Abstract-Hypertension is considered a low-grade inflammatory condition induced by various proinflammatory cytokines, including tumor necrosis factor (TNF)-␣. Recent studies have implicated an involvement of TNF-␣ in the development of salt-sensitive hypertension induced by angiotensin II (Ang II). To understand further the relationship between TNF-␣ and Ang II, we examined the responses to Ang II in TNF-␣ knockout (TNF-␣ Ϫ/Ϫ ) mice in the present study. A continuous infusion of Ang II (1 g/kg per minute) for 2 weeks was given to both TNF-␣ Ϫ/Ϫ and wild-type (WT) mice with implanted osmotic minipumps. Daily measurement of water intake, salt intake, and urine output were performed using metabolic cages. Blood pressure was monitored continuously with implanted radiotelemetry. Ang II administration for 2 weeks caused increases in salt (0.2Ϯ0.07 to 5.6Ϯ0.95 mL/d) and water (5.4Ϯ0.34 to 11.5Ϯ1.2 mL/d) intake and in mean arterial pressure (115Ϯ1 to 151Ϯ3 mm Hg) in wild-type mice, but these responses were absent in TNF-␣ Ϫ/Ϫ mice (0.2Ϯ0.04 to 0.3Ϯ0.09 mL/d, 5.5Ϯ0.2 to 6.1Ϯ0.07 mL/d, and 113Ϯ2 to 123Ϯ3 mm Hg, respectively). Cardiac hypertrophy induced by Ang II was significantly attenuated in TNF-␣ Ϫ/Ϫ mice compared with wild-type mice. In a group of TNF-␣ Ϫ/Ϫ mice, when replacement therapy was made with recombinant TNF-␣, Ang II induced similar responses in salt appetite, mean arterial pressure, and cardiac hypertrophy, as observed in wild-type mice. These results suggest that TNF-␣ plays a mechanistic role in mediating chronic Ang II-induced effects on salt appetite and blood pressure, as well as on cardiac hypertrophy.

Abstract-The present study was performed to examine the hypothesis that autoregulation-related changes in renal vascular resistance (RVR) are mediated by extracellular ATP. By use of a microdialysis method, renal interstitial concentrations of ATP and adenosine were measured at different renal arterial pressures (RAPs) within the autoregulatory range in anesthetized dogs (nϭ12). RAP was reduced in steps from the ambient pressure (131Ϯ4 mm Hg) to 105Ϯ3 mm Hg (step 1) and 80Ϯ2 mm Hg (step 2). Renal blood flow and glomerular filtration rate exhibited efficient autoregulation in response to these changes in RAP. RVR decreased by 22Ϯ2% in step 1 (PϽ0.01) and 38Ϯ3% in step 2 (PϽ0.01).The control renal interstitial concentration of ATP was 6.51Ϯ0.71 nmol/L and decreased to 4.51Ϯ0.55 nmol/L in step 1 (PϽ0.01) and 2.77Ϯ0.47 nmol/L in step 2 (PϽ0.01). In contrast, the adenosine concentrations (117Ϯ6 nmol/L) were not altered significantly. Changes in ATP levels were highly correlated with changes in RVR (rϭ0.88, PϽ0.0001).Further studies demonstrated that stimulation of the tubuloglomerular feedback (TGF) mechanism by increasing distal volume delivery elicited with acetazolamide also led to increases in renal interstitial ATP concentrations, whereas furosemide, which is known to block TGF responses, reduced renal interstitial fluid ATP concentrations. The data demonstrate a positive relation between renal interstitial fluid ATP concentrations and both autoregulation-and TGF-dependent changes in RVR and thus support the hypothesis that changes in extracellular ATP contribute to the RVR adjustments responsible for the mechanism of renal autoregulation. (Circ Res. 2000;86:656-662.)Key Words: ATP Ⅲ renal autoregulation Ⅲ tubuloglomerular feedback Ⅲ renal interstitium Ⅲ adenosine T he purine nucleotide ATP, an intracellular energy source, is gaining recognition for its paracrine role in regulating skeletal and heart muscle contractility 1,2 as well as vascular tone in several tissues. 1-5 ATP has been shown to be released from endothelial cells, 6 epithelial cells, 7 smooth muscle cells, 6,8 myocardium, 9 and perivascular nerves. 10 Extracellular ATP exerts a substantial influence on hemodynamic function, acting via P2 purinoceptors, on a variety of tissues and organs, 2-5 including the kidney. 4,5,[11][12][13][14][15] A growing body of evidence obtained in both dogs and rats supports the hypothesis that extracellular ATP exerts a role in mediating renal autoregulatory vascular resistance responses, 14 -18 which are caused by active adjustments of vascular smooth muscle tone, primarily in the afferent arterioles. 14,15 Studies using the isolated blood-perfused juxtamedullary nephron preparation demonstrated that ATP, superfused over the renal microvessels, exerts selective afferent arteriolar vasoconstriction without affecting efferent arteriolar tone, 19,20 which is an important criterion for the agent mediating autoregulatory behavior. 14,15 This occurrence is due to the selective localization of P2 purinoceptors, which have...

