Milan Ivanov

Losartan improved antioxidant defense, renal function and structure of postischemic hypertensive kidney.

Ischemic acute renal failure (ARF) is a highly complex disorder involving renal vasoconstriction, filtration failure, tubular obstruction, tubular backleak and generation of reactive oxygen species. Due to this complexity, the aim of our study was to explore effects of Angiotensin II type 1 receptor (AT1R) blockade on kidney structure and function, as well as oxidative stress in spontaneously hypertensive rats (SHR) after renal ischemia reperfusion injury. Experiments were performed on anaesthetized adult male SHR in the model of ARF with 40 minutes clamping the left renal artery. The right kidney was removed and 40 minutes renal ischemia was performed. Experimental groups received AT1R antagonist (Losartan) or vehicle (saline) in the femoral vein 5 minutes before, during and 175 minutes after the period of ischemia. Biochemical parameters were measured and kidney specimens were collected 24h after reperfusion. ARF significantly decreased creatinine and urea clearance, increased LDL and lipid peroxidation in plasma. Treatment with losartan induced a significant increase of creatinine and urea clearance, as well as HDL. Lipid peroxidation in plasma was decreased and catalase enzyme activity in erythrocytes was increased after losartan treatment. Losartan reduced cortico-medullary necrosis and tubular dilatation in the kidney. High expression of pro-apoptotic Bax protein in the injured kidney was downregulated after losartan treatment. Our results reveal that angiotensin II (via AT1R) mediates the most postischemic injuries in hypertensive kidney through oxidative stress enhancement. Therefore, blockade of AT1R may have beneficial effects in hypertensive patients who have developed ARF.

Prevention of systemic and regional haemodynamic alterations, hypercreatininemia, hyperuremia and hyperphosphatemia by losartan in hypertension with acute renal failure

Patients with pre-existing hypertension are at a particular risk of fatal outcome due to acute renal failure (ARF). We investigate the effects of angiotensin II type-1 receptor blocker (ARB) losartan, on haemodynamics and biochemical parameters in adult male spontaneously hypertensive rats (SHR) with ischemia/reperfusion ARF. SHR were randomly selected in three experimental groups: sham-operated group (SHAM), ARF group, and ARF+LOS group (losartan, 10 mg/kg/b.w. given by infusion during the period of three hours after reperfusion). Beside the improvement of systemic haemodynamics 24 h after reperfusion, losartan significantly increased renal blood flow (RBF: 19.33±3.29 ml/min/kg vs. 8.03±1.04 ml/min/kg, p<0.05) and decreased renal vascular resistance (RVR) compared to ARF (8.85±1.21 mmHg × min × kg/ml vs. 19.90±2.35 mmHg × min × kg/ml, p<0.001). Plasma creatinine (Pcr), urea (Pu) and phosphates (Pphos) were significantly reduced in ARF+LOS group compared to ARF group (Pcr: 99.11±14.56 μmol/l vs. 242.71±20.25 μmol/l, p<0.001; Pu: 33.72±4.69 mmol/l vs. 61.90±3.93 mmol/l, p<0.001; 2.7±0.42 mmol/l vs. 5.57±0.61 mmol/l, p<0.01). Our results demonstrate that losartan improves systemic and regional haemodynamic and biochemical parameters in hypertension with ARF.

RESVERATROL REDUCES BLOOD PRESSURE, CHANGES OF ANTIOXIDANT ENZYME ACTIVITY AND HISTOLOGICAL PARAMETERS IN EXPERIMENTAL MODEL OF MALIGNANT HYPERTENSION: PP.29.171

