***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Several lines of evidence suggest that patients with essential hypertension have impaired endothelial nitric oxide activity and increased superoxide anion production . However , the mechanisms underlying these abnormalities remain unknown . We measured  enzymatic superoxide dismutase ( SOD ) and glutathione peroxidase ( GPX ) activities  in erythrocytes and whole blood , respectively , in 30 newly-diagnosed , normolipidaemic untreated mild hypertensive patients and in 164 age-matched healthy controls .  SOD and GPX activities in hypertensive patients ( 806 ± 225 U/Hb.g and 5491 ± 2073 U/L , respectively ) were significantly lower than in the control group ( 931 ± 202 U/Hb.g and 6669 ± 1560 U/L , respectively ) ( P < 0.005 ) . no significant association was found between these antioxidant enzyme activities and blood pressure in normotensive controls . in the hypertensives , only log-transformed sod activity showed a significant negative correlation with systolic and diastolic blood pressure ( r = 0.37 , P < 0.05 ; r = 0.64 , P < 0.0001 , respectively ) . the low endogenous antioxidant enzyme activities observed may in turn result in decreased superoxide anion removal leading to nitric oxide inactivation 
    Output:
    
This meta- analysis suggests that the GSTM1 and GSTT1 null polymorphisms are not associated with the risk of hypertension .