Experimental evidence has now been amassed to indicate that inhibition of nitric oxide (NO) synthase reduces total or regional renal blood flow by approximately 25 to 30% and markedly increases the renal vascular resistance, demonstrating that basal release of NO helps to maintain the relatively low vascular resistance that is characteristic for the kidney. It has been demonstrated that intraarterial administration of NO synthase inhibitors causes marked reductions in sodium excretion without changes in filtered load and suppressed the arterial pressure-induced natriuretic responses in the kidney. We also demonstrated that a constant rate infusion of a NO donor in dogs pretreated with a NOS inhibitor resulted in increases in sodium excretion but failed to restore the slope of the relation between arterial pressure and sodium excretion, suggesting that an alteration in intrarenal NO production rate during changes in arterial pressure is involved in the mediation of pressure natriuresis. Further experiments in dogs performed in our laboratory have confirmed that there is a direct relationship between changes in arterial pressure and intrarenal NO activity measured using NO-sensitive microelectrodes in the renal tissue. These arterial pressure-induced changes in intrarenal NO activity were seen positively correlated with the changes in urinary excretion rates of sodium. Collectively, these data suggest that acute changes in arterial pressure alter intrarenal NO production, which inhibits tubular sodium reabsorption to manifest the phenomenon of pressure natriuresis.

. In one group of dogs (n ϭ 10), tempol infusion alone for 30 min before NLA infusion did not cause any significant changes in renal blood flow (RBF; 5.2 Ϯ 0.4 to 5.0 Ϯ 0.4 ml ⅐ min Ϫ1 ⅐ g Ϫ1 ), glomerular filtration rate (GFR; 0.79 Ϯ 0.04 to 0.77 Ϯ 0.04 ml ⅐ min Ϫ1 ⅐ g Ϫ1 ), urine flow (V; 13.6 Ϯ 2.1 to 13.9 Ϯ 2.5 l ⅐ minInterestingly, when tempol was infused in another group of dogs (n ϭ 12) pretreated with NLA, it caused increases in V (4.4 Ϯ 0.4 to 9.7 Ϯ 1.4 l⅐min Ϫ1 ⅐g Ϫ1) and in UNaV (0.7 Ϯ 0.1 to 1.3 Ϯ 0.2 mol⅐min Ϫ1 ⅐g Ϫ1 ) without affecting RBF or GFR. Although NO inhibition caused usual qualitative responses in both groups of dogs, the antidiuretic (47 Ϯ 5 vs. 26 Ϯ 4%) and antinatriuretic (67 Ϯ 4 vs. 45 Ϯ 11%) responses to NLA were seen much less in dogs pretreated with tempol. NLA infusion alone increased urinary excretion of 8-isoprostane (13.9 Ϯ 2.7 to 22.8 Ϯ 3.6 pg ⅐ min Ϫ1 ⅐ g Ϫ1

