Effects of Calcium on Gut Functions and Blood Glucose in Humans With Type 2 Diabetes

Each participant will be required to consume a standardised dinner meal (beef lasagne; total energy content: 602 kcal; McCain Food, Wendouree, Victoria, Australia) on the night before each visit by 7 pm. After fasting overnight for \~ 13.5 hours and refraining from exercise and alcohol during the previous 24 hours, the participant will arrive in the laboratory at 8.30 am. After confirming adherence to the study requirements, vital signs ( blood pressure, heart rate and body temperature) will be measured to establish baseline values for safety, and they will be monitored throughout the study. Then, a manometric catheter will be inserted through an anaesthetised nostril and allowed to pass through the stomach and into the duodenum by peristalsis. The infusion port will be positioned \~ 14 cm distal to the pylorus. The correct positioning of the catheter will be monitored continuously by measurement of the transmucosal potential difference in the stomach (\~ -40 mV) and the duodenum (\~ 0 mV). Once the catheter has been positioned correctly, an intravenous cannula will be placed into a forearm vein for regular blood sampling. At time = -30 minute, a baseline blood sample (7 ml), visual analogue scale (VAS) questionnaire to assess gastrointestinal (GI) symptoms, and breath sample to assess gastric emptying will be collected. Then the infusion of one of the study treatments, i.e. i) saline, ii) 500 mg CaCl2 or iii) 1000 mg CaCl2), will commence and continue for 75 minutes (times = -30 to 45 minutes). At time = -1 minute, participants will consume, within 1 minute, a mixed-nutrient drink (350 mL, containing 500 kcal, 74 g carbohydrates) labelled with 100 mg 13C-acetate for measurement of gastric emptying by non-invasive breath sampling at regular intervals, for subsequent analysis of 13CO2 levels. Blood samples for the measurement of plasma glucose and hormone concentrations, and VAS questionnaires, will be collected before and after the mixed-nutrient drink. At time = 240 minute, after collecting final blood and breath samples and VAS questionnaire, the intravenous cannula will be removed and the participant will be served a light lunch, after which they will be allowed to leave the laboratory. A total of 98 mL of blood (14 sampling time points, 7 mL each) will be taken on each study day (study total of 310 mL, including screening and glucose tolerance test samples).