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 HOMEOSTASIS IN MAN

1. While the haemodynamic adjustments occurring after meal ingestion a nd the different effects of meals of different composition on these ch anges are well established, the mechanisms underlying these changes ar e less clear. Insulin, which has been shown to be both a positive inot rope and to stimulate vasodilatation in the skeletal muscle vascular b ed, may account for the different cardiac and regional haemodynamic re sponses to high fat and high carbohydrate meals.2. This study assessed the effect of an insulin infusion reproducing the plasma insulin prof ile seen after a high carbohydrate meal on the cardiovascular and regi onal haemodynamic response to a high fat meal. All measurements were c arried 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/m in, P<0.001) and insulin (25.1 +/- 4.2 m-units/l, P< 0.001), and a dec line in systemic vascular resistance (-1.9 +/- 0.9 units, P<0.05) and superior mesenteric artery vascular resistance (-45 +/- 9 units, P<0.0 1). After the high fat meal alone, calf vascular resistance and blood pressure did not change. After the high fat meal accompanied by insuli n (peak insulin 86.1 +/- 10.1 m-units/l) there were greater cardiac re sponses [(P<0.001); cardiac output, 1.17 +/- 0.36 l/min, and heart rat e, 13.4 +/- 2.1 beats/min], and a larger fall in systemic vascular res istance and superior mesenteric artery vascular resistance. Unlike the high fat meal alone, the high fat meal with insulin was accompanied b y a fall in calf vascular resistance (8.3 +/- 3.3 units) and blood pre ssure (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, i nsulin may in part contribute to the fall in blood pressure seen in th e elderly, who have an inadequate cardiac response to the fall in syst emic vascular resistance occurring after meal ingestion.