Renal effects of FK453: A potent non-xanthine adenosine A1 receptor antagonist

The renal effects of FK453, a potent and selective non-xanthine adenosine A₁ receptor antagonist, were examined and compared with FR113452 (less active enantiomer of FK453), typical adenosine receptor antagonists, and diuretics. In rats FK453 possessed diuretic activity similar to 1, 3-dipropyl-8-cyclopentylxanthine (DPCPX, adenosine A₁ receptor antagonist), hydrochlorothiazide, and furosemide, but neither FR113452 nor CP66713 (an adenosine A₂ receptor antagonist) possessed diuretic activity. Urinary uric acid excretion in rats increased with FK453, but other drugs had no effect. These diuretic and uricosuric activities of FK453 were also observed in dogs. In anesthetized dogs, FK453 increased the renal blood flow (RBF), inulin clearance (Cin), and p-aminohippuric acid clearance (C_PAH). However, hydrochlorothiazide had no effect on RBF, Cin, and C_PAH. Furthermore, osmolar clearance experiments suggested that the renal site of action of FK453 was different from hydrochlorothiazide and furosemide. These results demonstrate that FK453 has diuretic activity and increases urinary uric acid excretion and suggest that the diuretic activity of FK453 is related to adenosine A₁ receptor antagonism; also, the diuretic mechanism of action and the renal site of action of FK453 are different from those of hydrochlorothiazide and furosemide. FK453 is a useful compound to clarify the physiological role of the adenosine A₁ receptor in the kidney. © 1995 Wiley-Liss, Inc.     

松花粉对甘油诱导大鼠急性肾衰竭的保护作用

目的：研究松花粉对甘油诱发大鼠急性肾衰竭（acute renal failure,ARF）的保护作用及机制。方法：采用双侧后肢注射50%甘油溶液（10 mL·kg-1）诱发大鼠成急性肾衰竭模型,检测大鼠血清肌酐（Scr）、血清尿素氮（BUN）的含量,肾组织中超氧化物歧化酶（SOD）的活性,谷胱甘肽（GSH）、丙二醛（MDA）的含量,同时测定肾组织中一氧化氮（NO）的含量和诱导型一氧化氮合酶（iNOS）的活性;HE染色观察肾病理组织形态学变化。结果：与空白组大鼠相比,模型组大鼠血清Scr和BUN的含量明显上升,肾组织中SOD的活性和GSH的含量显著降低,MDA的含量显著升高;组织病理检查发现,模型组大鼠肾小管损伤明显,肾皮质细胞部分脱落,肾小球肿胀,间质炎性侵润明显。给予松花粉治疗后,可显著降低ARF大鼠血清Scr和BUN,升高肾组织中SOD的活性、GSH的含量,降低MDA的含量,同时发现,松花粉可明显降低肾组织中NO的含量和iNOS的活性,并显著降低肾组织损伤。结论：松花粉对甘油致大鼠ARF具有治疗作用,其作用机制可能与抑制iNOS的活性,降低体内NO过多产生,降低NO相关的脂质过氧化过程有关。     

Protective effects of L-carnitine on myoglobinuric acute renal failure in rats

1. Muscle injury (rhabdomyolysis) is one of the causes of acute renal failure (ARF). Iron, free radicals and nitric oxide (NO) play a critical role in the pathogenesis of glycerol-induced myoglobinuric ARF. L-Carnitine is an anti-oxidant and prevents the accumulation of end-products of lipid peroxidation. Therefore, the aim of the present study was to investigate the effects of L-carnitine on myoglobinuric ARF induced by intramuscular (i.m.) hypertonic glycerol injection. 2. Sprague-Dawley rats were divided into three groups. Rats in group 1 (n = 8) were given saline, whereas those in groups 2 (n = 10) and 3 (n = 10) were injected with glycerol (10 mL/kg, i.m.). Concomitant with and 24 h after glycerol injection, L-carnitine (200 mg/kg, i.p.) was administered to group 3 rats. Forty-eight hours after glycerol injection, blood samples and kidney tissues were taken from anaesthetised rats. 3. Plasma creatine kinase (CK) activity, urea, creatinine and NO levels, as well as kidney tissue superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) enzyme activity and malondialdehyde (MDA) and glutathione (GSH) levels, were determined. In the kidney tissue, histopathological changes and iron accumulation in the tubular epithelium were also investigated. 4. Glycerol treatment caused severe ARF: a marked renal oxidative stress, significantly increased CK activity, urea and creatinine levels and decreased plasma NO levels. Histopathological findings in group 2 rats confirmed that there was renal impairment by cast formation and tubular necrosis and a marked increase in iron accumulation in the tubular epithelium. All these factors were significantly improved by L-carnitine supplementation. 5. These results may indicate that L-carnitine treatment protects against functional, biochemical and morphological damage and iron accumulation in glycerol-induced myoglobinuric ARF in rats. In this model, the protective effect of L-carnitine treatment may provide a new insight into the treatment of rhabdomyolysis-related ARF.     

