Abstract-Distal nephron renin may provide a possible pathway for angiotensin (Ang) I generation from proximally delivered angiotensinogen. To examine the effects of Ang II on distal nephron renin, we compared renin protein and mRNA expression in control and Ang II-infused rats. Kidneys from sham (nϭ9) and Ang II-infused (80 ng/kg per minute, 13 days, nϭ10) Sprague-Dawley rats were processed by immunohistochemistry, Western blot, reverse transcriptase-polymerase chain reaction (RT-PCR), and quantitative real-time RT-PCR. Ang II infusion increased systolic blood pressure (181Ϯ4 versus 115Ϯ5 mm Hg) and suppressed plasma and kidney cortex renin activity. Renin immunoreactivity was suppressed in juxtaglomerular apparatus (JGA) cells in Ang II-infused rats compared with sham (0.1Ϯ0.1 versus 1.0Ϯ0.1 relative ratio) but increased in distal nephron segments (6.4Ϯ1.4 versus 1.0Ϯ0.1 cortex; 2.5Ϯ0.3 versus 1.0Ϯ0.2 medulla). Tubular renin immunostaining was apically distributed in principal cells colocalizing with aquaporin-2 in connecting tubules and cortical and medullary collecting ducts. Renin protein levels were decreased in the kidney cortex of Ang II-infused rats compared with that of sham (0.4Ϯ0.2 versus 1.0Ϯ0.4) rats but higher in the kidney medulla (1.2Ϯ0.4 versus 1.0Ϯ0.1). In kidney medulla, RT-PCR and quantitative real-time PCR showed similar levels of renin transcript in both groups. In summary, the detection of renin mRNA in the renal medulla, which is devoid of JGA, indicates local synthesis rather than an uptake of JGA renin. In contrast to the inhibitory effect of Ang II on JGA renin, Ang II infusion stimulates renin protein expression in collecting ducts and maintains renin transcriptional levels in the medulla, which may contribute to the increased intrarenal Ang II levels in Ang II-dependent hypertension. Key Words: renin Ⅲ angiotensin II Ⅲ angiotensinogen Ⅲ immunohistochemistry Ⅲ Western blot R enin is synthesized primarily by the juxtaglomerular apparatus (JGA). 1 However, renin mRNA and protein have been detected in proximal, connecting tubule and collecting duct cells of human and mouse kidneys as well as in extrarenal tissues. [2][3][4][5][6][7] Although regulation of renin synthesis and secretion from JGA cells has been extensively studied, 1,8 -13 very little is known about the regulation of tubular renin. 7,14 -16 Renin formation in tubular segments may have greater importance than previously thought in view of evidence of high concentrations of angiotensinogen (AGT), as well as angiotensin (Ang) I and Ang II in proximal tubule fluid, 17,18 and in view of the enhancement of renal AGT mRNA and protein levels in Ang II-dependent hypertension. 19,20 Recent studies in Ang II-infused hypertensive rats have shown that there is an increased urinary excretion of AGT, 21 which is closely correlated with intrarenal Ang II content. 21 Enhancement of urinary AGT excretion suggests increased distal nephron AGT delivery and subsequent Ang I and Ang II formation as long as there is availability of an adequate...

