INS and diabetes mellitus: To explore the physiological significance of succinate as an insulin secretagogue, we investigated the potential link between circulating succinate kinetics and pancreatic β cell function in response to an OGTT and to an isoglycemic intravenous glucose infusion (IIGI) in a cohort of individuals with normal glucose tolerance (NGT) or individuals without NGT according to the American Diabetes Association criteria (60) (Figure 6A; clinical and anthropometric data in Table 1).