Tumor necrosis factor-α (TNF-α) has been implicated in the pathogenesis of hypertension and renal injury. However, the direct effects of TNF-α on renal hemodynamic and excretory function are not yet clearly defined. We examined the renal responses to infusion of TNF-α (0.33 ng·g−1·min−1) in anesthetized mice. Renal blood flow (RBF) and glomerular filtration rate (GFR) were determined by PAH and inulin clearance. The urine was collected from a cannula inserted into the bladder. Following the 60-min control clearance period, TNF-α infusion was initiated and 15 min were given for stabilization followed by another 60-min clearance period. TNF-α alone (n = 7) caused decreases in RBF (7.9 ± 0.3 to 6.4 ± 0.3 ml·min−1·g−1) and GFR (1.04 ± 0.06 to 0.62 ± 0.08 ml·min−1·g−1) as well as increases in absolute (0.8 ± 0.3 to 1.4 ± 0.3 μmol·min−1·g−1) and fractional excretion of sodium (0.5 ± 0.2 to 1.5 ± 0.4%) without affecting arterial pressure. TNF-α also increased 8-isoprostane excretion (8.10 ± 1.09 to 11.13 ± 1.34 pg·min−1·g−1). Pretreatment with TNF-α blocker etanercept (5 mg/kg sc; 24 and 3 h before TNF-α infusion; n = 6) abolished these responses. However, TNF-α induced an increase in RBF and caused attenuation of the GFR reduction in mice pretreated with superoxide (O2−) scavenger tempol (2 μg·g−1·min−1; n = 6). Pretreatment with nitric oxide (NO) synthase inhibitor nitro-l-arginine methyl ester (0.1 μg·g−1·min−1; n = 6) resulted in further enhancement in vasoconstriction while natriuresis remained unaffected in response to TNF-α. These data suggest that TNF-α induces renal vasoconstriction and hypofiltration via enhancing the activity of O2− and thus reducing the activity of NO. The natriuretic response to TNF-α is related to its direct effects on tubular sodium reabsorption.

Abstract-To examine the potential role of superoxide anion (O 2 Ϫ ) and its interaction with NO in the regulation of renal hemodynamics and excretory function, we have evaluated the renal responses to enhancement in O 2 Ϫ activity before and during NO synthase inhibition in anesthetized dogs (nϭ6). Intraarterial infusion of a superoxide dismutase (SOD) inhibitor, diethyldithiocarbamate (DETC; 0.1 and 0.5 mg/kg per min) was made to enhance O 2 Ϫ activity in the kidney. Cortical (CBF), medullary (MBF), and total renal blood flow (RBF) responses were assessed using laser-Doppler needle flow probes and an electromagnetic flow probe. DETC caused dose-dependent changes in renal parameters, which were recovered within 30 minutes after the termination of DETC infusion. The high-dose infusion of DETC for 25 minutes resulted in an increase of 29Ϯ10% in renal vascular resistance (control, 35.4Ϯ4.4 mm Hg/mL per min per g) and decreases of 21Ϯ5% in RBF (control, 3.5Ϯ0.5 mL/min per g), 20Ϯ5% in CBF, 21Ϯ7% in MBF, 62Ϯ11% in urine flow (control, 10.5Ϯ2.2 L/min per g), and 47Ϯ11% in sodium excretion (control, 2.1Ϯ0.2 mol/min per g), without a significant change (Ϫ10Ϯ6%) in glomerular filtration rate (control, 0.74Ϯ0.09 mL/min per g). During NO synthase inhibition with intraarterial administration of nitro-L-arginine (50 g/kg per min), the same dose of DETC showed a greater increase in renal vascular resistance (73Ϯ15%) and reductions in RBF (39Ϯ4%), CBF (32Ϯ5%), MBF (34Ϯ6%), urine flow (78Ϯ5%), and sodium excretion (67Ϯ10%), with a marked reduction in glomerular filtration rate (59Ϯ7%

