Suppression of post-glucose hyperinsulinaemia does not affect blood pressure in either normotensive or hypertensive...

1. Hyperinsulinaemia and insulin resistance are thought to be intimately involved in the development of hypertension, but controversy remains as to whether hyperinsulinaemia is a consequence or a cause of hypertension per se, and whether it plays a role in the short-term regulation of blood pressure. 2. We studied six hypertensive patients [blood pressure 161(9)/101(2) mmHg] and seven normotensive control subjects [blood pressure 122(6)/76(4) mmHg], (P < 0.005) using two oral glucose tolerance tests of 3 h duration. In one of these tests the endogenous insulin response was inhibited with subcutaneous octreotide. 3. After placebo, hypertensive patients had slightly but significantly higher blood glucose levels than controls (P < 0.0001), but comparable insulin concentrations (P > 0.5). Plasma noradrenaline levels were consistently lower in the hypertensive group (P < 0.001). Blood pressure did not change in either group during the 3 h after glucose ingestion. 4. Octreotide completely abolished the immediate insulin response to glucose in all subjects (both P < 0.0001) and caused a delayed and significantly increased glycaemic response in both groups (P < 0.0001). There were no significant differences in plasma glucose responses between groups: however, after octreotide, the hypertensive subjects had a greater insulin suppression than the controls (P < 0.02). Octreotide suppressed noradrenaline levels in the normotensive group (P < 0.001); they were also suppressed in the hypertensive group, but just failed to reach significance (P = 0.056). Throughout the study the hypertensive group's noradrenaline levels remained generally lower than those in the control group (P < 0.0001). 5. In this study there were no differences between hypertensive and normotensive subjects in fasting or post-glucose insulin levels, nor any significant change in blood pressure in either group when post-glucose hyperinsulinaemia was suppressed. This argues against insulin playing a direct role in the short-term regulation of blood pressure.