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 13,001 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An elevation in intracellular calcium ([Ca2+]i) in rats with chronic renal failure and elevated blood levels of PTH is associated with down-regulation of the mRNA of many proteins. Similarly, in phosphate depleted animals that have normal renal function and low blood levels of PTH, [Ca2+]i is elevated and the mRNA of PTH-PTHrP receptor is down-regulated. The effect of elevation in [Ca2+]i on molecular machinery of many proteins may represent a generalized phenomenon. Diabetes mellitus may also be associated with a rise in [Ca2+]i and therefore down-regulation of the mRNA of proteins may also occur. The present study examined the effect of streptozotocin-induced diabetes mellitus in rats on the [Ca2+]i of the renal proximal tubular cells and on their mRNAs of the PTH-PTHrP, V1a and AT1 receptors. The basal levels of [Ca2+]i of these cells increased significantly (P < 0.01) after one day of diabetes and remained elevated thereafter. There was a significant (r = 0.67, P < 0.01) direct correlation between the [Ca2+]i of the cells and blood levels of glucose up to 350 mg/dl, and the value of [Ca2+]i plateaued with higher concentrations of glucose. Three days of amlodipine therapy prevented and reversed the elevated levels of [Ca2+]i despite marked hyperglycemia. The mRNA of all three receptors in the kidney were down-regulated and this defect was prevented by amlodipine which normalized the [Ca2+]i of the cells. The results show that: (1) the hyperglycemia of IDDM in rats causes a significant elevation in the basal levels of [Ca2+]i of the renal proximal tubular cells and down-regulation of their mRNA of PTH-PTHrP, V1a and AT1 receptors; (2) normalization of the [Ca2+]i of these cells by treatment of the diabetic rats with amlodipine prevented the elevation of [Ca2+]i and the down-regulation of the mRNA of these receptors; (3) these effects occurred in the presence of normal renal function and normal blood of PTH and phosphorus.
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PMID:Elevation of [Ca2+]i of renal proximal tubular cells and down-regulation of mRNA of PTH-PTHrP, V1a and AT1 receptors in kidney of diabetic rats. 918 88

The role of angiotensin II (ANG II) in colonic secretion of K+ was examined in rats with chronic renal failure (CRF). The basal net secretory flux of 86Rb+ (as a tracer for K+) across the CRF distal colon (-0.20 +/- 0.04 mu eq.cm-2.h-1) was reversed to an absorptive flux (0.35 +/- 0.05 mu eq.cm-2.h-1) by injecting the rats with the AT1 receptor antagonist, losartan. A similar result was observed when losartan was added to the CRF colonic tissue in vitro. In contrast, an AT2 receptor antagonist, PD-123319, did not reverse the CRF-induced alterations in Rb+ transport across the short-circuited colonic tissue. Plasma concentrations of ANG II, aldosterone, and K+, as well as the ANG II content of colonic tissues from CRF and normal rats, were similar. However, specific 125I-labeled ANG II binding sites in rat distal colon increased twofold in CRF [maximal specific binding (Bmax) = 28.6 +/- 1.6 fmol/mg protein] compared with normal (Bmax = 15.2 +/- 0.4 fmol/mg protein). These studies suggest that CRF-induced secretion of K+ by the colon is mediated by an upregulation of AT1 receptors present in CRF.
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PMID:Local upregulation of colonic angiotensin II receptors enhances potassium excretion in chronic renal failure. 948 22

Glomerulosclerosis and tubulointerstitial fibrosis are common morphological correlates of many end-stage kidneys. There is ample evidence that transforming growth factor-beta (TGF-beta) plays a major role in these alterations by directly stimulating synthesis of many extracellular matrix components and reducing collagenase production, finally leading to renal scarring. Although many factors may induce TGF-beta expression in the kidney, one very interesting aspect is the link between angiotensin II (ANG II) and TGF-beta. Originating from observations in vascular smooth muscle cells, there are now several additional studies showing that ANG II stimulates TGF-beta expression in the kidney. Although cell culture studies have convincingly demonstrated that the vasoactive peptide directly stimulates transcription as well as bioactivation of TGF-beta, the in vivo evidence is more indirect. Nevertheless, there are several pathophysiological situations including unilateral ureteral obstruction, chronic cyclosporin A nephrotoxicity, various models of hypertension, and probably diabetic nephropathy in which ANG II-mediated TGF-beta induction has been demonstrated to play an important role in the progression of the disease. The fascinating aspect of this relationship between ANG II and TGF-beta is the fact that hemodynamic changes as well as structural changes are linked together generating a unifying model of progression of chronic renal failure with ANG II as the key player. Angiotensin-converting enzyme (ACE) inhibitor and the more recently introduced AT1-receptor blocker may be potential drugs to interfere with this ANG II-mediated TGF-beta expression. Therefore, these drugs should not only be considered as antihypertensive medications, but should rather be viewed as renoprotective substances influencing renal remodeling by preventing local TGF-beta expression.
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PMID:Link between angiotensin II and TGF-beta in the kidney. 952 2

