Endothelin activation of reactive oxygen species mediates stress-induced pressor response in Dahl salt-sensitive prehypertensive rats

Abstract

Experiments were designed to test the hypothesis that endothelin (ET) and/or reactive oxygen species contribute to the pressor response induced by acute air jet stress in normotensive Dahl salt-sensitive rats maintained on a normal salt diet (prehypertensive). Mean arterial pressure was chronically monitored by telemetry before and after 3-day treatment with the free radical scavenger 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl (Tempol) or ET receptor antagonists ABT-627 (ET A antagonist) or A-182086 (ET A/B antagonist) supplied in the drinking water. Rats were restrained and subjected to pulsatile air jet stress (3 minutes). Plasma samples at baseline and during acute stress were analyzed for 8-isoprostane (measure of reactive oxygen species production) and ET. Neither Tempol nor ET receptor antagonist treatment had an effect on baseline mean arterial pressure or plasma 8-isoprostane. The pressor response to acute stress was accompanied by significant increases in plasma 8-isoprostane and ET. Tempol significantly reduced both the total pressor response (area under the curve) and the stress-mediated increase in plasma 8-isoprostane; conversely, Tempol had no effect on the stress-induced increase in plasma ET. Combined ET(A/B) antagonism, but not selective ET(A) receptor blockade, similarly suppressed the pressor response to stress and stress-mediated rise in 8-isoprostane. Together these results indicate that reactive oxygen species contribute to the pressor response to acute air jet stress. Furthermore, the increase in reactive oxygen species occurs downstream of ET(B) receptor activation.

Figure 1

Summary of integrated pressor response (area under the curve; AUC) to acute air jet stress (left panel) and integrated mean arterial pressure during the 20-minute post-stress period (right panel) in pre-hypertensive Dahl salt-sensitive rats. Animals were either untreated (week 1) or given the free radical scavenger, tempol, (1 mM in the drinking water; week 2) (n=10) for 3 days. AUC was calculated as the sum of the mean arterial pressure data points during or post-air jet stress minus the average MAP obtained over the 3 minutes before the start of air jet stress. *p<0.05

Figure 2

Effect of the free radical scavenger, tempol, on plasma concentrations of 8-isoprostane (A) (n=7–12) and endothelin-1 (ET-1) (B) (n=6–11) at baseline (unstressed) and during air jet stress in pre-hypertensive Dahl salt-sensitive rats. Animals were either untreated (week 1) or given tempol (1 mM in the drinking water; week 2) for 3 days. *p<0.05

Figure 3

Effect of the free radical scavenger, tempol, on plasma concentration of epinephrine (Epi) (A) and norepinephrine (NE) (B) (n=7 each) at baseline (unstressed) and during air jet stress Dahl salt-sensitive rats. Animals were either untreated (week 1) or given tempol (1 mM in the drinking water; week 2) for 3 days. *p<0.05

Figure 4

Effect of the selective endothelin A receptor antagonist ABT-627 (A) (n=15–18) and the dual endothelin A/B receptor antagonist A-182086 (B) (n=13) on plasma concentrations of 8-isoprostane at baseline (unstressed) and during air jet stress in pre-hypertensive Dahl salt-sensitive rats. Animals were either untreated (week 1), or given ABT-627 (5 mg/kg/day in the drinking water; week 2) or A-182086 (30 mg/kg/day in the food; week 2) for 3 days. *p<0.05

Figure 5

Summary of integrated pressor response (area under the curve; AUC) to acute air jet stress (left panel) and integrated mean arterial pressure during the 20-minute post-stress period (right panel) in pre-hypertensive Dahl salt-sensitive rats. Animals were either untreated (week 1) or given the dual endothelin A/B receptor antagonist, A-182086 (30 mg/kg/day in the food; week 2) (n=4) for 3 days. AUC was calculated as the sum of the mean arterial pressure data points during or post-air jet stress minus the average MAP obtained over the 3 minutes before the start of air jet stress. *p<0.05

Figure 6

Scheme depicting the causal relationship of the ET pathway and ROS production in the acute stress-mediated rise in blood pressure in pre-hypertensive DS rats.