Objective: Spontaneously hypertensive rats (SHR) treated with NO syntase inhibitor L-NAME, develop malignant hypertension. This study designed to examine the role of chronic administration of resveratrol on blood pressure, activity of antioxidant enzyme and histological parameters in model of malignant hypertension. Design and Methods: Experiments were performed in adult female SHR, weight 250 g. Two groups of 22 SHR each involved: L-NAME group treated with L-NAME (10 mg/kg per os) and COMB group treated with L-NAME (10 mg/kg per os) and resveratrol (10 mg/kg by gavage). Mean arterial pressure (MAP) and aortal blood flow (ABF) were measured at the end of the 4 weeks treatment period and aortal vascular resistance (AVR) was calculated. Activity of antioxidant enzyme, reduced glutathione (GR) and glutathione peroxidase (GSH-Px) were estimated in erythrocyte. The aorta was preceded for histopathological analysis. Results: The mean arterial pressure after treatment significantly dropped in COMB (157.10 ± 7.49 mmHg) compared L-NAME (182.79 ± 2.16 mmHg). Treatment reduced aortal blood flow that leads to significantly decrease of aortal vascular resistance in COMB (35.54 ± 3.31 mmHg min 100 g/ml) vs L-NAME (45.54 ± 3.06 mmHg min 100 g/ml). Resveratrol in COMB increased activity of GR (30951.23 ± 10253.54 μmol NADPH/min/g Hb) and GSH-Px (9.23 ± 2.10 μmol NADPH/min/g Hb) vs L-NAME (24034.13 ± 5743.76 μmol NADPH/min/g Hb; 3.88 ± 1.14 μmol NADPH/min/g Hb). In model of malignant hypertension histological structure of aorta showed disintegration of endothelial, marked atrophic in tunicae media and necrotic modification in smooth muscle cells. Treatment with resveratrol preserved endothelial and reduced morphological changes in tunica media and smooth muscle cells of aorta. Histopatological score of aorta was significantly reduced in the COMB group (2.50 ± 0.13) compared to L-NAME (3.31 ± 0.12). Conclusions: These results suggest that resveratrol reduced mean arterial pressure and aortal blood flow, probably by decreasing peripheral vascular resistance. Chronic treatment with resveratrol in model of malignant hypertension significantly increased activity of antioxidant enzymes, and reduced morphological changes of aorta. Thus, resveratrol possess antioxidative and antihypertensive effects.

Nitric oxide supplementation in postischemic acute renal failure: normotension versus hypertension.

Nitric oxide (NO) has been suggested to play a pivotal role in ischemic acute renal failure (ARF) but there are controversies about its role in hypertensive and non hypertensive ischemic kidney. Multiple strategies including administration of exogenous NO donors have been shown to protect the kidney against toxic or ischemic injury, suggesting endothelial dysfunction as impaired NO generation due to ischemia. However, in postischemic kidney, NO derived from inducible nitric oxide synthase (iNOS) has been considered to enhance the tissue damage while iNOS inhibition decreased the tubular damage. It is well known decrease in basal production of NO in essential hypertension and that long lasting hypertension damages medium size and small-size blood vessels, therefore predisposes nephroangiosclerosis patients to ARF. Many studies have shown that long term stimulation of NO release in normotension improves renal haemodymnamics and kidney function in ischemic form of ARF. On the other hand, there are studies that have shown that NO synthesis stimulation has no effect or even worsens tubular damage in postischemic hypertensive kidney. Therefore, it seems likely that NO supplementation plays different role in postischemic renal damage development, beneficial in well preserved normotensive kidney and limited in postischemic hypertensive kidney due to disturbed tubuloglomerular response, vasoreactivity and kidney vascular structure.

Upregulation of Heme Oxygenase-1 in Response to Wild Thyme Treatment Protects against Hypertension and Oxidative Stress

High blood pressure is the most powerful contributor to the cardiovascular morbidity and mortality, and inverse correlation between consumption of polyphenol-rich foods or beverages and incidence of cardiovascular diseases gains more importance. Reactive oxygen species plays an important role in the development of hypertension. We found that wild thyme (a spice plant, rich in polyphenolic compounds) induced a significant decrease of blood pressure and vascular resistance in hypertensive rats. The inverse correlation between vascular resistance and plasma heme oxygenase-1 suggests that endogenous vasodilator carbon monoxide generated by heme oxidation could account for this normalization of blood pressure. Next product of heme oxidation, bilirubin (a chain-breaking antioxidant that acts as a lipid peroxyl radical scavenger), becomes significantly increased after wild thyme treatment and induces the reduction of plasma lipid peroxidation in hypertensive, but not in normotensive rats. The obtained results promote wild thyme as useful supplement for cardiovascular interventions.