Haemodynamic effects of a selective adenosine A2A receptor agonist,CGS 21680, in chronic heart failure in anaesthetized rats

1. Recently we demonstrated that the administration of an A_2A adenosine receptor agonist, CGS 21680, to anaesthetized rats with acute heart failure (1 h post-coronary artery ligation) resulted in an increase in cardiac output. In the present investigation, the effects of CGS 21680 on cardiac output, vascular resistance, heart rate, blood pressure and mean circulatory filling pressure (Pmcf) were investigated in anaesthetized rats with chronic heart failure (8 weeks post-coronary artery ligation).
2. Experiments were conducted in five groups (n=6) of animals: sham-operated vehicle-treated (0.9% NaCl; 0.037 mL kg⁻¹ min⁻¹) animals in which the occluder was placed but not pulled to ligate the coronary artery; coronary artery-ligated vehicle-treated animals; and coronary artery-ligated CGS 21680-treated (0.1, 0.3 or 1.0 μg kg⁻¹ min⁻¹) animals.
3. Baseline blood pressure, cardiac output and rate of rise in left ventricular pressure (+dP/dt) were significantly reduced in animals with coronary artery ligation when compared to sham-operated animals. Coronary artery ligation resulted in a significant increase in left ventricular end-diastolic pressure, Pmcf and venous resistance when compared to sham-operated animals.
4. Administration of CGS 21680 at 0.3 and 1.0 μg kg⁻¹ min⁻¹ significantly (n=6; P<0.05) increased cardiac output by 19±4% and 39±5%, and heart rate by 14±2% and 15±1%, respectively, when compared to vehicle treatment in coronary artery-ligated animals. Administration of CGS 21680 also significantly reduced blood pressure and arterial resistance when compared to coronary artery-ligated vehicle-treated animals. Infusion of CGS 21680 also significantly reduced venous resistance when compared to vehicle-treated coronary artery-ligated animals.
5. The results show that heart failure is characterized by reduced cardiac output, and increased left ventricular end-diastolic pressure, venous resistance and Pmcf. Acute treatment with CGS 21680 in animals with chronic heart failure decreased left ventricular end-diastolic pressure and increased cardiac output. This increase in cardiac output was the result of reduced arterial and venous resistances and increased heart rate.

     

Protective effect of γ-aminobutyric acid against glycerol-induced acute renal failure in rats

To investigate the effect of γ-aminobutyric acid (GABA) on acute renal failure, we used a rat model of acute tubular necrosis induced by glycerol. After deprivation of water for 6 h, the rats received an injection of 50% glycerol into the muscle of the rear limb at 10 ml/kg body weight. GABA was then administered orally to the rats (100 or 500 mg/kg body weight/day) once every 12 h for 3 days. The rats with acute renal failure showed arrested body weight gain and an increase of kidney weight, whereas oral administration of GABA attenuated the physiological changes induced by acute renal failure. However, GABA administration had no significant effect on increased urine volume. Oral administration of GABA at a dose of 100 or 500 mg/kg body weight/day for 3 days significantly improved the markedly elevated levels of blood urea nitrogen and creatinine and the reduced creatinine clearance related to progression of renal failure. Moreover, the rats with acute renal failure exhibited high levels of fractional excretion of sodium (FE_Na) due to alteration of tubule function following injection of glycerol. However, administration of GABA lowered the FE_Na levels dose-dependently. Furthermore, urine osmolarity was markedly reduced in control rats with acute renal failure as compared with normal rats, whereas it was significantly increased by administration of GABA at a dose of 500 mg/kg body weight/day. These results indicate that GABA has potential as a therapeutic agent against the renal damage involved in acute renal failure.     

