Natriuretic effect of adenosine A1-receptor blockade in rats

Background: Many effects of adenosine on renal function have been identified. The development of adenosine receptor blockers has made it possible to identify which of these effects are exerted by endogenous adenosine. At least four adenosine receptor subtypes, denoted A1, A2a, A2b, and A3 are currently known. In the present study the selective A1 receptor blocker 1,3-dipropyl-8[2-(5,6-epoxy) norbanyl] xanthine (CVT-117) was used to assess the effect of A1 activation by endogenous adenosine on renal function in rats. Methods: Clearance studies were performed before and after administration of 0.1 mg/kg and 0.8 mg/kg of CVT-117 in separate groups of rats and before and after administration of vehicle in time-control rats. Measurement of heart rate before and after administration of exogenous adenosine confirmed effective A1 receptor blockade. Results: At both the lower and higher doses, A1 receptor blockade with CVT-117 increased fractional sodium excretion and urine flow rate without altering GFR. The increase in sodium excretion following A1 blockade was not accompanied by increases in the excretion of phosphate or potassium. Conclusion: These results show that endogenous adenosine promotes sodium retention by activation of A1 receptors.     

Amelioration of cyclosporine nephrotoxicity by irbesartan, A selective AT1 receptor antagonist

Cyclosporine A (CsA), a fungal undecapeptide, is the most common immunosuppressive drug used in organ transplantation and autoimmune diseases. However, nephrotoxicity is the major adverse effect of CsA use. The molecular mechanisms of CsA nephrotoxicity are not well characterized, but more recent studies suggest an involvement of angiotensin II (ANG II) and reactive oxygen species in the development of cyclosporine nephrotoxicity. Induction of heat shock proteins (HSPs) is one of the best-described cellular responses to heat stress, hypoxia, and exposure to oxidants. HSPs have beneficial roles in protein processing and protection against cell injury. There is emerging evidence that ANG II induces oxidative stress in vitro and in vivo. This study was thus designed to investigate the role of Angiotensin II type I (AT1) receptor antagonist, irbesartan, on CsA-induced nephrotoxicity. Five groups of rats were employed in this study: group 1 served as control, group 2 rats were treated with CsA (20 mg kg(-1), subcutaneously for 21 days), and groups 3, 4, and 5 received CsA along with irbesartan (10, 25, and 50 mg kg(-1), perorally 24 hr before and 21 days concurrently), respectively. Renal function was assessed by measuring serum creatinine, blood urea nitrogen, creatinine, and urea clearance. The renal oxidative stress was measured by renal malondialdehyde levels, reduced glutathione levels, and enzymatic activity of catalase, glutathione reductase, and superoxide dismutase. Renal morphological alterations were assessed by histopathological examination. CsA administration for 21 days resulted in a marked renal oxidative stress and significantly deranged the renal functions as well as renal morphology. All these factors were significantly improved by irbesartan (50 mg kg(-1)) treatment. HSP72, HSP47, and HSP25 were clearly induced and expressed in CsA-treated animals. The induction and expression of HSP25 was markedly protected by treatment with irbesartan, whereas the induction and expression of HSP47 and HSP72 remained unaltered with the irbesartan treatment. These results clearly demonstrate the pivotal role of ANG II-induced oxidative stress and therapeutic potential of AT, receptor antagonist in ameliorating CsA-induced nephrotoxicity.     

Amelioration of cholinergic-induced pancreatitis with a selective cholecystokinin receptor antagonist

Acute edematous pancreatitis follows excessive cholinergic stimulation in patients exposed to anticholinesterase-containing insecticides. We describe the role of cholecystokinin and the benefits of cholecystokinin receptor blockade in this form of pancreatitis. A cholinergic mimetic (carbachol) was administered to rats weighing 300 to 350 g and produced a form of edematous pancreatitis that mimics that seen in humans. Animals received carbachol intraperitoneally, either alone (250 micrograms/kg of body weight) or with cholecystokinin-receptor antagonist devazepide (3 mg/kg of body weight) and were killed 4 hours later. Carbachol administration resulted in a 19% increase in pancreatic weight, a fourfold increase in serum amylase levels, and a 14-fold increase in serum lipase levels. Plasma cholecystokinin levels, however, were not altered. Devazepide administered prior to cholinergic hyperstimulation blocked pancreatic weight increase and reduced elevations in serum amylase levels twofold and lipase levels fourfold. Although cholecystokinin levels are not elevated in this model of pancreatitis, blockade of even low, background concentrations of this regulatory peptide is beneficial.     

