Activation of ET_B receptors increases superoxide levels in sympathetic ganglia in vivo

Abstract

) found that endothelin (ET) stimulated O 2 Ϫ production in sympathetic ganglion neurons in vitro by activating ETB receptors. The objective of the present study was to determine whether activation of ETB receptors in vivo elevates O 2 Ϫ levels in sympathetic ganglia. Because ET B receptor activation increases blood pressure, we also sought to determine whether alteration in O 2 Ϫ levels was a direct effect of ET B receptor activation on sympathetic ganglia or an indirect consequence of hypertension. Male Sprague-Dawley rats received intravenous infusions of either the specific ET B receptor agonist sarafotoxin 6c (S6c; 5 pmol ⅐ kg Ϫ1 ⅐ min Ϫ1 ) or isotonic saline at 0.01 ml/min (control) for 120 min. To measure O 2 Ϫ levels, we removed the inferior mesenteric ganglion immediately after infusion and stained it with dihydroethidine (DHE). Mean arterial pressure increased 26.6 Ϯ 1.7 mmHg in the S6c-treated rats and 3.65 Ϯ 6 mmHg in control rats. Measurements of average pixel intensity revealed that the DHE fluorescence in ganglionic neurons and surrounding glial cells were 96.7% and 160% greater in S6c-treated than in control rats, respectively. To evaluate the effect of elevated blood pressure on O 2 Ϫ production, a separate group of rats received phenylephrine (PE; 10 g ⅐ kg Ϫ1 ⅐ min Ϫ1 iv) for 2 h. MAP increased 31 Ϯ 1.2 mmHg in PE-infused rats. The DHE fluorescence intensity in ganglia of PEinfused rats was significantly greater than that of control rats, 137.7% in neurons and 104.6% in glia but significantly lower than in ganglia from S6c rats. We conclude that ETB receptor activation in vivo significantly enhances O 2 Ϫ levels in sympathetic ganglia, due to both pressor effects and direct stimulation of ET B receptors in ganglion cells. hypertension; sarafotoxin 6c; sympathetic nervous activity; oxidative stress; reactive oxygen species HYPERTENSION CAUSED BY NUMEROUS genetic and neurohumoral factors is associated with higher amounts of reactive oxygen species (ROS) in blood vessels, brain, and kidneys; examples include ANG II-mediated hypertension, deoxycorticosterone acetate (DOCA)-salt hypertension, mineralocorticoid hypertension, aortic banding-induced hypertension, renovascular hypertension, and endothelin-induced hypertension (1, 3, 18 -20, 23, 28, 36, 42). The best characterized ROS in tissues of hypertensive individuals is superoxide anion (O 2 Ϫ ). Reduction in O 2 Ϫ formation can lower blood pressure in some experimental models of hypertension (1,9,14,32,38), suggesting that increased production of ROS is an etiologic factor in hypertension. O 2 Ϫ can increase blood pressure by several mechanisms. In the vasculature, O 2 Ϫ causes vasoconstriction, in part by inducing endothelial cell dysfunction (5). Increased O 2 Ϫ in the kidney is associated with enhanced tubular reabsorption of sodium and water (27,33). In key brain regions, increased O 2 Ϫ leads to increased sympathetic nervous system activity (SNA) (7,(51)(52)(53). The focus of the work to be reported here, however, is on the peripheral sympa...

The Continuing Saga of Neuronal Oxidative Stress in Hypertension

“…The article by Cao et al, 5 published in this issue of Hypertension, is one of a series of articles from this group 6 -8 that describe NAD(P)H oxidase expression and regulation of ROS production in sympathetic neurons located in prevertebral sympathetic ganglia of normotensive and hypertensive (deoxycorticosterone acetate [DOCA]-salt) rats. The present results confirm earlier findings that Nox1, Nox2, Nox4, p22 phox , and p47 phox are expressed in sympathetic ganglia [7][8][9] and that NAD(P)H oxidase activity in these ganglia is increased in DOCA-salt hypertension. 7 Two important novel findings of this study are that Nox subunits are differentially expressed in sympathetic versus sensory dorsal root ganglia (DRGs) with Nox4 expression being low in DRGs and relatively high in sympathetic ganglia and that NAD(P)H oxidase activity is decreased in hypertensive DRGs, an effect opposite to that seen in sympathetic ganglia 5 (see Figure).…”

“…8 Exposure of ganglia to phenylephrine in vitro did not increase superoxide. 8 Studies in my laboratory have recently demonstrated increases in NAD(P)H oxidase expression (Nox2, p22 phox , p47 phox , and p67 phox ) and superoxide in sympathetic ganglia of apolipoprotein E-deficient mice with hypercholesterolemia.…”

“…8 Exposure of ganglia to phenylephrine in vitro did not increase superoxide. 8 Studies in my laboratory have recently demonstrated increases in NAD(P)H oxidase expression (Nox2, p22 phox , p47 phox , and p67 phox ) and superoxide in sympathetic ganglia of apolipoprotein E-deficient mice with hypercholesterolemia. 9 Preliminary results indicate that the high NAD(P)H oxidase expression in the normotensive apolipoprotein E-deficient mice is abrogated by 2-week treatment with the Ang II receptor subtype 1 receptor blocker losartan suggesting that the oxidative stress is not related to blood pressure, per se, but is driven by Ang II.…”

Chronic Activation of Endothelin B Receptors

“…We showed recently that infusion of S6c into rats causes increased concentrations of reactive oxygen species in sympathetic ganglia, which might serve to facilitate ganglionic transmission and thereby sympathetic arterial vasoconstrictor activity. 18 The possibility of sympathetically mediated blood pressure responses via ET B R stimulation is supported by earlier work from Pollock et al 37 They demonstrated that acute infusion of S6c still causes pressor responses in rats lacking functional ET B R in all tissues except those containing dopamine-␤-hydroxylase (such as sympathetic neurons).…”

“…18 Antimicrobial prophylaxis and postoperative analgesia were achieved by administration of ticarcillinclavulanate (200 mg/kg IP) and enrofloxacin (5 mg/kg IP) and buprenorphine (0.05 mg/kg SC), respectively. Rats recovered from anesthesia, under close observation, on a heating pad.…”