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...

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.

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