Macrophage migration inhibitory factor is an endogenous regulator of stress-induced extramedullary erythropoiesis

Macrophage migration inhibitory factor is a well-known proinflammatory cytokine that is released during systemic stress response. Although MIF can affect erythrocyte production, the role of this cytokine in stress-induced erythropoiesis is completely unknown. To extend our previous findings showing that chronic psychological stress stimulates extramedullary erythropoiesis, here we examined whether MIF is involved in the control of stress-induced erythropoietic response. Adult male C57BL/6 wild-type (WT) and MIF-KO (knock-out) mice were subjected to 2-h daily restraint stress for either 7 or 14 consecutive days. The number of erythroid progenitors and CD71/Ter119 profile of erythroid precursors were analyzed in the bone marrow and spleen. Additionally, MIF protein expression was assessed in WT mice. Our results demonstrated that chronic restraint stress enhanced the number of both erythroid progenitors and precursors in the spleen. Stress-induced increase in the number of splenic late erythroid progenitors as well as in the percentage of CD71+Ter119+-double-positive precursors was significantly more pronounced in MIF-KO mice compared to WT animals. Furthermore, repeatedly stressed WT animals demonstrated an augmented MIF expression in the spleen. Unlike the spleen, the bone marrow of chronically stressed WT mice exhibited less prominent changes in erythropoietic stress response and no significant alteration in MIF expression. In addition, MIF deficiency did not influence the bone marrow erythropoiesis in stressed animals. These findings suggest that MIF regulates extramedullary erythropoiesis by inhibiting an overexpansion of splenic immature erythroid cells during chronic stress and indicate a novel role for this cytokine under chronic stress conditions.

Acute Superoxide Radical Scavenging Reduces Blood Pressure but Does Not Influence Kidney Function in Hypertensive Rats with Postischemic Kidney Injury

Acute kidney injury (AKI) is associated with significant morbidity and mortality in hypertensive surroundings. We investigated superoxide radical molecules influence on systemic haemodynamic and kidney function in spontaneously hypertensive rats (SHR) with induced postischemic AKI. Experiment was performed in anesthetized adult male SHR. The right kidney was removed, and left renal artery was subjected to ischemia by clamping for 40 minutes. The treated group received synthetic superoxide dismutase mimetic TEMPOL in the femoral vein 5 minutes before, during, and 175 minutes after the period of reperfusion, while the control AKI group received the vehicle via the same route. All parameters were measured 24 h after renal reperfusion. TEMPOL treatment significantly decreased mean arterial pressure and total peripheral resistance (P < 0.05) compared to AKI control. It also increased cardiac output and catalase activity (P < 0.05). Lipid peroxidation and renal vascular resistance were decreased in TEMPOL (P < 0.05). Plasma creatinine and kidney morphological parameters were unchanged among TEMPOL treated and control groups. Our study shows that superoxide radicals participate in haemodynamic control, but acute superoxide scavenging is ineffective in glomerular and tubular improvement, probably due to hypertension-induced strong endothelial dysfunction which neutralizes beneficial effects of O2 − scavenging.

