Genetically conditioned interaction among microRNA-155, alpha-klotho, and intra-renal RAS in male rats: Link to CKD progression.

Incident chronic kidney disease (CKD) varies in populations with hypertension of similar severity. Proteinuria promotes CKD progression in part due to activation of plasminogen to plasmin in the podocytes, resulting in oxidative stress-mediated injury. Additional mechanisms include deficiency of renal alpha-klotho, that inhibits Wnt/beta-catenin, an up regulator of intra-renal renin angiotensin system (RAS) genes. Alpha-klotho deficiency therefore results in upregulation of the intra-renal RAS via Wnt/beta-catenin. In hypertensive, Dahl salt sensitive (DS) and spontaneously hypertensive rats (SHR), we investigated renal and vascular injury, miR-155, AT1R, alpha-klotho, and TNF-α. Hypertensive high salt DS (DS-HS), but not SHR developed proteinuria, plasminuria, and glomerulosclerosis. Compared to DS low salt (DS-LS), in hypertensive DS-HS alpha-klotho decreased 5-fold in serum and 2.6-fold in kidney, whereas serum mir-155 decreased 3.3-fold and AT1R increased 52% in kidney and 77% in aorta. AT1R, alpha-klotho, and miR-155 remained unchanged in prehypertensive and hypertensive SHR. TNF-α increased by 3-fold in serum and urine of DS-HS rats. These studies unveiled in salt sensitive DS-HS, but not in SHR, a genetically conditioned dysfunction of the intermolecular network integrated by alpha-klotho, RAS, miR-155, and TNF-α that is at the helm of their end-organ susceptibility while plasminuria may participate as a second hit.

Endogenously synthesized nitric oxide prevents endotoxin-induced glomerular thrombosis.

Escherichia coli endotoxin (LPS) can induce the clinical syndrome of septic shock and renal cortical necrosis and can stimulate nitric oxide (NO) production from macrophages, vascular smooth muscle, and glomerular mesangial cells in vitro. NO is an endogenous vasodilator, which also inhibits platelet aggregation and adhesion. We therefore sought to determine whether LPS would stimulate NO production in vivo and, if so, whether this NO would modulate endotoxin-induced glomerular thrombosis. The stable NO end-products, NO2 and NO3, were measured in serum and urine collections from rats during baseline and after injection of LPS, with or without substances that modulate NO synthesis. The urinary excretion of NO2/NO3 was 1,964 +/- 311 nm/8 h during the baseline and increased to 6,833 +/- 776 nm/8 h after a single intraperitoneal injection of 0.1 mg/kg LPS (P < 0.05). The serum concentration of NO2/NO3 also significantly increased after LPS injection. Both the urine and serum stimulation was significantly prevented by the NO synthesis inhibitor, Nw-nitro-L-arginine methyl ester (L-NAME). L-Arginine, given with LPS+L-NAME significantly restored the NO2/NO3 levels in the urine. Ex vivo incubation of tissues from rats treated with LPS demonstrated NO production by the aorta, whole kidney, and glomeruli, but not cortical tubules. Histological examination of kidneys from rats given either LPS or L-NAME alone revealed that 2 and 4.5% of the glomeruli contained capillary thrombosis, respectively. In contrast, rats given LPS+L-NAME developed thrombosis in 55% of glomeruli (P < 0.001), which was significantly prevented when L-arginine was given concomitantly. We conclude that LPS stimulates endogenous production of NO in vivo and that this NO is critical in preventing LPS-induced renal thrombosis.

Mesangial function in ureteral obstruction in the rat. Blockade of the efferent limb.