Combined effects of vasopressin V2 receptor antagonist and loop diuretic in humans

AIMS: Patients with edematous diseases are generally treated with diuretics, but frequently present with hyponatremia associated with impaired water excretion. This study investigated the combined effects of vasopressin V2 receptor antagonist OPC-31260, an aquaretic, and furosemide, a saluretic, on free water excretion and serum sodium concentration (PNa). MATERIAL AND METHODS: The study was planned as an open-label, 4-period, 4-treatment, crossover study in 12 healthy subjects using single doses of placebo, furosemide 20 mg (F), OPC-31260 30 mg (O), and furosemide 20 mg plus OPC-31260 30 mg (O+F). RESULTS: OPC-31260 co-administered with furosemide induced an increase in PNa and serum osmolality (F: 281.6 +/- 0.7, O+F: 284.9 +/- 0.7 mOsm/kgH2O) as a result of an additive increase in maximal urine volume (F: 7.7 +/- 1.9, O: 6.8 4 0.5, O+F: 13.2 +/- 1.4 ml/min) with increased electrolyte-free water excretion (F: 0.35 +/- 0.15, O: 5.3 4 0.5, O+F: 4.8 +/- 0.5 ml/min) while maintaining sodium excretion (F: 731 +/- 110, O+F: 1,064 +/- 149 microEq/min). It was suggested that by the co-administration, the resulting decreased generation of free water in Henle's loop was canceled out by a decrease in back--diffusion of free water across the collecting ducts. CONCLUSIONS: The co-administration may be particularly effective in treating edema and hyponatremia in edematous diseases.     

Adenosine A1 receptor antagonist improves intradialytic hypotension

Intradialytic hypotension is a most frequent complication of hemodialysis and may contribute to cardiovascular events and high mortality. There is a hypothesis that an increase in adenosine generation during hemodialysis may cause vasodilation and a decrease in cardiac output, which results in systemic hypotension. We studied whether this can be blocked by an adenosine A1 receptor antagonist. We investigated the effects of an A1 antagonist, FK352, injection in 30 chronic hemodialysis patients with frequent intradialytic hypotension by a prospective, multicenter, double-blind placebo-controlled study for 4 weeks after 4 weeks of the observation period. Intradialytic hypotension was defined as systolic blood pressure (SBP) less than 110 mmHg, with SBP drop of more than 30 mmHg from the predialysis level. The efficacy of FK352 was primarily assessed by the reduction rate of dialysis hypotension between the FK352 and placebo groups. Incidence of emergency treatments caused by hypotension was evaluated. FK352 (50 mg, intravenous) or an equivalent placebo was injected into the dialysis circuit 1 h after starting dialysis. Blood pressure and heart rate were monitored every 30 min during dialysis. FK352 significantly improved intradialytic hypotension (P=0.046), in that the reduction rates of intradialytic hypotension in the FK352 and placebo groups were -12.8% (Q1 (first quantile), Q3 (third quantile): -27.5, -1.7), and +8.3% (Q1, Q3: -16.6, +16.7), respectively. The frequency of discontinuation of dialysis was significantly reduced by FK352. No apparent side effects were observed from treatment with FK352. In conclusion, the A1 antagonist FK352 may offer a novel therapeutic option for chronic dialysis patients associated with intradialytic hypotension.     

