Mechanisms mediating postprandial blood pressure reduction in young and elderly subjects

The objective of this study was to clarify potential differences in hormonal, neurogenic and hemodynamic mechanisms mediating postprandial blood pressure (BP) reduction. In 12 age- and body mass index-matched young normotensive (NT) subjects, 21 elderly NT, 17 young hypertensive (EH) patients, and 32 elderly EH, we measured BP, blood glucose, plasma insulin (IRI), and norepinephrine (NE) levels before and every 30 min for 3 h after a 75 g oral glucose solution ingestion. Cardiac output (CO) and total systemic resistance (TSR) were also measured before and 1 h after oral glucose ingestion. Postprandial BP reduction, defined as 10% or more decline in mean BP was recognized in 3/12 (25%) young NT, 9/21 (43%) elderly NT, 5/17 (29%) young EH, and 20/32 (63%) elderly EH. The most consistent finding was that the IRI response to glucose was high in all subjects with postprandial BP reduction regardless of age or level of BP, although changes in blood glucose levels showed no major differences. The NE level was low in young and elderly NT with postprandial BP reduction, but in EH the level was not different. Increases in CO in elderly subjects with postprandial BP reduction was significantly less than that in subjects without postprandial BP reduction. In addition, the decrease in TSR in young subjects with postprandial BP reduction was significantly greater than that in subjects without postprandial BP reduction, while the decrease in elderly subjects was not different between the subjects with and without postprandial BP reduction. In conclusion, postprandial BP reduction in elderly EH appears to be associated with hyperinsulinemia independent of age and BP status. The vasodilator effects of insulin may contribute to postprandial BP reduction. A second conclusion is that impairment of sympathetic nervous system responses to insulin may also contribute to altered postprandial hemodynamic responses especially in EH, suggesting multiple mechanisms in origin of postprandial BP reduction.