The kinetics for mesangial uptake and transport of radiolabeled aggregated human immunoglobulin (Ig)G (AHIgG(125)I) deviated markedly from normal in male Sprague-Dawley rats with ureteral obstruction. Four experimental groups, each containing 25 rats, were used: (a) bilateral ureteral ligation (BUL) with release of one ureter 24 h later; (b) unilateral ureteral ligation with release 24 h later [UUL(R)]; (c) unilateral ureteral ligation without release (unreleased) [UUL(U)]; (d) uremia-control, which consisted of rats with ligated left ureter and a severed right ureter. A similar number of sham-operated rats served as control for each group. AHIgG(125)I (45 mg/100 g body wt) was given intravenously 1 h after release of the ureteral obstruction (25 h after ureteral obstruction or sham surgery). Groups of five control and five experimental animals were sacrificed at 2, 4, 8, 16, and 24 h after injection. At all time intervals, concentrations of AHIgG(125)I in isolated glomeruli from control animals were similar to values obtained from nonobstructed kidneys of UUL(U) and UUL(R) rats: a linear decrease in concentration over a period of 24 h was observed when the logarithm of glomerular AHIgG(125)I concentration was plotted against time. Aberrations in the kinetics were apparent in obstructed kidneys but not in liver, spleen, or blood concentrations of AHIgG(125)I: (a) At 2 h in all obstructed kidneys, glomerular concentration of AHIgG(125)I was markedly reduced. (b) In BUL (released or unreleased), glomerular concentrations of AHIgG(125)I from 4 to 16 h were congruent with 10-fold those in UUL(U) or UUL(R) kidneys. (c) The significant decline in glomerular concentration between 4 and 16 h in control and nonobstructed kidneys was not observed in UUL(R), UUL(U), or BUL (released or unreleased) kidneys; in all obstructed kidneys, a plateau in glomerular concentrations of AHIgG(125)I was observed between 4 and 16 h. (d) After 16 h at a time when the blood level of AHIgG(125)I had decreased to 3% of initial values, there was progressive fall in glomerular AHIgG(125)I. Similar results were obtained in the uremia-control group in rats, which indicated that uremia per se had no measurable effect on mesangial kinetics. These studies demonstrate that ureteral occlusion induces alterations in mesangial uptake (afferent limb) and egress (efferent limb) of macromolecules. Particularly evident is the "blockade" of the efferent limb which is demonstrable at high blood levels of AHIgG(125)I. These alterations in the transit of macromolecules through the mesangium may be mediated in part by the hemodynamic changes that accompany ureteral obstruction.

Increased nitric oxide synthase activity despite lack of response to endothelium-dependent vasodilators in postischemic acute renal failure in rats.

Lack of response to endothelium-dependent vasodilators generally has been considered to be evidence for decreased nitric oxide synthase (NOS) activity and NO generation after ischemic or hypoxic injury to vital organs including the kidney. In this study, renal blood flow (RBF) responses to endothelium-dependent vasodilators acetylcholine and bradykinin and the endothelium-independent vasodilator prostacyclin, the nonselective NOS inhibitor L-NAME (without and with L-arginine), the inducible NOS inhibitor aminoguanidine, and the NO-donor sodium nitroprusside were examined in 1-wk norepinephrine-induced (NE) and sham-induced acute renal failure (ARF) rats. Compared with sham-ARF, there was no increase in RBF to intrarenal acetylcholine and bradykinin, but a comparable RBF increase to prostacyclin in NE-ARF kidneys. However, there was a significantly greater decline in RBF to intravenous L-NAME in NE- than sham-ARF rats (-65 +/- 8 vs. -37 +/- 5%, P < 0.001) which was completely blocked by prior L-arginine infusion. There was no change in RBF to the inducible NOS specific inhibitor aminoguanidine. Unlike sham-ARF, there was no increase in RBF to intrarenal sodium nitroprusside in NE-ARF. Immunohistochemistry and immunofluorescence detection of constitutive (c) NOS using mouse monoclonal antibody were carried out to positively determine the presence of cNOS in NE-ARF. 90% of renal resistance vessels showed evidence of endothelial cNOS in both sham- and NE-ARF. Taken together, results of these experiments are consistent with the conclusion that NOS/NO activity is, in fact, maximal at baseline in 1-wk NE-ARF and cannot be increased further by exogenous stimuli of NOS activity. The increased NOS is likely of the constitutive form and of endothelial origin. It is suggested that the increased NOS activity is in response to ischemia-induced renal vasoconstrictor activity. Attenuated response to endothelium-dependent vasodilators cannot be interpreted only as evidence for decreased NOS activity.

Angiotensin-converting enzyme inhibition and renal protection. An assessment of implications for therapy.

