1. Department of Medicine III and Center for Healthy Aging, Technische Universität Dresden, D-01307 Dresden, Germany
2. Department of Endocrinology, University of Duisburg-Essen, University Hospital Essen, D-45147 Essen, Germany
3. Institute of Physiology, University of Zurich, CH-8057 Zurich, Switzerland
4. Molecular Endocrinology Laboratory, Department of Metabolism, Digestion and Reproduction, Imperial College London, London SW7 2AZ, UK