Increased O2·−Production and Upregulation of ETBReceptors by Sympathetic Neurons in DOCA-Salt Hypertensive Rats

Superoxide anion (O2·−) production is elevated in the vasculature of hypertensive animals but it is not known if O2·−production is also elevated in the sympathetic nervous system. We measured O2·−levels in prevertebral sympathetic ganglia of deoxycorticosterone acetate (DOCA)-salt hypertensive rats using the dihydroethidine (DHE) fluorescence method. O2·−was elevated in ganglia from DOCA-salt rats compared with normotensive sham rats. Treatment of ganglia with endothelin (ET)-1 (3×10−8mol/L) resulted in a 200% increase in fluorescence intensity in neurons, which was attenuated by the ETBreceptor antagonist BQ788 (10−7mol/L). ET-1 also increased the O2·−induced fluorescence in dissociated sympathetic neurons and PC-12 cells via activation of ETBreceptors, but not ETAreceptors. To evaluate whether elevated ET-1 levels in the ganglia might contribute to the elevated O2·−found in ganglia we measured the amount of ET-1 using an ELISA assay. ET-1 levels in sham rat celiac ganglia were 695.6±40.9 picogram per gram; they were not different than ET-1 levels in ganglia from DOCA-salt rats. We then compared ETBreceptor levels in ganglia from sham and DOCA-salt animals. ETBreceptor mRNA levels were 32% higher and ETBreceptor protein levels were 20% higher in celiac ganglia from DOCA-salt rats than from sham rats separately. In conclusion, O2·−is elevated in prevertebral sympathetic ganglia in DOCA-salt hypertension, and ET-1 is a potent stimulus for the elevation of O2·−levels in sympathetic ganglia, an effect that may be mediated by the upregulation of ETBreceptors.