Abstract P337: Angiotensin 1-7 Mitigates Oxidative Stress, Protects Renal Dopamine D1 Receptor Function and Prevents Development of Hypertension

The role of angiotensin in etiology of cardiovascular diseases especially in hypertension is well established. Renin-angiotensin-aldosterone contributes to the development and maintenance of hypertension directly by increases in vascular tone and renal sodium reabsorption or indirectly by increasing oxidative stress and inflammation. Contrary to this pathological arm, angiotensin (Ang) 1-7 via Mas receptors has been reported to protect the cardiovascular function although the exact mechanism is not yet clear. We have previously shown that oxidative stress leads to renal dopamine D1 receptor (D1R) dysfunction which could disrupt sodium regulation and subsequently lead to hypertension. In here we wanted to test whether chronic administration of Ang 1-7 in mice could mitigate oxidative stress, protect renal D1R function and prevent development of hypertension. Mice (C57BL) were implanted with telemetry probes and concomitantly treated with L-buthionine sulfoximine (BSO, in drinking water) and Ang 1-7 (via jugular vein by osmotic pumps). Control (C, no treatment) and shams (implanted with saline filled pumps) exhibited similar behavioral and physiological parameters. Mice treated with BSO alone exhibited increased oxidative stress and high BP as compared to controls. Ang 1-7 treatment did not affect oxidative stress and BP in control mice but prevented the increase in BP and oxidative milieu in BSO treated mice. Mean arterial pressure (mmHg), C: 78.5 ± 2.3*; BSO: 97.3 ± 3.8; Ang 1-7: 80.1* ± 4.1; BSO+Ang 1-7: 83.2 ± 3.4*, *P <0.05 vs BSO. SKF38393, a D1R agonist, increased urine and sodium excretion in control mice but failed to induce diuresis or natriuresis in BSO-treated mice. Treatment with Ang 1-7 protected D1R function as both natriuresis and diuresis was observed in mice treated with BSO plus Ang 1-7. Chronic Ang 1-7 had no effect on D1R function in the absence of BSO. These data show that oxidative stress leads to hypertension by disrupting renal D1R dependent sodium regulation. Ang 1-7 mitigates oxidative stress, protects renal D1R function and prevents increase in BP. This study provides a new insight on how beneficial arm of Ang system could protect renal D1R-mediated sodium regulation and prevent development of hypertension during oxidative stress.

Genetics of hypertension: discoveries from the bench to human populations

Hypertension is a complex trait that is influenced by both heritable and environmental factors. The search for genes accounting for the susceptibility to hypertension has driven parallel efforts in human research and in research using experimental animals in controlled environmental settings. Evidence from rodent models of genetic hypertension and human Mendelian forms of hypertension and hypotension have yielded mechanistic insights into the pathways that are perturbed in blood pressure homeostasis, most of which converge at the level of renal sodium reabsorption. However, the bridging of evidence from these very diverse approaches to identify mechanisms underlying hypertension susceptibility and the translation of these findings to human populations and public health remain a challenge. Furthermore, findings from genome-wide association studies still require functional validation in experimental models. In this review, we highlight results and implications from key studies in experimental and clinical hypertension to date.

Renal redox response to normal pregnancy in the rat

Normal pregnancy involves increased renal sodium reabsorption, metabolism, and oxygen consumption, which can cause increased oxidative stress (OS). OS can decrease nitric oxide (NO) bioavailability and cause pregnancy complications. In this study we examined the NO synthases (NOS) and redox state in the kidney cortex and aorta in early (E), mid (M), and late (L) pregnant (P) ( days 3, 12, 20) and 2–4 days postpartum (PP) rats compared with virgin rats (V). Protein abundance of endothelial NOS (eNOS) was unchanged and neuronal NOS (nNOS)α fell at LP in the kidney cortex. Kidney cortex nNOSβ was elevated at MP, LP, and PP. No changes in aortic NOS isoforms were observed. Kidney cortex nitrotyrosine (NT) abundance decreased in EP, MP, and PP, whereas aortic NT increased in EP, MP, and PP. The NADPH oxidase subunit p22phox decreased in the kidney cortex at EP while aortic p22phox increased in EP and LP. No changes in kidney cortex NADPH-dependent superoxide production or hydrogen peroxide levels were noted. Kidney cortex cytosolic (CuZn) superoxide dismutase (SOD) was unchanged, while mitochondrial SOD decreased at EP and extracellular SOD decreased at MP and LP in the kidney cortex. Despite falls in abundance of kidney cortex SODs, total antioxidant capacity (TAC) was elevated in EP, MP, and PP in the kidney cortex. Aortic CuZn SOD deceased at PP, while the other aortic SODs and aortic TAC did not change. Data from this study suggest that the kidney cortex is protected from OS during normal rat pregnancy via an increase in antioxidant activity.

Renal sodium transporter/channel expression and sodium excretion in P2Y2 receptor knockout mice fed a high-NaCl diet with/without aldosterone infusion

The P2Y2 receptor (P2Y2-R) antagonizes sodium reabsorption in the kidney. Apart from its effect in distal nephron, hypothetically, P2Y2-R may modulate activity/abundances of sodium transporters/channel subunits along the nephron via antagonism of aldosterone or vasopressin or interaction with mediators such as nitric oxide (NO), and prostaglandin E2 (PGE2) or oxidative stress (OS). To determine the extent of the regulatory role of P2Y2-R in renal sodium reabsorption, in study 1, we fed P2Y2-R knockout (KO; n = 5) and wild-type (WT; n = 5) mice a high (3.15%)-sodium diet (HSD) for 14 days. Western blotting revealed significantly higher protein abundances for cortical and medullary bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2), medullary α-1-subunit of Na-K-ATPase, and medullary α-subunit of the epithelial sodium channel (ENaC) in KO vs. WT mice. Molecular analysis of urine showed increased excretion of nitrates plus nitrites (NOx), PGE2, and 8-isoprostane in the KO, relative to WT mice, supporting a putative role for these molecules in determining alterations of proteins involved in sodium transport along the nephron. To determine whether genotype differences in response to aldosterone might have played a role in these differences due to HSD, in study 2 aldosterone levels were clamped (by osmotic minipump infusion). Clamping aldosterone (with HSD) led to significantly impaired natriuresis with elevated Na/H exchanger isoform 3 in the cortex, and NKCC2 in the medulla, and modest but significantly lower levels of NKCC2, and α- and β-ENaC in the cortex of KO vs. WT mice. This was associated with significantly reduced urinary NOx in the KO, although PGE2 and 8-isoprostane remained significantly elevated vs. WT mice. Taken together, our results suggest that P2Y2-R is an important regulator of sodium transporters along the nephron. Pre- or postreceptor differences in the response to aldosterone, perhaps mediated via prostaglandins or changes in NOS activity or OS, likely play a role.