OBJECTIVE The aim of this study was to elucidate whether age plays a role in the expansion or regeneration of beta-cell mass. RESEARCH DESIGN AND METHODS We analyzed the capacity of beta-cell expansion in 1.5- and 8-month-old mice in response to a high-fat diet, after short-term treatment with the glucagon-like peptide 1 (GLP-1) analog exendin-4, or after streptozotocin (STZ) administration. ...