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BACKGROUND: Oxygen free radicals may play roles in hypertension both in arteriolar constriction and in formation of lesions. OBJECTIVE: To quantify free radical production in blood plasma of genetic hypertensives. DESIGN: Hydrogen peroxide levels were measured, because it is one of the most stable reactive oxygen species. METHODS: An electrode technique was used to determine plasma hydrogen peroxide levels after blockade of endogenous catalase with sodium azide. This method was validated by an independent spectrophotometric technique. RESULTS: Members of the essential hypertensive group (n=21) had higher plasma hydrogen peroxide levels (3.16+/-0.14 versus 2.50+/-0.16 micromol/l, P=0.005) than did members of the normotensive group (n=29). Furthermore, within the normotensive group, those with a family history of hypertension (n=15) exhibited higher hydrogen peroxide levels (2.83+/-0.27 versus 2.14< or =0.13 micromol/l, P=0.03) than did those without such a family history (n=14). Plasma hydrogen peroxide levels in these 50 subjects were correlated to their mean arterial pressures (r=0.54, P < 0.001). When hypertensives were grouped with normotensives without a family history of hypertension, the correlation improved (r=0.70, P< 0.001). Statistical analysis (two-way analysis of variance) revealed that a family history of hypertension was a better predictor of plasma hydrogen peroxide production than was blood pressure status (P=0.003 versus P=0.093). Further investigations showed that superoxide is produced in plasma and that one of its sources is xanthine oxidase. CONCLUSIONS: Hydrogen peroxide is produced in blood plasma and elevation of its level could constitute a pathogenic factor in vascular organ damage attendant upon systemic hypertension.
Lacy et al. (Sun,) studied this question.