Effect of a physiological insulin infusion on the cardiovascular responses to a high fat meal: evidence supporting a role for insulin in modulating postprandial cardiovascular homoeostasis in man.

1. While the haemodynamic adjustments occurring after meal ingestion and the different effects of meals of different composition on these changes are well established, the mechanisms underlying these changes are less clear. Insulin, which has been shown to be both a positive inotrope and to stimulate vasodilatation in the skeletal muscle vascular bed, may account for the different cardiac and regional haemodynamic responses to high fat and high carbohydrate meals. 2. This study assessed the effect of an insulin infusion reproducing the plasma insulin profile seen after a high carbohydrate meal on the cardiovascular and regional haemodynamic response to a high fat meal. All measurements were carried out non-invasively in nine healthy lean subjects (mean age 24.5 +/- 1.3 years). 3. The high fat meal resulted in increases in cardiac output (0.7 +/- 0.32 l/min, P < 0.001), heart rate (7.8 +/- 2.1 beats/min, P < 0.001) and insulin (25.1 +/- 4.2 m-units/l, P < 0.001), and a decline in systemic vascular resistance (-1.9 +/- 0.9 units, P < 0.05) and superior mesenteric artery vascular resistance (-45 +/- 9 units, P < 0.01). After the high fat meal alone, calf vascular resistance and blood pressure did not change. After the high fat meal accompanied by insulin (peak insulin 86.1 +/- 10.1 m-units/l) there were greater cardiac responses [(P < 0.001); cardiac output, 1.17 +/- 0.36 l/min, and heart rate, 13.4 +/- 2.1 beats/min], and a larger fall in systemic vascular resistance and superior mesenteric artery vascular resistance. Unlike the high fat meal alone, the high fat meal with insulin was accompanied by a fall in calf vascular resistance (8.3 +/- 3.3 units) and blood pressure (3.8 +/- 1.6 mmHg). 4. The results of this study support a role for insulin in modulating postprandial cardiovascular homoeostasis; in particular, by its depressor action on skeletal muscle vasculature, insulin may in part contribute to the fall in blood pressure seen in the elderly, who have an inadequate cardiac response to the fall in systemic vascular resistance occurring after meal ingestion.