The role of hypertension in the pathogenesis of renal damage is a subject of both historical interest and current investigation. Because of the difficulty associated with studying the pathophysiologic role of glomerular injury in systemic hypertension, experimental models have provided much of the data in this field. The mechanisms leading to glomerular injury are complex and not fully elucidated. Mesangial and endothelial cell injury are thought to be important pathophysiologic mechanisms in the renal injury associated with hypertension. One hypothesis suggests that glomerular hypertension (ie, a hemodynamic event) is the primary pathogenetic mechanism, but another supports the notion that glomerular hypertrophy (ie, abnormal growth-related events) contributes to injury. The intrarenal renin-angiotensin system may play an important pathogenetic role in end-stage renal disease. Angiotensin-converting enzyme (ACE) inhibition has been shown to arrest the progression of renal injury in animal models. Although the clinical database is incomplete, the findings of anecdotal reports and short-term studies suggest that ACE inhibition may preserve renal function in patients with scleroderma renal crisis, reduce proteinuria in patients with diabetic nephropathy, and normalize renal hemodynamics in patients with a variety of renal diseases. The beneficial effects of ACE inhibition may be due to both hemodynamic (eg, reduction in glomerular capillary and intraglomerular pressures) and nonhemodynamic (eg, potassium-sparing and reduction in mesangial proliferation) mechanisms. The precise role of ACE inhibitors in the prevention of renal damage awaits the results of ongoing long-term, double-blind clinical studies. Nevertheless, ACE inhibition may be an appropriate therapeutic alternative in the hypertensive patient whose renal injury is progressing despite aggressive antihypertensive therapy.

Severe hypokalemia induced by hemodialysis.

During dialysis, it is assumed that the serum electrolyte levels asymptotically approach the concentration in the dialysate. In five patients, we observed an average 20% fall in serum potassium level, although the dialysate contained 42% more potassium than the predialysis serum. One patient had quadriplegia and near respiratory arrest as a complication of hypokalemia. The cause of the hypokalemia was a rapid shift of potassium from the extracellular to the intracellular space secondary to correction of acidosis. All patients entered dialysis with a history suggesting prolonged potassium loss, marked acidosis, and moderate hypokalemia; thus, the dialysate potassium concentration should be higher than normal, and frequent determinations of the serum potassium level should be performed. Therapy resulting in rapid correction of acidosis in uremic patients undergoing hemodialysis may cause large transcompartmental shifts of potassium. Potassium transfer across the dialysis membrane may be inadequate to compensate for such shifts, and life-threatening hypokalemia may occur.

Recurrence of idiopathic membranous nephropathy in a renal allograft.

A middle-aged man with idiopathic membranous nephropathy, who developed chronic renal failure, received a cadaver renal allograft. Two months later, massive, persistent proteinuria developed. A biopsy specimen of the allograft showed changes characteristic of membranous nephropathy and identical to those present in the patient's own kidney. The criteria for recurrence of glomerulonephritis in renal allografts are met in this case.

Nitric oxide in hypertension: relationship with renal injury and left ventricular hypertrophy.

Hypertension is accompanied by architectural changes in the kidney, heart, and vessels that are often maladaptive and can eventually contribute to end-organ disease such as renal failure, heart failure, and coronary disease. Nitric oxide, an endogenous vasodilator and antithrombotic agent synthesized in the endothelium by a constitutive nitric oxide synthase, inhibits growth-related responses to injury in vascular cells. Specifically, in the presence of hypertension, nitric oxide may work in the kidney by inhibiting both mesangial cell hypertrophy and hyperplasia as well as synthesis of extracellular matrix and in the heart and systemic vessels by modulating smooth muscle cell hypertrophy and hyperplasia. The effects of nitric oxide are antagonistic of the effects of angiotensin II. Shear stress and cyclic strain, physical forces known to operate in hypertension, are accompanied by increases in endothelial nitric oxide synthase expression, nitric oxide synthase protein, and nitric oxide synthase activity in endothelial cells. Experimental studies using genetic models of hypertension show a variation in hypertension-modulated vascular nitric oxide synthase activity in different strains of rats. These studies suggest that upregulation of vascular nitric oxide synthase activity is a homeostatic adaptation to increased hemodynamic workload in hypertension and that this may help prevent end-organ damage. If these findings apply to humans, differences in end-organ disease seen in patients with similar degrees of hypertension may be due in part to genetic differences in vascular nitric oxide synthase activity in response to hypertension.

