saline infusion (part D).