Enhanced production of oxygen free radicals may play a role in hyperte
nsion by affecting vascular smooth muscle contraction, resistance to b
lood flow, and organ damage. The aim of this study was to determine wh
ether oxygen free radicals are involved in the development of salt-ind
uced hypertension. Dahl salt-sensitive (Dahl-S) and salt-resistant (Da
hl-R) rats were fed either a high salt (6.0% NaCl) or low salt (0.3% N
aCl) diet for 4 weeks. The high salt diet caused the development of se
vere hypertension in Dahl-S animals and had no effect on blood pressur
e in Dahl-R animals. A tetranitroblue tetrazolium dye was used to dete
ct superoxide radicals in microvessels of the mesentery. Light absorpt
ion measurements revealed enhanced staining along the endothelium of a
rterioles and venules in hypertensive Dahl-S animals, with significant
ly lower values in normotensive animals. in addition, a Clark electroc
hemical electrode was used to measure hydrogen peroxide levels in fres
h plasma. Hypertensive Dahl-S animals had a higher plasma hydrogen per
oxide concentration compared with their normotensive counterparts (2.8
1+/-0.43 versus 2.10+/-0.41 mu mol/L), while no difference was detecte
d between high- and low salt-treated Dahl-R animals (1.70+/-0.35 versu
s 1.56+/-0.51 mu mol/L). The plasma hydrogen peroxide levels of all gr
oups correlated with mean arterial pressure (r=.77). These findings de
monstrate an enhanced production of oxygen free radicals in the microv
asculature of hypertensive Dahl-S rats.