Chronic changes of hematocrit value alter blood pressure and glomerular filtration in spontaneously hypertensive rats

Many studies in hypertensive humans and animals have shown that increased blood viscosity is in direct relation with essential hypertension. The aim of our studies was to investigate the effects of chronic hematocrit value changes on arterial blood pressure and kidney function in genetically induced hypertension. To this end, we studied the effects of several interventions, designed to increase/decrease hematocrit, on hemodynamic parameters, vascular reactivity, glomerular filtration and renal function curve in spontaneously hypertensive rats (SHR). Results of our study show that chronic hematocrit value elevation increases blood pressure and peripheral vascular resistance in SHR. On the other hand, chronic hematocrit lowering elucidates blood pressure and peripheral vascular resistance decrease followed by cardiac output rising. Both hematocrit value changes significantly reduce vasodilatory vascular response. Hematocrit lowering induces acute renal failure. Sodium excretion is shifted to higher blood pressure values in high hematocrit value animals and opposite - lower blood pressure values in low hematocrit value animals. Repeated transfusions develop salt sensitive malignant hypertension in SHR. Further studies are necessary to evaluate the degree of kidney damage after chronic hematocrit value changes in SHR.

Effects of Losartan, Tempol, and Their Combination On Renal Nitric Oxide Synthases in the Animal Model of Chronic Kidney Disease

Abstract Down-regulation of nitric oxide synthase (NOS) and NO deficiency in the kidneys have been implicated in the pathogenesis of chronic kidney disease (CKD). In this study we examined the effects of losartan, tempol, and combined treatment on three NOS isoforms expressions, kidney NO content and NOS correlation with renal function and structure in the early stage of adriamycin (ADR)-induced CKD in spontaneously hypertensive rats (SHR). Rats were divided into control group, and four other groups which were treated with ADR and received vehicle, losartan (L, angiotensin II type 1 receptor blocker), tempol (T, redox-cycling nitroxide) or T+L treatment (by gavage) in a six-week study. Reduction of all NOS isoforms expressions were significantly improved by losartan or tempol, and correlated with proteinuria amelioration. Combined treatment induced down-regulation of constitutive NOS isoforms, whilst inducible NOS was up-regulated and followed by increased nitrite content and a significant decline in the glomerular filtration rate. Losartan or tempol prevented ADR-induced neoexpression of vimentin in the glomeruli and tubulointerstital areas, whereas de novo vimentin expression was still observed in the atrophic tubules and in the interstitial fibroblasts and myofibroblasts in combined treatment. It can be concluded that single treatments, contrary to combined, were effective in improving NO bioavailability and slowing down the progression of CKD.

[PP.31.09] URTICA DIOICA L. LEAF EXTRACT REDUCES BLOOD PRESSURE AND IMPROVES ANTIOXIDATIVE DEFENCE IN SPONTANEOUSLY HYPERTENSIVE RATS

Objective: Stinging nettle (Urtica dioica L.) has been traditionally used in treatment numerous health problems, including hypertension and hyperlipidemia. The aim of this study was to evaluate potential antihypertensive and antioxidant effects of chronic intake of stinging nettle leaf extract (UE) in spontaneously hypertensive rats (SHR). Design and method: SHR were divided into 5 experimental groups. Throughout 4 weeks long study, control group (SHRC) received tap water, positive antihypertensive control group (SHR+L) received 10 mg/kg/day of losartan, while SHR+UE10, SHR+UE50 and SHR+UE200 groups were treated with 10, 50, and 200 mg/kg/day of dry aqueous-methanolic UE. Losartan and UE were dissolved in 0.5 ml of water, and given to the animals by gavage. At the end of the treatment mean arterial pressure (MAP) was measured directly in anesthetized animals, and blood samples were collected for erythrocyte superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities. Serum lipid peroxidation level was assessed by total thiobarbituric acid-reactive substances assay (TBARS). Results: MBP dropped significantly in SHR+L, SHR+UE50, and SHR+UE200 group. Furthermore, all three UE doses significantly increased SOD and CAT activities, but not the GPx activity. Antioxidant enzyme activities remained unchained in SHR+L group. Serum lipid peroxidation level was decreased in all three tested UE doses while it remained unchanged in SHR+L group. Figure. No caption available. Conclusions: Our results indicate that all three UE doses improve antioxidant enzymes activity and reduce serum lipid peroxidation level in SHR. Furthermore, MAP reduction in SHR+UE50 and SHR+UE200 is similar to losartan therapy. Therefore, UE expresses beneficial effects in genetically induced hypertension.