Increased O ₂ ^·− Production and Upregulation of ET _B Receptors by Sympathetic Neurons in DOCA-Salt Hypertensive Rats

Abstract

Abstract-Superoxide anion (O 2·Ϫ ) production is elevated in the vasculature of hypertensive animals but it is not known if O 2 ·Ϫ production is also elevated in the sympathetic nervous system. We measured O 2 ·Ϫ levels in prevertebral sympathetic ganglia of deoxycorticosterone acetate (DOCA)-salt hypertensive rats using the dihydroethidine (DHE) fluorescence method. O 2 ·Ϫ was elevated in ganglia from DOCA-salt rats compared with normotensive sham rats. Treatment of ganglia with endothelin (ET)-1 (3ϫ10 Ϫ8 mol/L) resulted in a 200% increase in fluorescence intensity in neurons, which was attenuated by the ET B receptor antagonist BQ788 (10 Ϫ7 mol/L). ET-1 also increased the O 2 ·Ϫ induced fluorescence in dissociated sympathetic neurons and PC-12 cells via activation of ET B receptors, but not ET A receptors. To evaluate whether elevated ET-1 levels in the ganglia might contribute to the elevated O 2 ·Ϫ found in ganglia we measured the amount of ET-1 using an ELISA assay. ET-1 levels in sham rat celiac ganglia were 695.6Ϯ40.9 picogram per gram; they were not different than ET-1 levels in ganglia from DOCA-salt rats. We then compared ET B receptor levels in ganglia from sham and DOCA-salt animals. ET B receptor mRNA levels were 32% higher and ET B receptor protein levels were 20% higher in celiac ganglia from DOCA-salt rats than from sham rats separately. In conclusion, O 2 ·Ϫ is elevated in prevertebral sympathetic ganglia in DOCA-salt hypertension, and ET-1 is a potent stimulus for the elevation of O 2 ·Ϫ levels in sympathetic ganglia, an effect that may be mediated by the upregulation of ET B receptors. Key Words: endothelin Ⅲ receptors, endothelin Ⅲ hypertension Ⅲ sympathetic nervous system Ⅲ oxidative stress M any factors are potentially responsible for the changes that occur in the sympathetic nervous system in hypertension. In vascular tissue, there is a profound increase in reactive oxygen species (ROS), including superoxide anion (O 2 ·Ϫ ), in several models of hypertension. 1,2 However, it is not known whether sympathetic neurons generate ROS, such as O 2 ·Ϫ , and whether this is elevated in hypertension as it is in the vascular system. ROS contribute to oxidative damage and cell death in neurodegenerative diseases such as amyotropic lateral sclerosis and Parkinson disease. 3 But there is no evidence of degenerative changes in sympathetic ganglia in hypertension. In the central nervous system ROS can serve as signaling molecules mediating the effects of neuroactive substances. For example, angiotensin II (Ang II)/ROS signaling system mediates the action of Ang II to increase blood pressure. 4 Endothelin-1 (ET-1), a peptide originally described as a potent vasoconstrictor synthesized in endothelial cells, is also present in the nervous system and has multiple actions on sympathetic and sensory neurons. 5-7 ET-1 contributes to salt-sensitive hypertension in animals and humans, 8 and the pathogenesis is associated with ROS, especially O 2 ·Ϫ , which are increased in the blood vessels in deoxycorticosterone ...

Superoxide anion is elevated in sympathetic neurons in DOCA-salt hypertension via activation of NADPH oxidase

“…Particularly, with the consideration of a high sympathetic outflow present in hypertension (2), such as in DOCA-salt hypertensive rats (39), ROS-activated PKC may result in elevated neurotransmitter release from nerve terminals innervating blood vessels and, accordingly, increase blood pressure. O 2 Ϫ ⅐ levels are higher in sympathetic ganglia from DOCAsalt hypertensive rats than from sham rats (9), and this increase may come from the increased NADPH oxidase activity. NADPH oxidase activity was higher in CG homogenates from DOCA-salt hypertensive rats compared with normotensive rats.…”

“…For example, there is more endothelial ET-1 mRNA and higher basal release of endogenous endothelin in DOCA-salt hypertensive rats (32,48), and chronic endothelin receptor blockade treatment decreases blood pressure to the normal range (10). ET-1 is a potential endogenous stimulating factor for O 2 Ϫ ⅐ production in sympathetic ganglia (9). In DOCA-salt hypertensive rats, there is increased expression of ET B receptors, which mediate ET-1 effects in this tissue (9).…”

“…ET-1 is a potential endogenous stimulating factor for O 2 Ϫ ⅐ production in sympathetic ganglia (9). In DOCA-salt hypertensive rats, there is increased expression of ET B receptors, which mediate ET-1 effects in this tissue (9). In carotid arteries, there is more ET-1 mRNA and peptide in endothelial cells in DOCA hypertension, and ET-1 increases vascular NADPH oxidase activity (26).…”

“…Recently, we showed that prevertebral sympathetic ganglion neurons generate O 2 Ϫ ⅐ and that O 2 Ϫ ⅐ production is elevated in hypertension (9). NADPH oxidase was first found and cloned in phagocytes (3).…”

The Vascular Endothelin System in Hypertension - Recent Patents and Discoveries

“…ET B receptors have also been localized in renal tubules and collecting duct epithelial cells, airway smooth muscle, liver hepatocytes, osteoblasts, central and peripheral neurons, multiple endocrine tissues and various cells of the reproductive tract [9,44]. Together ET A and ET B are widely distributed in vascular tissues, the central and sympathetic nervous systems, and some regions of the kidney, such as arterioles, glomerular capillaries and inner medullary collecting ducts [48,49].…”