Insulin resistance in non-obese african hypertensive subjects with normal glucose tolerance

Abstract

Insulin resistance and the concomitant compensatory hyperinsulinaemia, independent of obesity or abnormal glucose tolerance have been demonstrated to be associated with essential hypertension in Caucasians.

This study was conducted to establish if insulin resistance and the accompanying hyperinsulinaemia is also associated with essential hypertension in Africans. A sample of 15 newly detected, untreated hypertensive non-obese subjects, together with 15 normotensive controls matched for age, sex and body mass index were studied. The modified Harano's insulin sensitivity test was employed. All subjects as well as the controls had normal oral glucose tolerance by WHO criteria. The mean systolic blood pressure in hypertensive subjects was 176±6 mmHg while the mean diastolic blood pressure was 111±2 mmHg. The controls had a mean systolic blood pressure of 131±3 mmHg and a mean diastolic blood pressure of 83±1 mmHg. The mean ages of the hypertensive subjects and controls were 38.5±!. 7 years and 38.6±1.8 years respectively.

The mean (±sem) body weight in hypertensive subjects was 67.0±11.5 kg while that in controls was 64.6±11.3 kg. The mean height was 1.6±0.1 m in both groups, and the respective body mass indices were 24. 6±0. 9 kg/m2 and 24.4±0.9 kg/m2 which were comparable (p = 0.92).

Fasting blood glucose was significantly higher (p = 0.04) by about 7% in hypertensive subject's (mean = 4.4±0.1 mmol/l), than in controls (mean = 4.1±0.1 mmol/l). Steady state blood glucose concentration (SSBG) was significantly higher (p = 0.009) by about 26% in hypertensive subjects (mean = 5.0±0.3 mmol/I) than in controls (mean = 3.7±0.3 mmol/l). The mean metabolic clearance rate in hypertensive subjects (0.007± 0.001

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iii ml/kg/min) was stg nificarrtly lower (p = 0.014 by about 28.5% than that of controls (mean = 0.009±0.001 ml/kg/min.). There was no significant correlation between body mass index and systolic blood pressure in both groups (1' = 0.1, p > 0.7 and l' = 0.3, p > 0.2 respectively). A similar insignificant correlation was observed with diastolic blood pressure in the two groups. There was a positive and significant correlation between waist: hip ratio and systolic blood pressure in hypertensive subjects (r = 0.5, p < 0.05) but not in the controls (r = 0.2 p > 0.4). No significant correlation was observed between waist: hip ratio and diastolic blood pressure in both groups (r = 0.3, p> 0.2, and r = 0.2 p > 0.4, respectively). There was a negative correlation between metabolic clearance rate and systolic blood pressure in the control group which was statistically significant (r = -0.5, p<0.05), but not in the hypertensive subjects. No significant correlation was observed between steady state blood glucose concentration and both systolic and diastolic blood pressure in the hypertensives as well as controls. There was no significant difference in the mean fasting plasma insulin concentrations between the two

groups. There was no

correlation between fasting plasma insulin

concentration and blood pressure in both g rou pa.). These data indicate that there is an abnormality of insulin -mediated glucose metabolism in African hypertensives, suggesting an association between insulin resistance and essential hypertension.