Insulin acts in certain regions of the human brain. If the hormone is administered via an intranasal spray, the insulin is delivered to the brain directly. In lean people, the administration of intranasal insulin results in an improvement of insulin action in the whole body by suppressing endogenous glucose production, causing more glucose to be absorbed by the tissue. In overweight subjects these effects did not occur. These were the results of a study by DZD scientists from Tübingen and Düsseldorf, which was published in the journal Diabetes.
In order to measure the endogenous glucose production and the glucose uptake of the tissue, the 21 study participants underwent two hyperinsulinemic-euglycemic clamps with labeled glucose infusion (method for determining insulin sensitivity). In addition, the participants were administered an intranasal insulin spray or a placebo spray. The researchers investigated brain activity by means of functional magnetic resonance tomography (fMRI).
After the insulin administration, the endogenous glucose production decreased and glucose uptake in the tissue increased in the lean subjects. In addition, the researchers also observed increased activity in the hypothalamus and striatum (part of the basal ganglia, which belong to the cerebrum). No such effects were detected in the overweight participants. This could be due to insulin resistance in the brain of overweight people, which has been known for some time. This insulin resistance of the brain consequently has negative effects on the metabolism in the body, the researchers suspect.
The study was conducted by the Institute for Diabetes Research and Metabolic Diseases of Helmholtz Zentrum München at the University of Tübingen and the German Diabetes Center in Düsseldorf, both partners of the German Center for Diabetes Research (DZD).
Martin Heni, Robert Wagner, Stephanie Kullmann, Sofiya Gancheva, Michael Roden, Andreas Peter, Norbert Stefan, Hubert Preissl, Hans Ulrich Haring, Andreas Fritsche. Hypothalamic and striatal insulin action suppresses endogenous glucose production and may stimulate glucose uptake during hyperinsulinemia in lean but not in overweight men. Diabetes, 2017; db161380. https://doi.org/10.2337/db16-1380