腺苷A1受体在全身麻醉中的作用研究进展

背景 由于腺苷在睡眠方面的作用与全身麻醉所产生的作用非常相似,近年来关于腺苷及其受体在全身麻醉过程作用的研究越来越多,但其机制尚无定论.目的 综述腺苷A1受体与全身麻醉的关系及在全身麻醉过程中可能的作用机制.内容 简述全身麻醉与腺苷A1受体在睡眠方面的相似之处以及全身麻醉相关的重要受体γ-氨基丁酸A型(γ-amino butyric acid A,GABAA)受体、N-甲基-D-天冬氨酸(N-methyl-D-aspartic acid,NMDA)受体与腺苷A1受体的关系,总结目前腺苷A1受体在全身麻醉中作用的研究结果.趋向 腺苷A1受体在全身麻醉中的作用机制尚不完全清楚,有待进一步的研究证实,研究腺苷A1受体和全身麻醉之间的关系对于临床麻醉工作及药物的研究应用有一定的指导意义.     

选择性、非选择性内皮素受体拮抗剂对创伤性休克大鼠的影响

目的 探讨选择性、非选择性内皮素(ET)受体拮抗剂对创伤性休克大鼠的影响。方法 采用后肢创伤法建立创伤性休克大鼠模型,随机分为休克组、休克+BQ-123组和休克+PD142893组,分别于创伤前、休克末、复苏后 1、3、5 h检测血浆内皮素及骨骼肌、肝脏、小肠的组织氧分压,监测血流动力学变化并记录存活时间。结果 3组大鼠休克末及复苏后备时间点血浆内皮素浓度及组织氧分压较伤前差异有显著性(P<0.05),休克+BQ-123组于复苏后 1、3 h血浆内皮素浓度显著低于休克组(P<0.05),复苏后肝脏、小肠的组织氧分压较休克组显著升高(P<0.05),其 12、24 h存活率同休克组比较差异均有显著性(P<0.05)。结论 创伤性休克后血浆内皮素浓度显著升高,选择性ETA受体拮抗剂BQ-123可显著改善创伤性休克大鼠内脏组织氧分压,延长存活时间。     

Modulating effect of a selective endothelin A receptor antagonist on pulmonary endothelin system protein expression in experimental diaphragmatic hernia

Background/Purpose

Previously, we reported that perinatal administration of atrasentan, a selective endothelin A receptor (ET_A) antagonist, provided a beneficial effect on the cardiopulmonary profile under short-term conditions in newborn lambs with surgically induced congenital diaphragmatic hernia (CDH). We hypothesized that changes in the hemodynamic profile that we observed at birth in treated animals could be influenced by pulmonary modulation of the endothelin (ET) system.

Methods

The effect of atrasentan on protein expression levels of ETs and ET receptors (ET_A and ET_B receptor) was investigated by immunohistochemistry in lung tissues of untreated control (n = 3), treated control (n = 6), untreated CDH (n = 6), and treated CDH newborn lambs (n = 8).

Results

Right lung tissue of treated control lambs showed significantly higher ET_A protein expression levels in both vascular adventitia and airway epithelia when compared with that of untreated control lambs (P < .05). In contrast, protein expression levels of ET_A and ET _B receptor were significantly lower in the vascular smooth muscle cells among other tissue subcompartments of the right lung of treated CDH newborn lambs vs CDH lambs (P < .02 and P = .005, respectively).

Conclusions

We speculate that rapid pulmonary modulation of ET system protein expression levels by atrasentan results from an indirect effect possibly dependent on ventilation and/or perfusion. In CDH groups, this could contribute to the beneficial effect of the treatment.     

Nonischaemic priapism associated with selective serotonin‐3 receptor antagonist

Priapism is a rare but severe urological emergency of erection of penis in the absence of physical and psychological sexual stimulation. Priapism is often idiopathic and is commonly associated with medications and underlying medical or traumatic causes. In this report, we present a case of a 70‐year‐old White Caucasian man who developed priapism after the administration of ondansetron, which is a selective serotonin type‐3 (5‐HT3) receptor antagonist. This case is unique, because, to date, there are only two presented cases in literature. The objective of this case report is to highlight the importance of recognising the possibility of priapism with ondansetron because this condition is not commonly seen in clinical practice to be associated with ondansetron and may go unrecognised. Also, potential pathophysiological mechanisms involved in the development of ondansetron‐induced priapism are presented.     