双参苓颗粒剂对慢性肾功能衰竭大鼠肾脏的保护作用

目的观察双参苓颗粒剂对单侧肾切除大鼠慢性肾功能衰竭(CRF)的保护作用。方法通过单侧肾切除加尾静脉重复注射柔红霉素,复制大鼠慢性肾衰模型,动物随机分成6组:正常组、模型组、尿毒清颗粒剂组、双参苓颗粒剂高、中、低剂量(2.70,1.35,0.68 g.kg-1.d-1)实验组,连续给药6周后,检测各组血液学指标、血清生化指标,HE染色观察大鼠肾脏组织病理学变化。结果双参苓颗粒剂高、中剂量(2.70,1.35 g.kg-1.d-1)组的尿蛋白、血清肌酐、尿素氮、甘油三脂和胆固醇水平,显著低于模型组;血浆白蛋白、红细胞、血红蛋白和红细胞压积,明显高于模型组;肾组织病理损伤明显轻于模型组。结论双参苓颗粒剂对CRF大鼠残肾功能有保护作用,呈剂量依赖趋势。     

The adenosine A1 receptor antagonist SLV320 reduces myocardial fibrosis in rats with 5/6 nephrectomy without affecting blood pressure

BACKGROUND AND PURPOSE: Myocardial fibrosis is an unwanted effect associated with chronic renal failure. The adenosine system is involved in cardiac and renal function. Therefore, we investigated the novel selective adenosine A(1) receptor antagonist SLV320 focusing on its potential in preventing cardiomyopathy in rats with 5/6 nephrectomy. EXPERIMENTAL APPROACH: Male Sprague-Dawley rats were allocated to 4 groups of 12 rats each: 5/6 nephrectomy (5/6 NX), 5/6 NX plus SLV320 (10 mg kg(-1) d(-1) mixed with food), sham and sham plus SLV320. Study duration was 12 weeks, blood pressure was assessed repeatedly. At study end kidney function was assessed, blood samples and hearts were taken for histology/immunohistochemistry. Pharmacological properties of SLV320 were assessed using receptor binding and enzyme assays and in vivo. KEY RESULTS: SLV320 is a selective and potent adenosine A(1) antagonist in vitro (Ki=1 nM) with a selectivity factor of at least 200 versus other adenosine receptor subtypes. Functional A(1) antagonism was demonstrated in vivo. In rats with 5/6 NX SLV320 significantly decreased albuminuria by about 50%, but did not alter glomerular filtration rate (GFR). SLV320 normalized cardiac collagen I+III contents in 5/6 NX rats. SLV320 prevented nephrectomy-dependent rise in plasma levels of creatinine kinase (CK), ALT and AST. Blood pressure did not differ between study groups. CONCLUSION: SLV320 suppresses cardiac fibrosis and attenuates albuminuria without affecting blood pressure in rats with 5/6 nephrectomy, indicating that selective A(1) receptor antagonists may be beneficial in uraemic cardiomyopathy.     

Effects of caffeic acid phenethyl ester on glycerol-induced acute renal failure in rats

