Increased O2•- production and upregulation of ETB receptors by sympathetic neurons in DOCA-salt hypertensive rats

Superoxide anion (O-2(.-)) production is elevated in the vasculature of hypertensive animals but it is not known if O-2(.-) production is also elevated in the sympathetic nervous system. We measured O-2(.-) levels in prevertebral sympathetic ganglia of deoxycorticosterone acetate (DOCA)-salt hypertensive rats using the dihydroethidine (DHE) fluorescence method. O-2(.-) was elevated in ganglia from DOCA-salt rats compared with normotensive sham rats. Treatment of ganglia with endothelin (ET)-1 ( 3 x 10(-8) mol/L) resulted in a 200% increase in fluorescence intensity in neurons, which was attenuated by the ETB receptor antagonist BQ788 (10(-7) mol/L). ET-1 also increased the O-2(.-) induced fluorescence in dissociated sympathetic neurons and PC-12 cells via activation of ETB receptors, but not ETA receptors. To evaluate whether elevated ET- 1 levels in the ganglia might contribute to the elevated O-2(.-) 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 ETB receptor levels in ganglia from sham and DOCA-salt animals. ETB receptor mRNA levels were 32% higher and ETB receptor protein levels were 20% higher in celiac ganglia from DOCA-salt rats than from sham rats separately. In conclusion, O-2(.-) is elevated in prevertebral sympathetic ganglia in DOCA-salt hypertension, and ET- 1 is a potent stimulus for the elevation of O-2(.-) levels in sympathetic ganglia, an effect that may be mediated by the upregulation of ETB receptors.