The rostral ventrolateral medulla (RVLM) is a relay point that provides supraspinal excitatory input to sympathetic preganglionic neurons in the regulation of blood pressure. The importance of the RVLM is further highlighted by observations that an increase of RVLM sensitivity to angiotensin II and enhanced sympathetic activity are associated with hypertension. Angiotensin-converting enzyme 2 (ACE2) has been shown to be central in maintaining the balance between vasoconstrictor activity of angiotensin II with vasoprotective action of angiotensin-(1-7) in the peripheral system. However, its role in central control of blood pressure in the RVLM is yet to be investigated. Thus, our objective in this study was to compare ACE2 expression in the RVLM of Wistar–Kyoto rats and spontaneously hypertensive rats and to determine whether RVLM ACE2 is involved in blood pressure control. ACE2 immunoreactivity was diffusely distributed in many cardiovascular regulatory neurons, including the RVLM. Western blot analysis revealed a 40% decrease in ACE2 in the RVLM of spontaneously hypertensive rat compared with Wistar–Kyoto rats. Lentiviral-mediated overexpression of ACE2 (lenti-ACE2) was used to determine whether a decrease in ACE2 in the RVLM is associated with hypertensive state. Bilateral injection of lenti-ACE2 resulted in a long-term expression of transgenic ACE2. This was associated with a decrease in mean arterial pressure exclusively in the spontaneously hypertensive rat (141±4 mm Hg in lenti-GFP versus 124±5 mm Hg in lenti-ACE2) and heart rate (304±7 bpm in lenti-GFP versus 285±5 bpm in lenti-ACE2). These observations demonstrate that overexpression of ACE2 overcomes its intrinsic decrease in the RVLM and decreases high blood pressure in the spontaneously hypertensive rat.

—The present study examined whether inhibition of P4504A enzyme activity and the formation of 20-HETE contributes to the activation of K⁺channels and vasodilator effects of nitric oxide (NO) in renal arterioles. Addition of an NO donor to the P4504A2 enzyme that produces 20-HETE increased visible light absorbance at 440 nm indicating that NO binds to heme in this enzyme. NO donors also dose-dependently inhibited the formation of 20-HETE in microsomes prepared from renal arterioles. In patch-clamp experiments, NO donors increased the open-state probability of a voltage-sensitive, large-conductance (195±9 pS) K⁺channel recorded with cell-attached patches on renal arteriolar smooth muscle cells. Blockade of guanylyl cyclase with [1H-[1,2,4]Oxadiazolo[4,3-a] quinoxalin-1-one] (ODQ, 10 μmol/L), or cGMP-dependent kinase with 8R,9S,11S-(−)-9-methoxycarbamyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1H,8H,11H-2,7b,11a-trizadibenzo-(a,g)-cy-cloocta-(c,d,e)-trinden-1-one (KT-5823) (1 μmol/L) did not alter the effects of NO on this channel. In contrast, inhibition of the formation of 20-HETE with 17-octadecynoic acid (1 μmol/L) activated this channel and masked the response to NO. Preventing the NO-induced reduction in intracellular 20-HETE levels also blocked the effects of NO on this channel. Sodium nitroprusside (SNP) increased the diameter of renal interlobular arteries preconstricted with phenylephrine to 80±4% of control. Blockade of guanylyl cyclase with ODQ (10 μmol/L) attenuated the response to SNP by 26±2%; however, fixing 20-HETE levels at 100 nmol/L reduced the response by 67±8%. Blockade of both pathways eliminated the response to SNP. These results indicate that inhibition of the formation of 20-HETE contributes to the activation of K⁺channels and the vasodilator effects of NO in the renal microcirculation.

SUMMARY: 1. Arachidonic acid (AA) is metabolized by cytochrome P450 (CYP)‐dependent pathways to epoxyeicosatrienoic acids (EET) and 20‐hydroxyeicosatetraenoic acid (20‐HETE) in the kidney and the peripheral vasculature.2. The present short review summarizes the renal and cardiovascular actions of these important mediators.3. Epoxyeicosatrienoic acids are vasodilators produced by the endothelium that hyperpolarize vascular smooth muscle (VSM) cells by opening Ca²⁺‐activated K⁺ (K_Ca) channels. 20‐Hydroxyeicosatetraenoic acid is a vasoconstrictor that inhibits the opening of K_Ca channels in VSM cells. Cytochrome P450 4A inhibitors block the myogenic response of small arterioles to elevations in transmural pressure and autoregulation of renal and cerebral blood flow in vivo. Cytochrome P450 4A blockers also attenuate the vasoconstrictor response to elevations in tissue PO₂, suggesting that this system may serve as a vascular oxygen sensor. Nitric oxide and carbon monoxide inhibit the formation of 20‐HETE and a fall in 20‐HETE levels contributes to the activation of K_Ca channels in VSM cells and the vasodilator response to these gaseous mediators. 20‐Hydroxyeicosatetraenoic acid also mediates the inhibitory actions of peptide hormones on sodium transport in the kidney and the mitogenic effects of growth factors in VSM and mesangial cells. A deficiency in the renal production of 20‐HETE is associated with the development of hypertension in Dahl salt‐sensitive rats.4. In summary, the available evidence indicates that CYP metabolites of AA play a central role in the regulation of renal, pulmonary and vascular function and that abnormalities in this system may contribute to the pathogenesis of cardiovascular diseases.

—The present study examined the hypothesis that activation of protein kinase C (PKC), components of the mitogen-activated protein (MAP) kinase pathway, or both contributes to the inhibitory effects of 20-hydroxyeicosatetraenoic acid (20-HETE) on K ⁺ -channel activity and its vasoconstrictor response in renal arterioles. 20-HETE (0.1 to 50 μmol/L) dose-dependently produced a 30% increase in PKC activity and a fivefold rise in the expression of active extracellular signal-regulated kinase 1 (ERK1) and ERK2 proteins in renal microvessels. 20-HETE (0.01 to 1 μmol/L) reduced the diameter of isolated perfused renal interlobular arterioles by 33±2%. Blockade of PKC activity with an N-myristoylated PKC pseudosubstrate inhibitor (Myr-PKCi, 100 μmol/L) or calphostin C (0.5 μmol/L) had no significant effect on the vasoconstrictor response to 20-HETE. In contrast, the tyrosine kinase inhibitors genistein (30 μmol/L) and tyrphostin 25 (10 μmol/L) reduced the response to 20-HETE by 76.5±2.1% and 67.5±1.8%, respectively. A specific inhibitor of mitogen-activated extracellular signal-regulated kinase (MEK), PD98059, had no effect on the vasoconstrictor response to 20-HETE. In cell-attached patches on renal vascular smooth muscle cells, 20-HETE reduced the open state probability of a large-conductance K ⁺ channel (from 0.0026±0.0004 to 0.0006±0.0001). The Myr-PKCi (100 μmol/L) did not alter the inhibitory effects of 20-HETE on this channel. In contrast, the tyrosine kinase inhibitor genistein (30 μmol/L) blocked the inhibitory effects of 20-HETE on the large-conductance K ⁺ channel. These data suggest that 20-HETE activates the MAP kinase system in renal arterioles and that the activation of a tyrosine kinase, which is proximal to MEK in this cascade, contributes to the inhibitory effects of 20-HETE on K ⁺ -channel activity and its vasoconstrictor effects in the renal arterioles.