Blockade of the renin-angiotensin system with angiotensin-converting enzyme (ACE) inhibitors is now recognized as an effective approach for the treatment of hypertension and congestive heart failure. In addition, ACE inhibitors are very effective for the prevention of chronic renal failure. Today, it is possible to antagonize the effects of angiotensin II more specifically using AT1 receptor antagonists. Several non-peptide, orally active angiotensin II receptor antagonists have recently been developed clinically. These new molecules are as effective as ACE inhibitors, calcium antagonists and beta-blockers at reducing blood pressure in hypertensive patients. Furthermore, they appear to have similar systemic and renal hemodynamic properties in patients with congestive heart failure and renal diseases. Now, several large clinical trials such as the LIFE, the RENAAL and the ELITE II studies are under way to investigate the long-term benefits of one of these compounds in hypertension, heart failure and type II diabetic nephropathy.
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PMID:[Angiotensin II AT1 receptor antagonists: clinical development and future perspectives]. 977 27

At the present time we cannot assume that the proven benefits of ACEI on renal disease will be reproduced by using AT1-ra. With potentially differing modes of activity of these drugs, they cannot be seen as interchangeable and ACEI should remain the drug of choice in patients with progressive renal disease unless they are not tolerated. It is possible that AT1-ra may offer additional advantages in some patients or that synergy exists between the two agents, but this view will remain entirely speculative unless proper trials are conducted. Despite the results of the ELITE study [22], the uncertainty regarding the use AT1-ra in cardiovascular disease mirrors that of renal disease. This issue is obviously of relevance to the nephrologist in view of the spectrum of cardiac disease that accompanies chronic renal failure, such as left ventricular hypertrophy and cardiac failure, which provide multiple indications for manipulation of RAS. Despite their renoprotective effect, previous studies on ACEI [3,4] have not shown an overall reduction in mortality and this issue needs to be addressed in addition to renoprotection in studies comparing AT1-ra and ACEI.
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PMID:Angiotensin converting enzyme inhibitors and angiotensin receptor (AT1) antagonists: either or both for primary renal disease? 1005 68

Chronic renal failure is associated with disturbances in nitric oxide (NO) production. This study was conducted to determine the effect of 5/6 nephrectomy (5/6 Nx) on expression of intrarenal neuronal nitric oxide synthase (nNOS) in the rat. In normal rat kidney, nNOS protein was detected in the macula densa and in the cytoplasm and nuclei of cells of the inner medullary collecting duct by both immunofluorescence and electron microscopy. Western blot analysis revealed that 2 wk after 5/6 Nx, there were significant decreases in nNOS protein expression in renal cortex (sham: 95.42+/-15.60 versus 5/6 Nx: 47.55+/-12.78 arbitrary units, P<0.05, n = 4) and inner medulla (sham: 147.70+/-26.96 versus 5/6 Nx: 36.95+/-17.24 arbitrary units, P<0.005, n = 8). Losartan treatment was used to determine the role of angiotensin II (AngII) AT1 receptors in the inhibition of nNOS expression in 5/6 Nx. Losartan had no effect on the decreased expression of nNOS in the inner medulla, but partially increased nNOS protein expression in the cortex of 5/6 Nx rats. In contrast, in sham rats losartan significantly inhibited nNOS protein expression in the cortex (0.66+/-0.04-fold of sham values, P<0.05, n = 6) and inner medulla (0.74+/-0.12-fold of sham values, P<0.05, n = 6). nNOS mRNA was significantly decreased in cortex and inner medulla from 5/6 Nx rats, and the effects of losartan on nNOS mRNA paralleled those observed on nNOS protein expression. These data indicate that 5/6 Nx downregulates intrarenal nNOS mRNA and protein expression. In normal rats, AngII AT1 receptors exert a tonic stimulatory effect on expression of intrarenal nNOS. These findings suggest that the reduction in intrarenal nNOS expression in 5/6 Nx may play a role in contributing to hypertension and altered tubular transport responses in chronic renal failure.
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PMID:Downregulation of neuronal nitric oxide synthase in the rat remnant kidney. 1020 53

