Effect of Exercise-Induced Lactate Elevation on Brain Lactate Levels During Hypoglycemia in Patients With Type 1 Diabetes and Impaired Awareness of Hypoglycemia

Since altered brain lactate handling has been implicated in the development of impaired awareness of hypoglycemia (IAH) in type 1 diabetes, the capacity to transport lactate into the brain during hypoglycemia may be relevant in its pathogenesis. High-intensity interval training (HIIT) increases plasma lactate levels. We compared the effect of HIIT-induced hyperlacticacidemia on brain lactate during hypoglycemia between 1) patients with type 1 diabetes and IAH, 2) patients with type 1 diabetes and normal awareness of hypoglycemia, and 3) healthy participants without diabetes (n = 6 per group). All participants underwent a hypoglycemic (2.8 mmol/L) clamp after performing a bout of HIIT on a cycle ergometer. Before HIIT (baseline) and during hypoglycemia, brain lactate levels were determined continuously with J-difference-editing 1H-MRS, and time curves were analyzed using nonlinear mixed-effects modeling. At the beginning of hypoglycemia (after HIIT), brain lactate levels were elevated in all groups but most pronounced in patients with IAH. During hypoglycemia, brain lactate decreased ∼30% below baseline in patients with IAH but returned to baseline levels and remained there in the other two groups. Our results support the concept of enhanced lactate transport as well as increased lactate oxidation in patients with type 1 diabetes and IAH.