The link among nitric oxide synthase activity, endothelial function, and aortic and ventricular hypertrophy in hypertension.

The adaptive changes that occur in the left ventricle (LV) and vessels in response to hypertension, namely, muscle hypertrophy/hyperplasia, endothelial dysfunction, and extracellular matrix increase, do not depend solely on blood pressure elevation. These changes are in fact, maladaptive since they are forerunners of cardiac failure, stroke, and renal failure. Nitric oxide, an endogenous vasodilator and inhibitor of vascular smooth muscle cell growth, is synthesized in the endothelium by constitutive nitric oxide synthase (cNOS). We investigated the relationships among LV and aortic cNOS activity (conversion of [14C] L-arginine to [14C] L-citrulline), with LV hypertrophy (LV weight/body weight), and (2) aortic hypertrophy (aortic weight/ length) in spontaneously hypertensive rats (SHR) and Dahl salt-sensitive (DS) rats matched for blood pressure (219 +/- 12 versus 211 +/- 7 mm Hg, P = NS) and age. Compared with their normotensive counterparts, aortic cNOS activity was increased 106% in SHR but reduced by 73% in DS rats. The correlation between blood pressure and aortic cNOS activity was positive (r = .74, P < .01) in SHR and negative (r = -.82, P < .01) in DS rats, LV cNOS activity was increased 73% in SHR compared with normotensive Wistar-Kyoto rats (P < .01). On the other hand, LV cNOS activity was not increased in hypertensive DS rats compared with normotensive DS rats. In SHR, aortic hypertrophy did not increase significantly and LV hypertrophy increased only 15%, whereas in hypertensive DS rats the aorta and LV hypertrophied 36% and 88%, respectively (both P < .01). Moreover, in DS rats there was a negative correlation between cNOS activity and aortic hypertrophy (r = -.70, P < .01). In DS rats, antihypertensive therapy consisting of an angiotensin-converting enzyme inhibitor, perindopril, and a diuretic, indapamide, normalized blood pressure, aortic cNOS activity, and LV hypertrophy and reduced aortic hypertrophy. Our studies imply that upregulation of vascular cNOS activity has a protective cardiovascular homeostatic role in hypertension. Clinically, the variable end-organ disease observed in individuals with similar severity of hypertension may be explained, at least in part, by genetically conditioned differences in vascular cNOS activity in response to hypertension.

Nitric oxide synthase activity and renal injury in genetic hypertension.

Nitric oxide (NO) is an endogenous vasodilator synthesized in the endothelium by constitutive NO synthase (cNOS). We have shown that upregulation of cNOS activity in hypertension may contribute to forestalling left ventricular and aortic hypertrophy (Hypertension. 29: 235, 1997). NO has been shown to inhibit growth-related responses affecting vascular smooth muscle, and mesangial cells, as well as reduce production of extracellular matrix in response to injury. Here, we investigated the relationship between renal cNOS activity (conversion of [14C] L-arginine to [14C] L-citrulline) and glomerular (GIS) and tubulointerstitial (TIS) injury scores and urinary protein excretion, indices of renal injury, in age and blood pressure matched spontaneously hypertensive rats (SHR, SBP 220+/-9 mm Hg) fed 0.5% NaCl diet and Dahl salt-sensitive (DS) rats fed 4% NaCl diet (DS-4%, SBP 228+/-8 mm Hg) as well as their normotensive counterparts Wistar Kyoto rats fed 0.5% NaCl diet (WKY, 137+/-3 mm Hg) and DS rats fed 0.5% NaCl diet (DS-0.5%, SBP 135+/-4 mm Hg). In SHR, renal medullary cNOS activity was 89% higher than in WKY (8.91+/-0.98 vs 4.71+/-0.37 nmol/min/g protein, P<0.05) whereas, in hypertensive DS-4% rats cNOS activity was 43% lower than in DS-0.5% rats (1.98+/-0.16 vs 3.48+/-0.29 nmol/min/g protein, P<0.05). Renal cortical cNOS was lower than in medulla but similar in all groups; inducible NOS activity was not detected. Despite hypertension of similar severity and duration, hypertensive DS-4% developed 9 fold more GIS (190+/-42 vs 21+/-11), 20 fold more TIS (4.0+/-0.7 vs 0.2+/-0.3), and 5 fold more proteinuria (54+/-11 vs 8.5+/-3.0 mg/day), all P<0.05. The current studies, in conjunction with our recent studies in heart and aorta, strongly suggest that in hypertension, increased cNOS activity may provide a protective homeostatic role in all the end-organs that are targets of hypertensive injury.

