Effects of intraduodenal glucose concentration on blood pressure and heart rate in healthy older subjects

The aims of this study were to determine whether the hypotensive and heart rate responses to small intestinal glucose infusion are dependent on the glucose concentration. Eight healthy subjects, aged 65–78 years, were studied on 3 separate days in random order. Each subject received intraduodenal infusions of 50 g of glucose in either 300 mL (16.7%), 600 mL (8.3%), or 1200 mL (4.1%) of saline (0.9%) at a rate of 3 kcal/min for 60 minutes (t = 0–60 minutes), followed by saline (0.9%) for a further 60 minutes (t = 60–120 minutes). During the infusions, blood pressure (systolic and diastolic) and heart rate were measured every 3 minutes, and blood glucose concentrations every 15 minutes. Systolic and diastolic blood pressure fell (P < .0001), and heart rate and blood glucose increased (P = .0001 for both) over time, during all 3 infusions. Between t = −2–120 minutes, there was no difference in systolic blood pressure (P = .20), diastolic blood pressure (P = .61), or heart rate (P = .09) over the study days. There was also no significant difference in the glycemic response to the infusions. We conclude that in healthy older subjects, glucose concentration does not affect the blood pressure or heart rate responses to intraduodenal glucose and that, therefore, the magnitude of the postprandial fall in blood pressure induced by oral glucose is likely to depend primarily on the small intestinal glucose load.