1. Free radicals and nitric oxide (NO) play a crucial role in the pathogenesis of myoglobinuric acute renal failure (ARF). The aim of the present study was to investigate the effects of caffeic acid phenethyl ester (CAPE), an anti-oxidant, on the myoglobinuric ARF induced by intramuscular hypertonic glycerol injection. 2. Thirty rats were divided equally into three groups. Rats in group 1 were given saline and those in groups 2 and 3 were injected with glycerol (10 mL/kg, i.m.). Concomitant and 24 h after glycerol injection, CAPE (10 micromol/kg, i.p.) was administered to group 3 rats. Forty-eight hours after glycerol injection, blood samples and kidney tissues of rats were taken under anaesthesia. 3. Plasma concentrations of urea, creatinine, malondialdehyde (MDA) and NO were determined, as were superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) activities and MDA levels in kidney tissues. Kidney morphology was also investigated. 4. In the group receiving CAPE, although SOD enzyme activity was found to be increased, we failed to find any protective effect of CAPE on other parameters investigated. Moreover, although CAPE significantly decreased NO levels, it increased plasma concentrations of urea and MDA. 5. We suggest that the effect of CAPE in decreasing NO concentrations may further increase the renal ischaemia in this model. Thus, CAPE may have a worsening rather than beneficial effect under these conditions in this model of ARF.     

虫草多糖对庆大霉素诱发的急性肾衰的预防作用

目的：探讨虫草多糖对庆大霉素诱发的急性肾衰的防治作用。方法：将实验动物分为阳性地塞米松磷酸钠组,虫草多糖高、中、低剂量组以及正常对照组、模型组;采用腹腔注射庆大霉素的方法复制大鼠急性肾衰（ARF）模型,造模过程中预防给药。观察大鼠的血液生化指标、肾功能、肾病理、肾指数等指标的变化。结果：预防给药后,阳性对照组和虫草多糖3个剂量组大鼠的血清尿素氮、肌酐的含量,以及尿蛋白和尿量降低,与模型组比较有显著差异（P〈0．01或P〈0．05）,高剂量和中剂量虫草多糖的作用优于阳性对照组。病理切片可见阳性对照组和虫草多糖高剂量组大鼠肾脏病理损伤明显好转,优于中、低剂量组。结论：虫草多糖能够预防大鼠庆大霉素诱发的急性肾衰,改善肾功能。     

Comparative study on altered hepatic metabolism of CYP3A substrates in rats with glycerol-induced acute renal failure

To examine the mechanism accounting for the diverse alteration of hepatic metabolism of CYP3A substrates observed with renal function being severely impaired, the hepatic drug metabolizing activity was evaluated using liver microsomes prepared from rats with glycerol-induced acute renal failure (ARF). Midazolam, nifedipine and rifabutin were employed as representative CYP3A substrates. When the Michaelis-Menten parameters, K(m) and V(max) , were examined in the incubation study, the K(m) values of midazolam and nifedipine in ARF rats were shown to decrease by 50.9% and 29.9% compared with the normal value, respectively. The V(max) values of midazolam and nifedipine in ARF rats also decreased by 49.3% and 28.0%, respectively, showing that their decreased K(m) values accompanied the decreased V(max) values. The parameters of nifedipine seemed to alter to a lesser extent than those of midazolam. As for rifabutin metabolism, the decrease in the K(m) value was observed in ARF rats, but it did not accompany the decrease in the V(max) value. Then, the hepatic expressions of the CYP3A subfamily were examined with western blotting using anti-CYP3A1 and anti-CYP3A2 antibodies. It was revealed that the hepatic expression of CYP3A2 decreased, while that of CYP3A1 was unaffected. Additionally, a band signal deduced to originate from CYP3A9 was clearly detected in ARF, but not in normal rats. Considering each substrate having different specificities for CYP3A subfamily member proteins, individual alterations of hepatic CYP3A subfamily expression seem to underlie the diverse alterations of hepatic metabolism of CYP3A substrates in ARF rats.     

Pharmacological investigations of Punica granatum in glycerol-induced acute renal failure in rats

Objective:

The present study was designed to investigate the ameliorative potential and possible mechanism of hydroalcoholic extract of flowers of P. granatum in glycerol-induced acute renal failure (ARF) in rats.

Materials and Methods:

The rats were subjected to rhabdomyolytic ARF by single intramuscular injection of hypertonic glycerol (50% v/v; 8 ml/kg) and the animals were sacrificed after 24 hours of glycerol injection. The plasma creatinine, blood urea nitrogen, creatinine clearance, and histopathological studies were performed to assess the degree of renal injury.