Electrolytes and water are bidirectionally transported across the epithelial cells of mammalian small and large intestines. In animals with chronic renal failure, plasma levels of angiotensin II and specific 125I-angiotensin II binding sites increase and result in enhanced excretions of K+, Cl- and urate from distal colon, in an AT1-receptor sensitive manner. Angiotensin-converting enzyme activity and mRNA levels for renin-2 and AT1A-receptor are blunted or lowered transiently by gastric intake of low Na+ in rodent, suggesting that angiotensin II serves as a humoral mediator for "gastric Na+ monitor". Angiotensin II causes also very potent contractions of gastrointestinal smooth muscles as shown in vascular smooth muscles. This review is focused on understanding potential roles of angiotensin II in gastrointestinal functions.
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PMID:[Modulations by stimulation of angiotensin II type 1 receptor of gastrointestinal functions]. 1036 34

The role of the AT1 receptor in stimulating colonic K+ secretion was investigated in rats with chronic renal failure (CRF) induced by 5/6 nephrectomy. Compared to control rats, CRF rats up-regulate mucosal AT1 receptors approximately two-fold in the proximal (PC) and distal (DC) colonic segments. In contrast, there was no alteration in AT1 receptor protein mass in jejunal or ileal mucosa. Using 86Rb+ as a tracer for transmural K+ fluxes, a significant stimulation of the basal K+ secretory flux across both PC and DC was observed in vitro and this alteration in K+ transport was temporally correlated with the increase in angiotensin II (ANG II) receptors. In both PC and DC the significant increases in the receptor protein were evident 48 h after partial nephrectomy and they were sustained through 6 weeks. These studies support the hypothesis that CRF-induced secretion of K+ is mediated by an up-regulation of AT1 receptors exclusively in the large intestinal segments.
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PMID:AT1 receptor up-regulation in intestine in chronic renal failure is segment specific. 1037 66

A lot of evidence points to the important role of the renin-angiotensin system in the physiopathology of hypertension and the progression of chronic renal failure. In this review, the authors report the data concerning the protective effects of antagonists of angiotensin II AT1 receptors (AT1ra). The AT1 ra have been shown to have beneficial effects in most experimental models of nephropathy in which they have been tested (renal ischaemia, essential or induced hypertension, glomerulonephritis, 5/6 nephrectomy, renal transplantation, induced diabetes, toxic and radiotherapy-induced nephropathy). Clinical trials confirm these beneficial effects. In healthy subjects and hypertensive patients, the AT1 ra have identical effects to those of angiotensin converting enzyme (ACE) inhibitors on renal haemodynamics. In hypertensives, Candesartan and Irbesartan increase renal blood flow and the glomerular filtration rate and decrease the filtration fraction. Two studies have also shown that Candesartan and Irbesartan reduce proteinuria in diabetic patients. Similar results have been reported in essential hypertension with renal failure. These data suggest that AT1 ra have beneficial effects on the progression of experimental kidney disease and on proteinuria in the clinical setting. Of the pharmacological agents available for use in this class, it is essential to propose molecules whose efficacy in antagonising the effects of angiotensin II lasts throughout the 24 hour period. Clinical trials are under way to evaluate the effects of AT1 ra on renal function in man over a long period.
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PMID:[Are the antagonists of angiotensin II AT1 receptors protectors of the kidney?]. 1044 11

Enteric excretion of oxalate was studied in rats with chronic renal failure (CRF) by measuring the magnitude and direction of oxalate fluxes in vitro across short-circuited preparations of distal colon in Ussing chambers. The net absorptive flux of oxalate that is characteristic of colonic tissues removed from control rats was significantly changed to a net secretory flux in CRF rats. Injecting CRF rats with a specific angiotensin II (AngII) receptor (AT1) antagonist, losartan, results in a reversal of the CRF-induced net secretory flux (-13.87+/-0.08 pmol x cm(-2) x h(-1)) to an absorptive flux (+7.32+/-3.68 pmol x cm(-2) x h(-1)) by normalizing the unidirectional fluxes of oxalate. Similarly, oxalate fluxes were normalized across CRF colonic tissues by acute, in vitro application of losartan to the serosal bathing solution. It was also possible to simulate the CRF-induced secretory flux of oxalate (Jsm) in vitro across colonic tissues removed from control rats. Serosal application of AngII at 10(-6), 10(-5), and 10(-4) M resulted in significant increases in the s-->m flux of oxalate (increasing deltaJsm = 4.06+/-1.2, 8.41+/-0.94, and 13.8+/-3.8 pmol x cm(-2) x h(-1), respectively). Taken together, these results suggest that CRF-induced oxalate secretion is at least partly mediated by AngII, which is consistent with previous findings of a twofold upregulation of AT1 receptors in CRF colonic mucosa.
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PMID:Regulatory aspects of oxalate secretion in enteric oxalate elimination. 1054 Dec 56


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