Lara LS, McCormack M, Semprum-Prieto LC, Shenouda S, Majid DS, Kobori H, Navar LG, Prieto MC. AT1 receptormediated augmentation of angiotensinogen, oxidative stress, and inflammation in ANG II-salt hypertension. Am J Physiol Renal Physiol 302: F85-F94, 2012. First published September 7, 2011 doi:10.1152/ajprenal.00351.2011.-Augmentation of intrarenal angiotensinogen (AGT) synthesis, secretion, and excretion is associated with the development of hypertension, renal oxidative stress, and tissue injury during ANG II-dependent hypertension. High salt (HS) exacerbates hypertension and kidney injury, but the mechanisms remain unclear. In this study, we determined the consequences of HS intake alone compared with chronic ANG II infusion and combined HS plus ANG II on the stimulation of urinary AGT (uAGT), renal oxidative stress, and renal injury markers. Sprague-Dawley rats were subjected to 1) a normal-salt diet [NS, n ϭ 5]; 2) HS diet [8% NaCl, n ϭ 5]; 3) ANG II infusion in NS rats [ANG II 80 ng/min, n ϭ 5]; 4) ANG II infusion in HS rats [ANG IIϩHS, n ϭ 5]; and 5) ANG II infusion in HS rats treated with ANG II type 1 receptor blocker (ARB) [ANG IIϩHSϩARB, n ϭ 5] for 14 days. Rats fed a HS diet alone did not show changes in systolic blood pressure (SBP), proteinuria, cell proliferation, or uAGT excretion although they did exhibit mesangial expansion, collagen deposition, and had increased NADPH oxidase activity accompanied by increased peroxynitrite formation in the kidneys. Compared with ANG II rats, the combination of ANG II infusion and a HS diet led to exacerbation in SBP (175 Ϯ 10 vs. 221 Ϯ 8 mmHg; P Ͻ 0.05), proteinuria (46 Ϯ 7 vs. 127 Ϯ 7 mg/day; P Ͻ 0.05), and uAGT (1,109 Ϯ 70 vs.. 7,200 Ϯ 614 ng/day; P Ͻ 0.05) associated with greater collagen deposition, mesangial expansion, interstitial cell proliferation, and macrophage infiltration. In both ANG II groups, the O 2 Ϫ levels were increased due to increased NADPH oxidase activity without concomitant increases in peroxynitrite formation. The responses in ANG II rats were prevented or ameliorated by ARB treatment. The results indicate that HS independently stimulates ROS formation, which may synergize with the effect of ANG II to limit peroxynitrite formation, leading to exacerbation of uAGT and greater injury during ANG II salt hypertension. renin-angiotensin system; reactive oxygen species; kidney injury; macrophage infiltration; dihydroethidium staining THE ENHANCEMENT OF INTRARENAL angiotensin II (ANG II) content contributing to hypertension and kidney damage is supported by the presence of all components of the renin-angiotensin system (RAS) in the kidney (27-29). During ANG II-dependent hypertension, intrarenal RAS activation is characterized by increased tissue levels of ANG II due to an augmented ANG II type 1 receptor (AT 1 R) binding with concomitant internalization of circulating ANG II (5, 40) and by de novo formation of ANG II (30). In response to chronic ANG II infusions, there are 1) enhancement of angiotensinogen (AGT) synthesis and secretion by...

Inhibition of nitric oxide (NO) synthesis by intrarenal administration of nitro-L-arginine (NLA) leads to decreases in urinary sodium excretion (UNaV) in association with the increases in renal vascular resistance (RVR). In the present study, we examined the ability of the kidney to alter its sodium excretion in response to acute changes in renal arterial pressure (RAP) in anesthetized dogs before and during intrarenal infusion of NLA (50 micrograms.kg-1.min-1). NO synthesis inhibition in 11 dogs increased RVR by 32 +/- 4% and decreased renal blood flow (RBF) by 25 +/- 3%, outer cortical blood flow by 25 +/- 6%, urine flow by 37 +/- 14%, UNaV by 71 +/- 5%, and fractional excretion of sodium (FENa) by 71 +/- 4%. Glomerular filtration rate was not significantly changed during NLA infusion. As previously reported, there was suppression of the RBF autoregulation plateau during NO synthesis inhibition. In addition, there was a marked attenuation of urine flow and UNaV responses to reductions in RAP (150 to 75 mmHg), with significant reductions in the slopes of the relationships between RAP vs. UNaV and RAP vs. FENa during NLA infusion. Similar responses were observed in nine other dogs treated with the angiotensin receptor antagonist losartan, indicating that an augmented activity of the renin-angiotensin system is not responsible for attenuation of the slope of the pressure-natriuresis relationship during NLA infusion. These data suggest that NO may participate in the mediation of the pressure-natriuresis response.