Results:

Pretreatment with hydroalcoholic extract of flowers of P. granatum (125 and 250 mg/kg p.o. twice daily for 3 days) significantly attenuated hypertonic glycerol-induced renal dysfunction in a dose-dependent manner. BADGE (Bisphenol-A-diglycidyl ether) (30 mg/kg), a peroxisome proliferator-activated receptor (PPAR)-γ antagonist, and N(omega)-nitro-l-arginine-methyl ester (L-NAME) (10, 20, and 40 mg/kg), nitric oxide synthase inhibitor, were employed to explore the mechanism of renoprotective effects of Punica granatum. Administration of BADGE (30 mg/kg) and L-NAME (40 mg/kg) abolished the beneficial effects of P. granatum in glycerol-induced renal dysfunction.

Conclusion:

Hydroalcoholic extract of flowers of P. granatum has ameliorative potential in attenuating myoglobinuric renal failure and its renoprotective effects involve activation of PPAR-γ and nitric oxide-dependent signaling pathway.     

Differential effects of the adenosine A1 receptor agonist adenosine amine congener on renal, femoral and carotid vascular conductance in preterm fetal sheep

1. Adenosine A(1) receptor activation is critical for endogenous neuroprotection from hypoxia-ischaemia, raising the possibility that treatment with A(1) receptor agonists may be an effective physiological protection strategy for vulnerable preterm infants. However, the A(1) receptor can mediate unwanted systemic effects, including vasoconstriction of the afferent glomerular arteriole. There is limited information on whether this occurs at doses that improve cerebral perfusion in the immature brain. 2. Therefore, in the present study, we examined whether infusion of the selective A(1) receptor agonist adenosine amine congener (ADAC) is associated with reduced renal perfusion in chronically instrumented preterm (0.7 gestation) fetal sheep. In the present study, ADAC was given in successive doses of 2.5, 5.0 and 15.0 microg, 45 min apart. 3. Treatment with ADAC was associated with a marked reduction in renal vascular conductance (and blood flow), whereas carotid conductance was increased and there was no significant effect on femoral conductance. In contrast with the stable effects of increasing ADAC dose on vascular conductance, there was a significant dose-related fall in fetal heart rate and blood pressure. 4. In conclusion, these short-term data support the concern that A(1) receptor agonist infusion can selectively impair renal perfusion, even at low doses.     

General pharmacology of SDZ WAG 994, a potent selective and orally active adenosine A1 receptor agonist

The pharmacological properties of 6-cyclohexyl-2′-0-methyladenosine (SDZ WAG 994)—a potent, selective, and orally active adenosine A₁ receptor agonist—are described. SDZ WAG 994 is a potent (K_D 23 ± 2 nM, n = 5) and selective (1,090-fold vs. A_2A receptors) displacer of binding to pig striatal A₁ receptors and behaves as a full agonist at the A₁ receptors coupled negatively to adenylate cyclase in rat adipocytes (pEC₅₀ 6.4 ± 0.2, n = 3), those which induce contraction of rat spleen (pEC₅₀ 7.1 ± 0.1, n = 13) and those which suppress the response to autonomic nerve stimulation in guinea-pig ileum (pIC₅₀ 6.6 ± 0.1, n = 4) and rat kidney (pIC₅₀ 6.0 ± 0.1, n = 6). The compound has negligible affinity (pEC₅₀ < 4, n = 5) for the A_2B receptor which mediates relaxation of guinea-pig aorta. In spontaneously hypertensive (SH) rats SDZ WAG 994, 0.05–0.5 mg/kg (0.14–1.4 μmol/kg) po, caused dose-related and sustained (> 5 h) falls in blood pressure (BP) and heart rate (HR) and suppressed plasma renin activity (PRA); the cardiovascular effects could be immediately and fully reversed by an intravenous injection of 8-(p-sulphophenyl)theophylline, 20 mg/kg (56.4 μmol/kg). SDZ WAG 994 given via the food at 0.4 and 1.2 mg/kg/day (1.1 and 3.3 μmol/kg/day) for 7 or 14 days, respectively, induced dose-related hypotension and bradycardia which were well maintained throughout the treatment periods. In the conscious, normotensive dog, SDZ WAG 994, 1 and 3 mg/kg (2.8 and 8.3 μmol/kg) po, induced substantial, sustained falls in BP which were accompanied by tachycardia. In salt depleted squirrel monkeys, SDZ WAG 994, 0.1–0.3 mg/kg (0.28–0.83 m?mol/kg) iv or 0.2–0.6 mg/kg (0.56–1.7 μmol/kg) po caused dose-related and sustained (> 5 h) bradycardia and suppression of PRA but no change in BP. In rhesus monkeys, SDZ WAG 994, 0.1–1.2 mg/kg (0.28–3.3 μmol/kg) po induced sustained bradycardia and suppression of PRA and the plasma free fatty acid and triglyceride concentrations. The data establish SDZ WAG 994 as a potent, selective, and orally active adenosine A₁ receptor agonist with therapeutic potential in certain cardiovascular and/or metabolic disease states. © 1995 Wiley-Liss, Inc.     

