GIP contributes to postprandial regulation of splanchnic blood supply in humans with type 2 diabetes: a randomised, single-blinded, placebo-controlled, crossover study.
AIMS/HYPOTHESIS: In healthy lean humans, endogenous glucose-dependent insulinotropic polypeptide (GIP) contributes significantly to the postprandial increase in arteria mesenterica superior blood flow. The vascular biology related to activation of the GIP receptor is markedly impaired in individuals with type 2 diabetes and is sometimes absent. In this population, we investigated the role of endogenous GIP on postprandial splanchnic blood flow by using the GIP receptor antagonist, GIP(3-30)NH2. The primary outcome of this study was the changes in blood flow in arteria mesenterica superior during oral glucose with or without GIP receptor antagonist infusion. METHODS: Ten participants with type 2 diabetes (age 20-80 years, BMI 20-35 kg/m2, and HbA1c >48 mmol/mol and <75 mmol/mol) were investigated in a randomised, placebo-controlled, crossover study. On four separate occasions, participants received the following treatment: oral glucose + i.v. GIP(3-30)NH2; oral glucose + i.v. saline (154 mmol/l NaCl); oral water + i.v. GIP(3-30)NH2; oral water + i.v. saline. Participants were randomly assigned to intervention groups using (random.org). Participants were unaware of allocation, while investigators were aware. No additional allocation concealment procedures were used. During all four interventions, splanchnic blood flow was measured using phase-contrast MRI in the arteria mesenterica superior, truncus coeliacus and vena portae during oral glucose (75 g) or water ingestion. The study was conducted at Rigshospitalet, Copenhagen. Liver volume and oxygenation, as well as gallbladder volume, were assessed. Blood samples were collected and analysed for insulin, C-peptide, GIP, glucagon and glucose. RESULTS: Oral glucose alone increased mean blood flow in arteria mesenterica superior by 57% (95% CI 26, 88) and this was 15% (95% CI -2, 32) lower during concomitant GIP receptor antagonist infusion, p=0.012. Infusion of GIP receptor antagonist during oral glucose treatment did also result in lower insulin secretion, C-peptide and C-peptide/glucose ratio compared with saline infusion, whereas glucagon levels and plasma glucose were unaffected. Oral water did not affect any outcomes. CONCLUSIONS/INTERPRETATION: Endogenous GIP contributes to postprandially increased splanchnic blood flow in people with type 2 diabetes. TRIAL REGISTRATION: ClinicalTrials.gov NCT06426823 FUNDING: This work was supported by the Novo Nordisk Foundation.