Effect of the Gut Hormone Gastric Inhibitory Polypeptide (GIP) on Skeletal Muscle Blood Flow

This study is a cross-over trial comparing the effect of gastric inhibitory polypeptide (GIP) versus saline on skeletal muscle blood flow. Each participant will receive both treatments (intravenous infusions) in the following order: Infusions: 1) GIP - infused intravenously at 2 pmol/kg/min for 120 mins to raise plasma GIP levels. 2) Saline - infused intravenously for 120 mins. A total of 13 healthy individuals with no history of cardiometabolic disease will be required to complete the study. Participants will be invited to attend an initial screening/familiarisation session, followed by 2 clinical testing sessions between 1 and 4 weeks apart. Participants will receive the GIP infusion first and then crossed-over to the saline infusion on the second clinical testing visit. In addition to GIP and saline infusion, all participants will also undergo a variable rate intravenous glucose tolerance test to mimic blood glucose excursions similar to an oral glucose tolerance test. The following measurements will be conducted: Clinical chemistries and anthropometrics: Fasting clinical chemistries (glucose, insulin, lipid profile, HbA1c) and body composition (height, weight) will be measured. Clinical chemistries will be assessed via an accredited pathology laboratory. Microvascular blood flow responses in skeletal muscle: Microvascular blood flow will be measured via contrast-enhanced ultrasound imaging of the thigh muscle at baseline (0 min) and at 60 min and 120 min post-GIP and -saline infusion. Femoral artery blood flow responses: Femoral artery blood flow will be measured via 2D and Doppler ultrasound imaging at baseline (0 min) and at 60 min and 120 min post-GIP and -saline infusion. Metabolic and hormonal responses: Blood glucose, plasma insulin and plasma GIP levels will be measured at regular time points over 120 mins during the infusion of GIP and saline.