Inhibition of human mesangial cell proliferation by calcium channel blockers.

Human mesangial cells in culture proliferate in response to platelet-derived growth factor (PDGF) and thrombin. Both of these agents also induce changes in cytosolic calcium that are dependent on both mobilization of intracellular calcium and influx of extracellular calcium. We hypothesized that calcium channel blockers, by preventing influx of extracellular calcium, may inhibit proliferation induced by these mitogens. We found that three different calcium channel blockers, diltiazem, nifedipine, and verapamil, were able to significantly inhibit [3H]thymidine incorporation into human mesangial cells induced by either PDGF or thrombin. The inhibitory effect of these agents was significant at 10(-5) M. The calcium channel blockers also attenuated the increases in cell number and percentage of labeled nuclei induced by these mitogens. In contrast, dantrolene, an inhibitor of intracellular calcium mobilization, had no significant effect on [3H]thymidine incorporation by PDGF or thrombin. Finally, the calcium channel agonist, Bay K 8644 was found to stimulate [3H]thymidine incorporation into mesangial cells. Although the mechanisms for these effects of calcium channel blockers are not proven, these studies suggest that influx of extracellular calcium is an important signal in mitogen-induced mesangial proliferation and that these agents can be beneficial in preventing or attenuating renal diseases characterized by proliferation of these cells.

Effects of amino acid infusion on renal hemodynamics. Role of endothelium-derived relaxing factor.

Ingestion of protein or intravenous infusion of amino acids acutely elevates glomerular filtration rate (GFR) and renal plasma flow (RPF) by unknown mechanisms. Endothelium-derived relaxing factor (EDRF), now known to be nitric oxide derived from metabolism of L-arginine, participates in local regulation of vascular tone. To investigate the hypothesis that EDRF may participate in the renal vasodilatation and increased GFR after amino acid infusion, we characterized the effect of inhibition of EDRF synthesis with NG-monomethyl L-arginine (LNMMA) on basal renal hemodynamics and the response to infusion of a 10% mixed amino acid solution (1 ml/hr i.v.) in the rat. Renal arterial infusion of LNMMA (500 micrograms/kg/min) resulted in a significant increase in mean arterial pressure, decreases in GFR (20%) and RPF (44%), and a significant increase in filtration fraction. Pretreatment with the angiotensin II receptor antagonist Sar-Gly-angiotensin II did not prevent the increase in blood pressure but blunted the decreases in GFR (11%) and RPF (27%) after LNMMA infusion. Amino acid infusion in the untreated, fasted rat resulted in no change in blood pressure but significant increases in GFR and RPF; these effects were completely inhibited by intrarenal LNMMA but not an equihypertensive intravenous infusion of phenylephrine. In summary, EDRF participates in regulation of basal renal hemodynamics. Furthermore, amino acid-induced hyperfiltration and renal vasodilatation are completely prevented by inhibition of EDRF synthesis. We conclude that EDRF may participate in the renal hemodynamic response to amino acid infusion.

Comparison of converting enzyme inhibitor and calcium channel blocker in hypertensive glomerular injury.