Effect of the adenosine antagonist 8-phenyltheophylline on glycerol-induced acute renal failure in the rat.

8-Phenyltheophylline (8-PT)(10 mg kg-1) or its vehicle(1 ml kg-1) were administered intravenously or intraperitoneally twice daily over 48 h to rats with acute renal failure (ARF) induced by intramuscular (i.m.) injection of glycerol. Rats treated with 8-PT i.v. had significantly lower plasma urea and creatinine levels at 24 and 48 h compared to untreated animals. The vehicle also reduced plasma urea and creatinine when compared to untreated controls. However, plasma urea levels in 8-PT-treated rats were significantly lower than in vehicle-treated animals at 24 and 48 h after both i.v. and i.p. administration. Plasma creatinine concentrations also tended to be lower in the 8-PT-treated group. [3H]-inulin clearance at 48 h after i.m. glycerol was significantly greater in rats dosed i.p. with 8-PT compared to either untreated or vehicle treated rats. Examination of kidneys taken from rats 48 h after i.m. glycerol showed that 8-PT treatment significantly reduced renal damage and kidney weight compared to the untreated or vehicle-treated groups. In a 7 day study all the rats which received 8-PT i.p. survived whilst in the vehicle and untreated groups the mortality rates were 12 and 21% respectively. In a separate series of experiments 8-PT (10 mg kg-1, i.v. or i.p.) was found to antagonize adenosine-induced bradycardia in conscious rats for up to 5 h. There is no clear explanation for the partial protection afforded by the vehicle but it may be related to either its alkalinity or an osmotic effect produced by the polyethylene glycol component.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protective effect of alpha-lipoic acid against ischaemic acute renal failure in rats

1. In the present study, we investigated whether treatment with alpha-lipoic acid (LA), a powerful and universal anti-oxidant, has renal protective effects in rats with ischaemic acute renal failure (ARF). 2. Ischaemic ARF was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Blood urea nitrogen (BUN), plasma concentrations of creatinine (Pcr) and urinary osmolality (Uosm) were measured for the assessment of renal dysfunction. Creatinine clearance (Ccr) and fractional excretion of Na+ (FENa) were used as indicators of glomerular and tubular function, respectively. 3. Renal function in ARF rats decreased markedly 24 h after reperfusion. Intraperitoneal injection of LA at a dose of 10 mg/kg before the occlusion tended to attenuate the deterioration of renal function. A higher dose of LA (100 mg/kg) significantly (P < 0.01) attenuated the ischaemia/reperfusion-induced increases in BUN (19.1 +/- 0.7 vs 7.2 +/- 0.7 mmol/L before and after treatment, respectively), Pcr (290 +/- 36 vs 78.1 +/- 4.2 micromol/L before and after treatment, respectively) and FENa (1.39 +/- 0.3 vs 0.33 +/- 0.09% before and after treatment, respectively). Treatment with 100 mg/kg LA significantly (P < 0.01) increased Ccr (0.70 +/- 0.13 vs 2.98 +/- 0.27 mL/min per kg before and after treatment, respectively) and Uosm (474 +/- 39 vs 1096 +/- 80 mOsmol/kg before and after treatment, respectively). 4. Histopathological examination of the kidney of ARF rats revealed severe lesions. Tubular necrosis (P < 0.01), proteinaceous casts in tubuli (P < 0.01) and medullary congestion (P < 0.05) were significantly suppressed by the higher dose of LA. 5. A marked increase in endothelin (ET)-1 content in the kidney after ischaemia/reperfusion was evident in ARF rats (0.43 +/- 0.02 ng/g tissue) compared with findings in sham- operated rats (0.20 +/- 0.01 ng/g tissue). Significant attenuation (P < 0.01) of this increase occurred in ARF rats treated with the higher dose of LA (0.24 +/- 0.03 ng/g tissue). 6. These results suggest that administration of LA to rats prior to development of ischaemic ARF prevents renal dysfunction and tissue injury, possibly through the suppression of overproduction of ET-1 in the postischaemic kidney.     