Renal tubule necrosis and apoptosis modulation by A1 adenosine receptor expression

We have shown that A1 adenosine receptors (A1ARs) are cytoprotective against renal tubular necrosis and apoptosis both in vivo and in vitro. To study the role of A1AR numbers on renal epithelial cell survival, we stably overexpressed the human A1 receptor in a porcine renal tubule cell line and utilized primary cultures of proximal tubules obtained from A1AR knockout mice. Receptor-overexpressing cells were protected against peroxide-induced necrosis and tumor necrosis factor-alpha/cycloheximide-induced apoptosis. Conversely, cultured proximal tubule cells from receptor knockout mice showed more necrotic and apoptotic cell loss than corresponding cells from wild-type mice. Overexpression of the receptor resulted in a significantly higher baseline expression of both total and phosphorylated heat-shock protein (HSP)27; the latter due to A1 receptor enhancement of p38 and AP2 mitogen-activated protein kinase activities. The resistance to cell death in the porcine cells was reversed by selective A1 receptor antagonism and by a selective inhibitor of HSP synthesis. Receptor activation in wild-type mice in vivo led to increased total and phosphorylated HSP27, whereas receptor knockout mice showed decreased baseline and adenosine-mediated HSP phosphorylation. These studies show that endogenous A1AR activation produces cytoprotective effects in renal proximal tubules by modulating HSP27 signaling pathways.     

Interleukin-1 receptors and receptor antagonist in haemodialysis

Background. Biological activity of interleukin-1 (IL-1) depends on the number and type of IL-1 receptors on target cells and on the amounts of its naturally occurring inhibitor, the IL-1 receptor antagonist (IL-1ra). Methods. Expression of IL-1 receptor was studied on the peripheral blood mononuclear cells of 20 end-stage renal-disease patients maintained by chronic haemodialysis by means of either polysuphone (10 patients) or cuprophane membranes (10 patients) and compared to that of normal controls. Plasma and cellular levels of IL-1ra and IL-1{beta} were also measured. Results. The proportion of monocytes expressing the IL-1 receptor was strikingly higher in haemodialysis patients than in the healthy population. This proportion further increased during haemodialysis with cuprophane but not with polysulphone. Expression of the IL-1 receptor on lymphocytes was very low in both controls and dialysed patients; in the latter there was no intradialytic variation. Plasma concentrations of IL-1{beta} and IL-1ra were elevated in haemodialysis patients and undetectable in controls. Whereas plasma IL-1{beta} decreased throughout haemodialysis, IL-1ra further increased, with no significant differences between the two membranes used. Total cellular IL-1{beta} and IL-1ra were also higher in the patient group than in the healthy controls. A further increase of both IL-1{beta} and IL-1ra was detected at the end of the haemodialysis session with any membrane. Conclusion. Monocytes of haemodialysis patients circulate in a state of activation, which makes them both producer and target of IL-1. Thus there is an autocrine upregulation of IL-1. Although IL-1ra levels are high, they are most likely to be expression of monocyte activation rather than represent effective inhibitors of IL-1 activity.     

A selective alpha1A-adrenoceptor antagonist inhibits detrusor overactivity in a rat model of benign prostatic hyperplasia

PURPOSE: Alpha(1)-adrenoceptor antagonists relax the obstructed prostatic urethra and suppress the irritative symptoms frequently observed in patients with benign prostatic hyperplasia. We investigated the effects of 3 alpha(1)-adrenoceptor antagonists on urodynamics in rats with hormone induced benign prostatic hyperplasia to determine which alpha(1)-adrenoceptor subtype selective antagonists would suppress irritative symptoms. MATERIALS AND METHODS: Rats were treated with testosterone and 17beta-estradiol by weekly intramuscular injections. After 4 weeks a pressure flow study was done and the effects of the alpha(1)-adrenoceptor antagonists KMD-3213 silodosin, tamsulosin and prazosin on urodynamics were compared. We especially investigated the involvement of the bladder and prostatic urethra to clarify the mechanism of detrusor overactivity expression. RESULTS: Hormone treatment induced benign prostatic hyperplasia and resulted in detrusor overactivity, as determined by cystometry. Baseline perfusion urethral pressure and the phenylephrine induced increase in it were significantly higher in rats with vs without benign prostatic hyperplasia. Cystometry in hormone treated female rats did not show detrusor overactivity. KMD-3213 decreased detrusor overactivity, similar to other alpha(1)-adrenoceptor antagonists. CONCLUSIONS: These results suggest that an excessive response to sympathetic nerve stimulation, which is mainly mediated via alpha(1A)-adrenoceptor, in the hypertrophied prostate gives rise to detrusor overactivity. Furthermore, the alpha(1A)-adrenoceptor selective antagonist KMD-3213 would be suitable for improving irritative symptoms in patients with benign prostatic hyperplasia.     