The protective effect of converting enzyme inhibitors in experimental hypertensive glomerular injury is associated with decreased systemic arterial and glomerular capillary pressure. Although calcium channel blockers effectively lower systemic blood pressure, their effect on glomerular capillary pressure and on hypertensive glomerular injury is uncertain. We compared equihypotensive treatment with the calcium antagonist TA 3090 or the converting enzyme inhibitor captopril in post-salt hypertensive Dahl salt-sensitive (DS) rats for up to 5 weeks after five sixths nephrectomy. Before the nephrectomy, all rats demonstrated hypertension (mean 177 mm Hg), proteinuria (mean 175 mg/day), and mild glomerulosclerosis (mean injury score 35). Rats treated with captopril or TA 3090 demonstrated a significant and equivalent decrease in systolic blood pressure compared with untreated rats at 2, 3, and 5 weeks after five sixths nephrectomy; however, only captopril reduced proteinuria. Final proteinuria was actually increased in rats treated with TA 3090 compared with untreated rats. Glomerular injury score was significantly decreased in captopril-treated compared with untreated rats at 2 weeks (33 +/- 9 versus 117 +/- 10, p less than 0.05) and 5 weeks (46 +/- 9 versus 94 +/- 24, p less than 0.05), whereas treatment with TA 3090 delayed but did not prevent progressive glomerular injury (2-week score 35 +/- 7, p less than 0.05 versus untreated; 5-week score 109 +/- 19, p = NS versus untreated). Thus, in hypertensive DS rats after subtotal nephrectomy, treatment with a converting enzyme inhibitor reduced systemic blood pressure, proteinuria, and glomerulosclerosis. However, equihypotensive treatment with a calcium channel blocker did not reduce proteinuria and delayed but did not prevent glomerulosclerosis. Thus, in the rat similar reductions in systemic blood pressure with these two classes of agents have disparate effects on the progression of chronic renal failure.

Role of hypertension in progressive glomerular immune injury.

The relationship between hypertension, ferritin-antiferritin mesangial immune injury (FIC), and progressive glomerular damage was studied in hypertensive (8% NaCl chow) Dahl salt-sensitive rats (DS) and in spontaneously hypertensive rats (SHR). The glomeruli of SHR are protected from the increased perfusion pressure that accompanies systemic hypertension by preglomerular vasoconstriction, while the glomeruli of hypertensive DS are not. Blood pressure, serum creatinine levels, urinary protein excretion, and glomerular injury (assessed by semiquantitative morphometric analysis) were determined in 20-week-old SHR and DS with FIC. In addition, half of a group of 20-week-old SHR with FIC were uninephrectomized and progression of glomerular injury was assessed 12 weeks later. Control rats for each of the groups did not receive FIC. Our studies showed that more extensive mesangial expansion and glomerulosclerosis developed in hypertensive DS with FIC than in rats without FIC. Glomerular injury in DS with FIC affected cortical and deep glomeruli. Similarly, hypertensive SHR with FIC had minimal damage in cortical glomeruli. In deep glomeruli of SHR, mesangial expansion was similar to that of DS, but glomerulosclerosis was absent. In SHR, a 50% reduction in renal mass, a maneuver known to decrease preglomerular vasoconstriction, resulted in mesangial expansion similar to that in DS in cortical glomeruli while deep glomeruli developed mesangial expansion as well as glomerulosclerosis. Our results suggest that when hypertension and mesangial immune injury coexist with renal vasodilatation (as occurs in DS with 2 kidneys and in SHR after uninephrectomy), they act synergistically to induce progressive glomerular damage. Similar mechanisms may be operative in hypertensive humans with glomerulonephritis and may condition the rate of progression to renal insufficiency.

Antihypertensive treatment normalizes decreased endothelium-dependent relaxations in rats with salt-induced hypertension.

Endothelium-dependent responses are impaired in various models of hypertension. The effects of antihypertensive treatment on endothelium-dependent relaxations were studied in Dahl salt-sensitive (DS) and Dahl salt-resistant rats (DR) on a high or low sodium diet. The rats were given either a diet containing 8% NaCl or 0.1% NaCl for 8 weeks or a diet containing 8% NaCl and a combination of reserpine, hydrochlorothiazide, and hydralazine for 8 or 2 weeks. DS on the 8% NaCl diet developed hypertension, while the other rats did not. Antihypertensive therapy for 8 or 2 weeks prevented or reversed hypertension in DS and lowered blood pressure in DR on the 8% NaCl diet. Aortic rings with and without endothelium were suspended in organ chambers for isometric tension recording. In all groups, acetylcholine, adenosine 5'-diphosphate, and thrombin caused endothelium-dependent relaxations. The relaxations in response to all agonists were significantly decreased in DS on 8% NaCl compared to relaxations in the other rats. Antihypertensive treatment for 8 or 2 weeks prevented or reversed the decreased endothelium-dependent relaxations in response to all agonists tested, but not those to the endothelium-independent agonist, sodium nitroprusside. These results suggest that antihypertensive treatment normalizes endothelium-dependent relaxations. This effect of antihypertensive treatment might be important for the prevention of cardiovascular complications in patients with hypertension.