Abstract-Angiotensin (Ang) II-infused hypertensive rats exhibit increases in renal angiotensinogen mRNA and protein, as well as urinary angiotensinogen excretion in association with increased intrarenal Ang II content. The present study was performed to determine if the augmentation of intrarenal angiotensinogen requires activation of Ang II type 1 (AT 1 ) receptors. Male Sprague-Dawley rats (200 to 220 g) were divided into 3 groups: sham surgery (nϭ10), subcutaneous infusion of Ang II (80 ng/min, nϭ11), and Ang II infusion plus AT 1 blocker (ARB), olmesartan (5 mg/d, nϭ12). Ang II infusion progressively increased systolic blood pressure (SBP) compared with sham (178Ϯ8 mm Hg versus119Ϯ4 at day 11). ARB treatment prevented hypertension (113Ϯ6 at day 11). Twenty-four-hour urine collections were taken at day 12, and plasma and tissue samples were harvested at day 13. The Ang IIϩARB group had a significant increase in plasma Ang II compared with Ang II and sham groups (365Ϯ46 fmol/mL versus 76Ϯ9 and 45Ϯ14, respectively). Nevertheless, ARB treatment markedly limited the enhancement of kidney Ang II by Ang II infusion (65Ϯ17 fmol/g in sham, 606Ϯ147 in Ang II group, and 288Ϯ28 in Ang IIϩARB group). Ang II infusion significantly increased kidney angiotensinogen compared with sham (1.69Ϯ0.21 densitometric units versus 1.00Ϯ0.17). This change was reflected by increased angiotensinogen immunostaining in proximal tubules. ARB treatment prevented this increase (1.14Ϯ0.12). Urinary angiotensinogen excretion rates were enhanced 4.7ϫ in Ang II group (4.67Ϯ0.41 densitometric units versus 1.00Ϯ0.21) but ARB treatment prevented the augmentation of urinary angiotensinogen (0.96Ϯ0.23). These data demonstrate that augmentation of intrarenal angiotensinogen in Ang II-infused rats is AT 1 -dependent and provide further evidence that urinary angiotensinogen is closely linked to intrarenal Ang II in Ang II-dependent hypertension. Key Words: angiotensin II Ⅲ angiotensinogen Ⅲ receptors, angiotensin II Ⅲ rats Ⅲ kidney A ngiotensin II (Ang II) plays an important role in proximal tubular reabsorptive function primarily via activation of Ang II type 1 (AT 1 ) receptor at both basolateral and luminal membranes. 1 Although some Ang II type 2 receptors have been confirmed on proximal tubules, 2 most functional studies suggest that the major effects of Ang II on proximal tubules are via AT 1 receptors. 3 Several studies have suggested that Ang II also plays an important role in the regulation of distal tubular reabsorption rate. 4 This effect was blocked by either saralasin or losartan, indicating that this stimulation involves AT 1 receptor activation. 4 These findings, together with the demonstration that AT 1 receptor is present on the luminal membranes of distal nephron segments, 5,6 suggest that luminal Ang II plays an important role in the regulation not only of proximal reabsorption rate but also of distal tubular reabsorptive function. 7 Studies in isolated proximal tubular cells showed that Ang II stimulates Na ϩ /H ϩ exchanger via AT 1 ...

Abstract-Renin in collecting duct cells is upregulated in chronic angiotensin II-infused rats via angiotensin II type 1 receptors. To determine whether stimulation of collecting duct renin is a blood pressure-dependent effect; changes in collecting duct renin and associated parameters were assessed in both kidneys of 2-kidney, 1-clip Goldblatt hypertensive (2K1C) rats. Renal medullary tissues were used to avoid the contribution of renin from juxtaglomerular cells. Systolic blood pressure increased to 184Ϯ9 mm Hg in 2K1C rats (nϭ19) compared with sham rats (121Ϯ6 mm Hg; nϭ12 T he renin-angiotensin system regulates blood pressure, renal hemodynamics, and tubular sodium reabsorption. During angiotensin II (Ang II)-dependent hypertension, there is an augmentation of intrarenal Ang II levels that is greater than can be explained on the basis of the plasma Ang II concentrations. 1-4 Increased Ang II kidney content results from the combination of uptake of circulating Ang II and local formation of Ang II from enhanced angiotensinogen (AGT) produced and secreted by proximal tubule cells. 2,5,6 Chronic Ang II infusion stimulates proximal tubule AGT production and tubular secretion leading to increased urinary AGT excretion, indicating that the secreted AGT traverses the distal nephron segments. 6,7 In addition to juxtaglomerular (JG) cells, renin is expressed in the principal cells of connecting tubules and cortical and medullary collecting ducts, suggesting angiotensin peptide formation in the distal nephron segments. 8 -10 The upregulation of renin in the collecting ducts (CDs) of Ang II-infused hypertensive rats, along with substantial angiotensinconverting enzyme activity in the late distal tubular fluid and in urine, 11 further support the hypothesis that, in Ang IIdependent hypertension, there is an increased spillover of proximally produced AGT into distal nephron segments leading to augmented Ang II formation and enhanced distal Na ϩ reabsorption. 12,13 In Ang II-infused rats, JG and CD renin are differentially regulated. 13 Treatment with Ang II type 1 (AT 1 ) receptor blockers prevents the stimulation of distal nephron renin mRNA and protein in Ang II-infused rats, 13 a response opposite from the well-known effect of AT 1 receptor blockade on JG renin. Because AT 1 receptor blocker treatment of Ang II-infused rats also prevents the Ang II-mediated increases in arterial blood pressure, an alternative possibility is that the restoration of normal arterial blood pressure was responsible for the reduced responses in CD renin. The present study was performed to elucidate whether the stimu-