Protective effects of selective mineralocorticoid receptor antagonist against aortic aneurysm progression in a novel murine model

Background

The optimal medical management to delay the progression of aortic aneurysms has not been fully clarified, and the only standard treatment at present is antihypertensive therapy. Previous studies have shown beneficial effects of selective mineralocorticoid receptor (MR) antagonists on cardiovascular remodeling. The aim of the present study was to investigate the effect of a selective MR antagonist on aortic aneurysm progression.

Methods

Seven-week-old C57BL/6J male mice were administered with angiotensin II and β-aminopropionitrile for 4 weeks. The mice received either vehicle or eplerenone, a selective MR antagonist (100 mg/kg daily) every day by gavage, starting at 7 weeks of age. The production of inflammatory cytokines in cultures of high mobility group box-1–stimulated macrophages with or without a MR antagonist was also analyzed using an enzyme-linked immunosorbent assay.

Results

Although no differences were found in the peak systolic blood pressure between the experimental groups, the mice in the eplerenone group showed a significant reduction in aneurysm development. On histologic analysis, coarse and stretched elastic fibers were markedly improved in the aortic wall in the eplerenone group. Real-time polymerase chain reaction of both aortic wall and perivascular adipose tissue demonstrated the expression of tumor necrosis factor-α, interleukin-6, and matrix metalloproteinase-2 was significantly decreased in eplerenone group, and that of monocyte chemoattractant protein-1 in the aortic wall was also significantly decreased. Macrophage infiltration in the aortic wall and perivascular adipose tissue in the eplerenone group was also significantly decreased. The production of tumor necrosis factor-α and interleukin-6 in macrophage culture, which was stimulated by high mobility group box-1 and CpG oligodeoxynucleotides, was also significantly decreased in the eplerenone group.

Conclusions

Eprelenone suppressed aortic aneurysm progression through an anti-inflammatory effect. Thus, selective MR antagonists might be effective in preventing the progression of aortic aneurysms.     

Comparison of the effects of angiotensin II receptor antagonist monotherapy and combination therapy with a diuretic on cardiac function in spontaneously hypertensive rats

Objective

Losartan, an angiotensin II receptor blocker (ARB), has been reported to promote sodium excretion and show an enhanced antihypertensive effect when used in combination with hydrochlorothiazide (HCTZ). We investigated the effects of losartan monotherapy and combination therapy together with HCTZ on cardiac function in hypertensive rats using echocardiography.

Methods

Spontaneously hypertensive rats (n?=?21) fed on high-salt diet (8?% NaCl) for 13?weeks were randomly assigned to rats without medication (HS, n?=?7), those medicated with ARB (ARB, losartan 30?mg/kg/day, n?=?8), and those with ARB and HCTZ (ARB?+?HCTZ, losartan 30?mg/kg/day?+?HCTZ 10?mg/kg/day, n?=?6). Blood pressure measurements and echocardiography were performed at 13, 17, and 29?weeks of age. After the end of the protocol, the proportion of cardiac muscle fibrosis was measured histologically.

Results

In the HS group, blood pressure and left ventricular mass/body weight (LV mass/BW) increased, and % fractional shortening (%FS) and early diastolic mitral annular velocity (e??) decreased significantly with age. In the ARB group, although blood pressure and %FS were maintained, LV mass/BW increased with age as in the HS group, and e?? decreased. In the ARB?+?HCTZ group, blood pressure decreased and LV mass/BW, %FS, and e?? were maintained. The progression of myocardial fibrosis was clearly prevented in rats treated with ARB.

