Effects of calcium on gut functions and blood glucose in healthy humans

The intervention in this study consists of a 75-min intraduodenal infusion of an isotonic solution containing either calcium chloride (CaCl2) or control (saline). Participants enrolled into the study will receive, in randomised, double-blind fashion (i) Saline (control), (ii) 500 mg CaCl2, (iii) 1000 mg CaCl2, each occurring on separate sessions. Each study session will be 4-6 hours in duration and will be separated by at least 4 (and up to 10) days. Studies will be carried out in the Clinical Research Facility of the Adelaide Medical School, the University of Adelaide, by staff and students trained in the required techniques. To ensure adherence to the intervention, research staff will closely supervise the participants throughout the study visit. Participants will be required to consume a standardised dinner meal (beef lasagne; total energy content: 602_kcal; McCain Food, Wendouree, Victoria, Australia) the night before each visit by no later than 7 pm. After fasting for ~ 13.5 hours overnight and refraining from exercise and alcohol during the previous 24 hours, participants will arrive at the laboratory at 8.30 am. Upon arrival and after confirming adherence to the study requirements, their vital signs, including 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 17-channel 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 t = -30 min, a baseline blood sample (7 ml), visual analogue scale (VAS) questionnaire to assess GI symptoms and breath sample to assess gastric emptying will be collected. Then 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 (t = -30 to t = 45). At t = -1 min, participants will consume, within 1 min, a mixed-nutrient drink (Nestle, 500 kcal, 350 ml) labelled with 150 mg of 13C-acetate for measurement of gastric emptying by non-invasive breath sampling at regular intervals, for subsequent analysis of 13CO2. Blood samples for the measurement of plasma hormone concentrations and glucose, and VAS scores, will be collected before and after the mixed-nutrient drink. At t = 240 min, after collecting final blood and breath samples and VAS scores, the i.v. cannula will be removed and participants 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 302 mL).