Low-dose angiotensin II supplementation restores flow-induced dilation mechanisms in cerebral arteries of Sprague-Dawley rats on a high salt diet.

OBJECTIVE: Salt-induced suppression of angiotensin II contributes to impaired endothelium-dependent vascular reactivity. The present study investigated the effect of chronic low-dose angiotensin II (ANG II) supplementation on the mechanisms of flow-induced dilation (FID) and oxidative stress at the cellular and molecular level in middle cerebral arteries (MCA) of male Sprague-Dawley rats fed high salt diet. METHODS: Rats (10 weeks old) were randomly assigned to a low salt diet group (0.4% NaCl in rat chow); high salt diet group (7 days 4% NaCl in rat chow) or HS+ANG II group [7 days high salt diet with 3 days ANG II administration via osmotic minipumps (100 ng/kg per min on days 4-7)]. FID was determined in absence/presence of the NOS inhibitor L-NAME, the non-selective cyclooxygenase (COX-1,2) inhibitor indomethacin, a selective inhibitor of CYP450 epoxygenase activity (MS-PPOH) and the superoxide dismutase mimetic TEMPOL. Gene expression of antioxidative enzymes, and of genes and proteins involved in FID mechanisms were determined by RT-qPCR and western blot. Vascular nitric oxide and superoxide/reactive oxygen species levels were assessed by direct fluorescence. Serum systemic oxidative stress parameters were measured by spectrophotometry. RESULTS: Chronic low-dose ANG II supplementation in high salt fed rats restored FID of MCAs, which was nitric oxide, prostanoid and epoxyeicosatrienoic acid dependent. ANG II changed the protein/gene expression of COXs, HIF-1α and VEGF and significantly increased GPx4 and EC-SOD antioxidative enzyme expression, decreased systemic oxidative stress, decreased superoxide/ROS levels and increased nitric oxide bioavailability in the vascular wall. CONCLUSION: Physiological levels of circulating ANG II are crucial to maintain the HIF-1α dependent mechanisms of FID and vascular oxidative balance without affecting mean arterial pressure.

NRF2 activation with Protandim attenuates salt-induced vascular dysfunction and microvascular rarefaction.

HYPOTHESIS: This study tested the hypothesis that dietary activation of the master antioxidant and cell protective transcription factor nuclear factor, erythroid -2-like 2 (NRF2), protects against salt-induced vascular dysfunction by restoring redox homeostasis in the vasculature. METHODS: Male Sprague-Dawley rats and Syrian hamsters were fed a HS (4.0% NaCl) diet containing ~60 mg/kg/day Protandim supplement for 2 weeks and compared to controls fed HS diet alone. RESULTS: Protandim supplementation restoredendothelium-dependent vasodilation in response to acetylcholine (ACh) in middle cerebral arteries (MCA)of HS-fed rats and hamster cheek pouch arterioles, and increased microvessel density in the cremastermuscle of HS-fed rats. The restored dilation to ACh in MCA of Protandim-treated rats was prevented by inhibiting nitric oxide synthase (NOS) with L-NAME [100 µM] and was absent in MCA from Nrf2(-/-) knockout rats fed HS diet. Basilar arteries from HS-fed rats treated with Protandim exhibited significantly lower staining for mitochondrial oxidizing species than untreated animals fed HS diet alone; and Protandim treatment increased MnSOD (SOD2) protein expression in mesenteric arteries of HS-fed rats. CONCLUSIONS: These results suggest that dietary activation of NRF2 protects against salt-induced vascular dysfunction, vascular oxidative stress, and microvascular rarefaction by upregulating antioxidant defenses and reducing mitochondrial ROS levels.