NPC 205 is a potent and selective adenosine A1, receptor antagonist: Correlation among receptor binding,biochemical, and physiological assays

The chemical synthesis of 8-aryl-1,3-dialkyl derivatives of xanthine and the ability of these compounds to interact with adenosine A₁ and A₂ receptors in vitro (in receptor binding, biochemical, and physiological assays) are described. NPC 205 (1,3-dipropyl-8-[4-hydroxy- phenyl]xanthine) was the most potent and A₁-selective antagonist of the series. NPC 205 was twice as potent at PACPX (1,3-dipropyl-8-[2-amino-4-chlorophenyl]xanthine) and at least 20-fold more potent than 8-phenyltheophylline to inhibit specific binding of [³H]-cy-clohexyladenosine to guinea pig and rat brain membranes. Along with NPC 189 (1,3-dimethyl-8-[4-hydroxyphenyl]xanthine), NPC 200 (1,3-dipropyl-8-phenylxanthine), and PACPX, NPC 205 also was a more potent antagonist of A₁-receptor-mediated inhibition of adenylate cyclase (AC) in rat cortex than A₂ receptor-coupled stimulation of AC in PC-12 cell membranes. NPC 205 was, in fact, 30-fold more potent and fourfold more selective than PACPX for the AC-coupled A₁ receptor function and exhibited competitive interactions with A₁ receptors. In isolated guinea pig atria, NPC 205, NPC 189, NPC 200, and PACPX all reversed 5′N-ethyl-carboxamidoadenosine (NECA)-induced depression of tension and rate. In the Langendorff isolated perfused guinea pig heart preparation, NPC 205 was more potent than PACPX in reversing NECA-mediated depression in developed tension and rate (A₁-mediated) and, unlike PACPX, had no effect on coronary perfusion pressure (A₂-mediated). Neither NPC 205 or PACPX had significant competitive inhibitory effects on rat heart phosphodiesterase III activity in vitro. Together, the results suggest that NPC 205 is a highly potent, selective, and competitive antagonist of adenosine A₁ receptors and should be useful for examining the physiological significance of A₁ receptors in vitro and in vivo.     

Dietary curcumin does not protect kidney in glycerol-induced acute renal failure.

Generation of reactive oxygen species significantly contribute to the pathogenesis of renal injury induced by myoglobin release. The present study was performed to investigate the effects of dietary curcumin, a natural antioxidant isolated from plant Curcuma longa, in an experimental model of myoglobinuric acute renal failure. Rats received curcumin at an oral dose of 100mg/kg/day for 30 days. Renal injury was induced with injection of hypertonic glycerol (10 ml/kg 50% solution) in hind limb muscle with blood urea of 57.8+/-7.2 vs. 7.72+/-1.03 mmol/l and serum creatinine of 444.4+/-61.3 vs. 51.8+/-10.6 micromol/l, in glycerol-induced acute renal failure (ARF) vs. control rats, respectively. After 48 h rats were sacrificed and thiobarbituric acid reactive substance (TBARS), glutathione, carbonyl content and kidney cortex brush border peptidase activities were determined in serum, kidney and liver. Rats that received curcumin in addition to glycerol had significantly lower TBARS in serum but not in kidney and liver. Carbonyl content in kidney and liver was significantly elevated in curcumin and glycerol treated rats and improved in animals treated with curcumin and glycerol together. The activities of kidney cortex enzymes, aminopeptidase N, angiotensinase A and dipeptidyl peptidase IV, were reduced in glycerol as well as in curcumin treated rats. The results obtained in this study provided additional evidence that despite its limited antioxidant activity curcumin did not protect kidney in myoglobinuric model of ARF.     

