Effects of intraduodenal glucose, fat, and protein on blood pressure, heart rate, and splanchnic blood flow in healthy older subjects.

BACKGROUND Postprandial hypotension frequently occurs in the elderly. The hypotensive response to a meal is triggered by the interaction of nutrients with the small intestine; information relating to the effects of different macronutrients on blood pressure (BP) is limited and inconsistent. OBJECTIVE The objective of the study was to determine the effects of intraduodenal glucose, fat, and protein on BP, heart rate (HR), and superior mesenteric artery (SMA) blood flow in healthy older subjects. DESIGN Eight subjects received intraduodenal glucose (64 g), fat (10% oil emulsion), protein (72 g whey), or saline (0.9%) at a rate of 2.7 mL/min for 90 min, followed by intraduodenal saline for 30 min. BP, HR, and SMA blood flow were measured. RESULTS The falls in systolic BP during infusions of glucose, fat, and protein did not differ significantly (P=0.97); however, the fall occurred significantly earlier during the glucose infusion; (18+/-3.0 min) than during the fat (46+/-11.0 min; P=0.02) and protein 33+/-7 min; P=0.04) infusions. The increases in HR during glucose, fat, and protein infusions (P<0.0001 for all) did not differ significantly. SMA blood flow increased significantly after all infusions (P<0.001 for all), but the increase was significantly (P<0.05) lower after protein than after the other infusions. CONCLUSIONS Intraduodenal glucose, fat, and protein decrease systolic BP in healthy older subjects, but the onset of the hypotensive response is earlier after glucose, and the effect of protein on SMA blood flow is less than that of the other nutrients.