HYPERINSULINEMIA IN HYPERTENSION - INCREASED SECRETION, REDUCED CLEARANCE OR BOTH

Peripheral hyperinsulinism is said to be associated and perhaps implicated in the pathogenesis of hypertension. There is however some inconsistency in the evidence of the relationship between insulin and blood pressure. We prospectively investigated glucose metabolism, insulin and C-peptide values and serum lipids in a large sample of hypertensive as compared with age and body habitus-matched normotensive subjects. As a group, the 145 hypertensives (blood pressure: 160/99+/-8.5/6.5 mmHg, mean+/-SD) had significantly elevated fasting plasma insulin (p<0.02), total and LDL-cholesterol (p<0.01) than 132 normotensive control subjects. The fasting HbA1c (glycated hemoglobin Alc)/insulin ratio, an estimate of insulin sensitivity, was significantly lower (5.15+/-1.45) in the hypertensives than normotensives (5.8+/-1.5, p<0.001). Hypertensives had normal fasting C-peptide levels and lower C-peptide/insulin molar ratios, indicating low hepatic insulin extraction. There was no correlation between mean blood pressure (1/3 systolic+2/3 diastolic) and fasting serum C-peptide (p=0.14), insulin (p=0.11), HbA1c/insulin ratio (p=0.6), C-peptide/insulin ratio (p=0.22) and HbA1c (p=0.19), even after adjusting for age, BMI and family history of diabetes. The differences between hypertensives and normotensives persisted after dividing the subjects according to the presence/absence of either obesity or impaired glucose tolerance, but the significance was lost due to the smaller samples of the subgroups. The obese hypertensives with impaired glucose tolerance had the lowest values of insulin sensitivity and clearance in the fasting state. These findings suggest that in our hypertensives fasting hyperinsulinism is dependent more on reduced hepatic clearance than hypersecretion: plasma insulin and C-peptide concentration is not related to blood pressure.