Insulin resistance is a central pathophysiological component of type 2 diabetes and is associated with a high risk of cardiovascular disease. The tissue in which it manifests are mainly muscle, liver, and adipose tissue. Since the transport of glucose to the brain is independent of insulin, this organ has traditionally not been studied in this regard. In animal experiments, however, knockout of the insulin receptor in the brain leads to obesity and peripheral insulin resistance. This finding of insulin action in the brain could also be confirmed in human studies.

The investigators intend to investigate whether central nervous insulin action affects insulin secretion in humans. For this purpose, nasal insulin and placebo are administered 15 minutes before a hyperglycemic hyperinsulinemic clamps, which stimulate insulin secretion. Insulin sensitivity of the brain is measured by a an established protocol with functional magnetic resonance imaging before and after nasal insulin administration.

Inclusion Criteria:

• HbA1c ≤6.0%
• normal glucose tolerance during 75g oral glucose tolerance test (OGTT)

Exclusion Criteria:

• Not removable metal parts in or on the body
• manifest cardiovascular disease
• claustrophobia
• recent surgery (less than 3 months)
• Simultaneous participation in other studies
• Acute disease or infection within the last 4 weeks
• neurological and psychiatric disorders
• treatment with centrally acting drugs
• hemoglobin Hb <13g / dl
• Hypersensitivity to any of the substances used