1. Section on Integrative Physiology and Metabolism, Joslin Diabetes Center and Harvard Medical School, Boston, MA 02215, USA.
2. Institute for Diabetes and Obesity, Helmholtz Zentrum München, 85764 Neuherberg, Germany.
3. Department of Clinical Science, University of Bergen, 5020 Bergen, Norway.
4. Hormone Laboratory, Haukeland University Hospital, 5020 Bergen, Norway.