Role of endothelium-derived relaxing factor in regulation of vascular tone and remodeling. Update on humoral regulation of vascular tone.

In addition to preserving the permselectivity of the vascular wall and providing an antithrombogenic surface, the vascular endothelium contributes importantly to the regulation of vasomotor tone. Indeed, the endothelium participates in the conversion of angiotensin I to angiotensin II; the enzymatic inactivation of several plasma constituents such as bradykinin, norepinephrine, serotonin, and ADP; and the synthesis and release of vasodilator substances such as prostacyclin and the recently discovered endothelium-derived relaxing factor (EDRF). The diffusible EDRF released from the endothelium is nitric oxide or a substance closely related to it such as nitrosothiol. The endothelium also synthesizes and releases vasoconstrictive factors, including products derived from arachidonic acid metabolism and the recently discovered peptide endothelin. An increasing body of evidence from experimental and clinical studies indicates that EDRF and endothelium-derived contracting factors play an important role in vascular physiology and pathology. It has become apparent that the balance of these factors may be a major determinant of systemic and regional hemodynamics. Moreover, through generally opposite effects on growth-related vascular changes, contracting factors such as endothelin and relaxing factors such as EDRF also may be important determinants of the vascular response to injury in various disease states such as atherosclerosis and hypertension. It is clear that the vascular endothelium is a complex and dynamic organ. Understanding endothelium function in normal physiology and disease states is of potential clinical importance and should be the focus of future investigation.

High potassium diet augments endothelium-dependent relaxations in the Dahl rat.

Endothelium-dependent relaxations are reduced in hypertensive rats. High dietary potassium supplementation reduces the incidence of strokes in Dahl rats independently of blood pressure, thereby suggesting a direct protective effect of the diet. Endothelium-dependent relaxations and aortic vascular architecture were studied in Dahl salt-sensitive rats fed 8% NaCl, 0.1% NaCl, or 8% NaCl plus 3.6% potassium citrate for 8 weeks. Rats fed 8% NaCl or 8% NaCl plus 3.6% potassium citrate became hypertensive, while those fed 0.1% NaCl did not. Aortic rings with and without endothelium were suspended in organ chambers filled with physiological salt solution (37 degrees C) and aerated with 95% O2, 5% CO2. In rings contracted with norepinephrine, acetylcholine and adenosine 5'-diphosphate caused endothelium-dependent relaxations that were significantly reduced in rats fed 8% NaCl as compared with those fed 0.1% NaCl. Potassium supplementation (8% NaCl/3.6% potassium citrate) significantly enhanced relaxations to acetylcholine in salt-sensitive rats, while those to adenosine 5'-diphosphate and thrombin were either minimally affected or unchanged. Relaxations to sodium nitroprusside were similar in rats with or without potassium supplementation. Hypertension significantly increased aortic medial and intimal thickness. Dietary potassium had no significant effect on the vascular architecture. These results suggest that high potassium diet enhances endothelium-dependent relaxations in Dahl rats at least in part independently of changes in blood pressure. Thus, potassium may be important for its protective effect against stroke and renal damage in this animal model of hypertension.

Endothelium-dependent vascular responses in normotensive and hypertensive Dahl rats.

Experiments were designed to study endothelium-dependent responses in salt-sensitive (DS) and salt-resistant Dahl rats (DR). The rats were fed a low sodium (0.1% NaCl) or high sodium (8% NaCl) diet for 8 weeks. Blood pressure in DS fed a high sodium diet was higher than that in the remaining animals. Aortic rings with and without endothelium were suspended for isometric tension recording. Acetylcholine, adenosine 5'-diphosphate, and thrombin induced endothelium-dependent relaxations that were significantly depressed in the aorta of DS fed a high sodium diet. The relaxations in response to sodium nitroprusside were only slightly, but significantly, depressed in DS fed a high sodium diet. Removal of the endothelium greatly enhanced the response to serotonin and norepinephrine. In rings with, but not without, endothelium taken from rats fed a high sodium diet, the tension developed in response to serotonin and norepinephrine was significantly greater than that in animals fed a low sodium diet. These experiments indicate that endothelium-dependent relaxations to acetylcholine, adenosine 5'-diphosphate, and thrombin are depressed in hypertensive Dahl rats; this effect probably reflects a decreased release of endothelium-derived relaxing factor(s), although structural changes might contribute; and the responsiveness to vasoconstrictor agents is increased in DS and DR fed a high sodium diet. These findings may indicate differential effects of blood pressure and dietary salt on endothelial function.