Conclusion

ARB was shown to inhibit systolic disorder and myocardial fibrosis in hypertensive rats. Combination therapy proved to be more effective than monotherapy and is also effective in inhibiting diastolic disorders.     

Impaired glucose tolerance in the absence of adenosine A1 receptor signaling

OBJECTIVE

The role of adenosine (ADO) in the regulation of glucose homeostasis is not clear. In the current study, we used A1-ADO receptor (A1AR)-deficient mice to investigate the role of ADO/A1AR signaling for glucose homeostasis.

RESEARCH DESIGN AND METHODS

After weaning, A1AR^−/− and wild-type mice received either a standard diet (12 kcal% fat) or high-fat diet (HFD; 45 kcal% fat). Body weight, fasting plasma glucose, plasma insulin, and intraperitoneal glucose tolerance tests were performed in 8-week-old mice and again after 12–20 weeks of subsequent observation. Body composition was quantified by magnetic resonance imaging and epididymal fat-pad weights. Glucose metabolism was investigated by hyperinsulinemic-euglycemic clamp studies. To describe pathophysiological mechanisms, adipokines and Akt phosphorylation were measured.

RESULTS

A1AR^−/− mice were significantly heavier than wild-type mice because of an increased fat mass. Fasting plasma glucose and insulin were significantly higher in A1AR^−/− mice after weaning and remained higher in adulthood. An intraperitoneal glucose challenge disclosed a significantly slower glucose clearance in A1AR^−/− mice. An HFD enhanced this phenotype in A1AR^−/− mice and unmasked a dysfunctional insulin secretory mechanism. Insulin sensitivity was significantly impaired in A1AR^−/− mice on the standard diet shortly after weaning. Clamp studies detected a significant decrease of net glucose uptake in A1AR^−/− mice and a reduced glucose uptake in muscle and white adipose tissue. Effects were not triggered by leptin deficiency but involved a decreased Akt phosphorylation.

CONCLUSIONS

ADO/A1AR signaling contributes importantly to insulin-controlled glucose homeostasis and insulin sensitivity in C57BL/6 mice and is involved in the metabolic regulation of adipose tissue.Adenosine (ADO), a purine nucleoside, is a ubiquitous product of ATP breakdown, with a large variety of regulatory functions. ADO effects are mediated by four receptors (AR): A1, A2a, A2b, and A3, each showing an organ-specific expression pattern and different half-maximal effective concentration (EC50), thus facilitating differential effects (1). ARs mediate downstream effects mostly via G-protein–coupled receptors that are either stimulatory (A2a and A2b) or inhibitory (A1 and A3) to adenylate cyclase. The resulting increase or decrease of cAMP induces downstream signaling by triggering phosphorylation activation of key enzymes (2).A role of the metabolic byproduct of ATP utilization, adenosine, in the regulation of glucose uptake and utilization makes physiological sense. Nevertheless, previous studies of the effect of ADO on glucose transport have yielded conflicting results in that insulin sensitivity and/or glucose uptake were reported as either decreased (3–6) or increased (7–9). The availability of mice with adenosine receptor deletions offers a new way to assess the role of a chronic reduction in ADO signaling on glucose tolerance. Recently, we discovered a nephropathic phenotype in an A1AR-deficient Akita hybrid mouse model of type 1 diabetes, suggesting a relevant role for A1AR signaling in maintaining glucose homeostasis (10). Another recent study showed that mice with A1AR deletion have a higher fat content with aging (11). Because of the well-established relationship between excess body weight and insulin resistance, we considered it possible that the phenotype of A1AR-deficient mice may include the development of glucose intolerance and insulin resistance. In the current study, we have therefore used A1AR-deficient mice to examine the hypothesis that ADO signaling via A1AR contributes to glucose homeostasis. Our main findings support this notion in that A1AR-deficient mice show a defect in glucose tolerance that seems to be a result of insulin resistance.