Oxidative stress and hyperinsulinaemia in essential hypertension: different facets of increased risk.

OBJECTIVE: To evaluate oxidative stress markers in normo- and hyperinsulinaemic essential hypertension patients, and to relate these parameters to plasma glucose and insulin levels.
METHODS: Diene conjugates, thiobarbituric acid reactive substances, iron-stimulated thiobarbituric acid reactive substances and anti-oxidative capacity of serum were detected in 32 untreated essential hypertension patients with normal glucose tolerance, divided into hyperinsulinaemic (n = 12, fasting plasma insulin level > 13.5 mU/l, means 2 SD of controls) and normo-insulinaemic (n = 20) subgroups, compared with 26 age- and body mass index-matched controls. Plasma glucose and insulin levels were measured during an oral glucose tolerance test.
RESULTS: Levels of lipid peroxidation products (diene conjugates, thiobarbituric acid reactive substances and iron-stimulated thiobarbituric acid reactive substances) were elevated and serum anti-oxidative capacity decreased both in hyper- and in normo-insulinaemic patients compared with those in controls, with no significant differences between the hypertensive subgroups. No independent correlations were detected between oxidative stress markers and fasting or stimulated plasma insulin and glucose levels. The essential hypertension patients were characterized by a lower fasting glucose: insulin ratio and enhanced plasma insulin response to oral glucose test compared with controls.
CONCLUSIONS: The results suggest that oxidative stress occurs, in addition to disturbances in glucose metabolism, in essential hypertension patients, thus potentially exposing them to increased risk of developing complications. Factors other than plasma insulin level are likely to contribute to oxidative stress in hypertensive patients with normal glucose tolerance.