Hypercholesterolemia promotes endothelial dysfunction in vitamin E- and selenium-deficient rats.

Abnormal regulation of local vascular tone occurs early in human and experimental atherosclerosis. Impaired endothelium-dependent vascular relaxations mediated by endothelium-derived relaxing factor are an important contributor to these abnormalities. Endothelium-derived relaxing factor is nitric oxide released as such or attached to a carrier molecule. Oxidized lipoproteins impede endothelium-derived relaxing factor-mediated responses in vitro. We designed in vivo experiments to determine whether hypercholesterolemia with and without deficiency of two endogenous lipid antioxidants, vitamin E and selenium, would result in endothelial dysfunction. Vitamin E and selenium deficiencies were induced in a group of hypertension-prone Dahl salt-sensitive rats fed a diet high in cholesterol (4%) but low in NaCl (0.5%) for 18 weeks. Two other groups of Dahl salt-sensitive rats received diets sufficient in vitamin E and selenium but containing either high or normal cholesterol levels (control group). Serum cholesterol levels increased approximately 10-fold in the two groups of rats fed high-cholesterol diets. Systolic blood pressure was 143 +/- 3 mm Hg in high-cholesterol/vitamin E- and selenium-sufficient rats and 142 +/- 5 mm Hg in high-cholesterol/vitamin E- and selenium-deficient rats (P = NS). Mild intimal thickening and occasional mononuclear cell infiltration were observed in both of these groups. Serum vitamin E levels were decreased, whereas serum thiobarbituric acid-reactive substances and exhaled pentane (two indicators of endogenous lipid oxidation) were significantly increased in high-cholesterol/vitamin E- and selenium-deficient rats compared with high-cholesterol/vitamin E- and selenium-sufficient rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy and tolerability of losartan in hypertensive patients with renal impairment. Collaborative Group.

We evaluated the blood pressure-lowering activity, tolerability, and safety of losartan in 112 hypertensive (sitting diastolic blood pressure, 90 to 115 mm Hg) patients with chronic renal insufficiency including mild renal insufficiency (30 to 60 mL/min per 1.73 m2; n=51), moderate to severe renal insufficiency (10 to 29 mL/min per 1.73 m2; n=33), or hemodialysis (n=28). After a 3-week placebo period, once-daily losatan was administered for 12 weeks. The daily dose of 50 mg was increased to 100 mg after 4 weeks in patients whose sitting diastolic blood pressure remained > or = 90 mm Hg or was reduced by < 5 mm Hg. A second, non-angiotensin-converting enzyme inhibitor, antihypertensive drug was added after 8 weeks as needed. Twenty-four-hour creatinine clearance was determined and renal clearance studies of inulin and para-aminohippurate were done in a subset of 11 patients. Trough sitting blood pressures were reduced at the end of the first week in all groups. At weeks 4, 8, and 12, the reductions in systolic blood pressure/diastolic blood pressure averaged -11.9/-8.7, -10.8/-9.4, and -14.7/-12.1 mm Hg in patients with mild renal insufficiency; -7.7/-6.3, -13.1/-11.8, and -14.1/-10.6 mm Hg, in moderate to severe renal insufficiency; -17.0/-12.7, -19.1/-14.4, and -22.7/-18.0 mm Hg in hemodialysis. Creatinine clearance, glomerular filtration rate, and effective renal plasma flow were stable. Losartan was withdrawn in only 6 patients because ofa clinical or laboratory adverse experience. Hyperkalemia (> 6 mEq/L) requiring discontinuation of losartan occurred in only one (group 2) patient. We conclude that once-daily losartan, given as monotherapy at doses of 50 or 100 mg or in combination with other antihypertensive drugs, was effective in reducing blood pressure in hypertensive patients with chronic renal disease and that losartan regimens were well tolerated in all groups, including those on hemodialysis.