Hypertension
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Excess dietary salt intake contributes to or exacerbates some forms of hypertension by increasing sympathetic nerve activity (SNA) and arterial blood pressure (ABP) through angiotensin II (Ang II) type 1 receptor activation in the rostral ventrolateral medulla (RVLM). Despite this interaction among dietary salt, Ang II, and the RVLM, no studies have directly examined whether dietary salt by itself alters Ang II-dependent responses and regulation of RVLM neurons, SNA, and ABP. Therefore, the present study directly tested this hypothesis. ⋯ Blockade of iontotropic glutamate receptors had no effect. Altogether, these findings suggest that elevated dietary salt enhances the sympathoexcitatory actions of Ang II in the RVLM via changes in the intrinsic properties of RVLM neurons. Moreover, elevated dietary salt intake differentially affects the tonic activity of the peripheral versus brain RVLM Ang II type 1 receptors to regulate baseline SNA and ABP.
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Prostaglandin (PG) E(2) has an established role in the regulation of vascular tone and reactivity. The present study examined the role and mechanism of microsomal PG synthase-1 (mPGES-1) in vascular response to angiotensin II (Ang II) infusion. A 7-day Ang II infusion at 0.35 mg/kg per day via osmotic minipump had no obvious effect on mean arterial blood pressure in mPGES-1(+/+) mice but induced a marked hypertensive response in mPGES-1(-/-) mice, associated with a parallel increase in urinary 8-isoprostane excretion and aortic NADPH oxidase activity and mRNA expression of p47(phox), gp91(phox), and Nox1. ⋯ In cultured vascular smooth muscle cells, Ang II exerted a direct stimulatory effect on reactive oxygen species production, NADPH oxidase activity, and expression of p47(phox), gp91(phox), and Nox1 that were all inhibited by PGE(2). The -/- mice also exhibited enhanced renal hemodynamic response to acute Ang II infusion at 150 nmol/kg per minute via a jugular vein over a period of 40 minutes. These results suggest that mPGES-1-derived PGE(2) buffers Ang II-induced vasoconstriction via inhibition of NADPH oxidase-dependent reactive oxygen species production.