Protective effect of naringin, a bioflavonoid on glycerol-induced acute renal failure in rat kidney

Rhabdomyolysis-induced myoglobinuric acute renal failure accounts for about 10-40% of all cases of acute renal failure (ARF). Reactive oxygen intermediates have been demonstrated to play an etiological role in myoglobinuric renal failure. This study was designed to investigate the effect of naringin, a bioflavonoid with antioxidant potential, in glycerol-induced ARF in rats. Five groups of rats were employed in this study, group I served as control, group II was given 50% glycerol (8 ml/kg, intramuscularly), group III, IV, and V were given glycerol plus naringin 100, 200, and 400mg/kg p.o. route, respectively) 60 min prior to the glycerol injection. Renal injury was assessed by measuring plasma creatinine, blood urea nitrogen, creatinine, and urea clearance. The oxidative stress was measured by renal malondialdehyde levels, reduced glutathione levels, and by enzymatic activity of catalase, glutathione reductase, and superoxide dismutase. Glycerol treatment resulted in a marked renal oxidative stress and significantly deranged the renal functions. Pretreatment of animals with naringin 60 min prior to glycerol injection markedly attenuated renal dysfunction, morphological alterations, reduced elevated thiobarbituric acid reacting substances (TBARS), and restored the depleted renal antioxidant enzymes. These results clearly demonstrate the role of oxidative stress and its relation to renal dysfunction, and suggest a protective effect of naringin in glycerol-induced renal failure in rats.     

Effects of CGS 21680, a selective A2A adenosine receptor agonist,on cardiac output and vascular resistance in acute heart failure in the anaesthetized rat

1. The effects of CGS 21680, a selective A_2A adenosine receptor agonist, on cardiac output, blood pressure, mean circulatory filling pressure (P_mcf), arterial and venous resistances, heart rate and left ventricular end-diastolic pressure were assessed in rats with acute heart failure by means of coronary artery occlusion.
2. Animals (n=6 in each group) were divided into five groups: group I, sham-operated vehicle-treated (0.9% saline; 0.018 mL min⁻¹); groups II-V, subject to coronary artery occlusion and treated with vehicle (0.9% saline; 0.018 ml min⁻¹) and CGS 21680 (0.1, 0.3 and 1.0 μg kg⁻¹ min⁻¹), respectively. Haemodynamic measurements were taken one hour after completion of surgery, ninety minutes after coronary artery occlusion (except in group I), and fifteen minutes after infusion of saline or CGS 21680.
3. Baseline haemodynamic measurements before occlusion were found not to differ significantly between the different groups of animals. However, after occlusion, cardiac output, rate of rise in left ventricular pressure (+dP/dt) and blood pressure were significantly reduced when compared to corresponding values in sham-operated animals. In addition, occlusion of the coronary artery resulted in a significant elevation in venous resistance, P_mcf and left ventricular end-diastolic pressure as compared to corresponding values in sham-operated animals.
4. Infusion with CGS 21680 at the highest dose significantly reduced blood pressure, arterial resistance and left ventricular end-diastolic pressure when compared to occluded vehicle-treated animals (group II). Administration of CGS 21680 at the highest dose also significantly increased cardiac output (28%) and heart rate (10%) in comparison to occluded vehicle-treated animals. In addition, the highest dose of CGS 21680 significantly reduced P_mcf (9%) and venous resistance (62%) in comparison to occluded vehicle-treated animals. Administration of CGS 21680 did not significantly affect +dP/dt when compared to occluded vehicle-treated animals.
5. The results from the present investigation indicate that occlusion of the coronary artery in rats results in a state of heart failure characterized by reduced arterial pressure and cardiac output, and increased venous resistance, P_mcf and left ventricular end-diastolic pressure. Administration of CGS 21680 to animals with acute heart failure resulted in increased cardiac output which was due to reduced venous resistance, as well as increased heart rate.