Dapagliflozin is a highly selective, reversible and potent inhibitor of the sodium-glucose-linked Transporter 2 (SGLT2), which was successfully investigated for its use as a treatment option in type 2 diabetes mellitus. The effect of dapagliflozin is an increased glucosuria, and it was shown that mean blood glucose concentrations and postprandial glucose excursion in special were significantly reduced in type 2 diabetic patients. Due to its mechanism-of action it seems likely that also type 1 diabetic patients will benefit from dapagliflozin. The present study is focused on the effects of dapagliflozin on fasting glucose homeostasis and postprandial glucose excursion in male type 1diabetic patients. Participants will subsequently receive 10 milligrams of dapagliflozin and placebo for 3 days (equals 2 x 30mg per cross-over period) in a double-blind, randomised, cross-over design. The effects will be measured via euglycemic hyperinsulinemic clamp studies (fasting glucose homeostasis) and euglycemic oral glucose tolerance clamp tests (postprandial glucose excursions).

Inclusion Criteria:

• Type 1 diabetes mellitus (duration of disease at least 5 years)
• C-peptide concentration < 0.2µg/l
• male sex
• aged 18 to 60 years
• Body Mass Index 20 - 25 kg/m2
• no measurable, clinically relevant ketonuria

Exclusion Criteria:

• insufficient venous status on both forearms
• renal and/or hepatic insufficiency (including microalbuminuria and/or albumin/creatinin-ratio)
• history of cancer
• intake of medication and/or substances capable to influence insulin sensitivity within the last 3 months prior to study inclusion
• alcohol- and/or drug abuse, nicotine consumption > 5 cigarettes / 24h
• brittle-diabetes
• history of severe hypoglycemia, defined as the need for foreign assistance independent of actual blood glucose concentration measured
• history or evidence of any other clinically significant disorder, condition or disease other than those outlined above that, in the opinion of the investigator may compromise the ability of the participant to give written informed consent, would pose a risk to subject safety, or interfere with the study evaluation, procedures or completion.