Early Conversion From Calcineurin Inhibitor- to Everolimus-Based Therapy Following Kidney Transplantation: Results of the Randomized ELEVATE Trial

In a 24-month, multicenter, open-label, randomized trial, 715 de novo kidney transplant recipients were randomized at 10-14 weeks to convert to everolimus (n = 359) or remain on standard calcineurin inhibitor (CNI) therapy (n = 356; 231 tacrolimus; 125 cyclosporine), all with mycophenolic acid and steroids. The primary endpoint, change in estimated glomerular filtration rate (eGFR) from randomization to month 12, was similar for everolimus versus CNI: mean (standard error) 0.3(1.5) mL/min/1.73² versus -1.5(1.5) mL/min/1.73² (p = 0.116). Biopsy-proven acute rejection (BPAR) at month 12 was more frequent under everolimus versus CNI overall (9.7% vs. 4.8%, p = 0.014) and versus tacrolimus-treated patients (2.6%, p < 0.001) but similar to cyclosporine-treated patients (8.8%, p = 0.755). Reporting on de novo donor-specific antibodies (DSA) was limited but suggested more frequent anti-HLA Class I DSA under everolimus. Change in left ventricular mass index was similar. Discontinuation due to adverse events was more frequent with everolimus (23.6%) versus CNI (8.4%). In conclusion, conversion to everolimus at 10-14 weeks posttransplant was associated with renal function similar to that with standard therapy overall. Rates of BPAR were low in all groups, but lower with tacrolimus than everolimus.

Prophylaxis of recurrent urinary tract infection after renal transplantation by cranberry juice and L-methionine

BACKGROUND

Recurrent urinary tract infections (UTIs) increase mortality and reduce graft survival after renal transplantation. Strategies to prevent recurrent UTIs include L-methionine, cranberry juice, and antibiotics. Data on the efficacy of cranberry and L-methionine, however, are controversial in the general population; there are few data in renal transplant recipients.

METHODS

We performed a retrospective analysis of 82 transplant recipients with recurrent UTIs, who underwent prophylaxis with cranberry juice (2 × 50 mL/d, n = 39, 47.6%), or L-methionine (3 × 500 mg/d, n = 25, 30.5%), or both modalities (n = 18, 21.9%). Thirty patients without prophylaxis served as controls. We analyzed symptoms, pyuria/nitrituria, and incidence of UTI events during 1 year before versus after initiation of prophylaxis.

RESULTS

Prophylaxis highly significantly decreased the annual UTI incidence by 58.3% (P < .001) in the study population with no change in the control group (P = .85); in addition, 53.7% of symptomatic patients reported relief of symptoms and pyuria/nitrituria disappeared in 42.4% of the dipstick-positive patients (P < .001 each). Cranberry reduced the annual number of UTI episodes by 63.9% from 3.6 ± 1.4 to 1.3 ± 1.3/year (P < .001) and L-methionine by 48.7% from 3.9 ± 1.8 to 2.0 ± 1.3/year (P < .001).

CONCLUSION

Cranberry juice and L-methionine successfully reduced the incidence of UTI after renal transplantation.

Intraoperative assessment of kidney allograft perfusion by laser-assisted indocyanine green fluorescence videography

BACKGROUND

Kidney allograft function crucially depends on the quality of organ perfusion. Duplex sonography, however, frequently reveals hypoperfused segments that remained undetectable to visual inspection intraoperatively. To date, no imaging system supplementing the surgeon's experience has achieved clinical acceptance. The present work examines whether laser-assisted indocyanine green (ICG) fluorescence-videography can be used as a safe and sensitive technique for the intraoperative assessment of renal allograft perfusion.

METHODS

Intraoperative assessment of organ perfusion by laser-assisted ICG fluorescence videography (IC-VIEW) was performed in 10 consecutive de novo renal transplantations. The IC-VIEW system allows the visualization of graft perfusion by the fluorescein dye ICG that emits infrared light after exposure to laser light.

RESULTS

Perfusion measurements were successful in all 10 transplant recipients. Fluorescence videography produced brilliant, sharply contrasted images of the organs, allowing the detection of even small perfusion deficits. Remarkably, this technique detected 1 large perfusion defect that had remained imperceptible to visual inspection. Repositioning of the graft led to a homogeneous overall perfusion. There were no complications with the ICG injection or the imaging device.

CONCLUSION

Laser-assisted ICG fluorescence videography is a feasible and safe technique for the intraoperative assessment of renal allograft perfusion.

A new oscillometric method for pulse wave analysis: comparison with a common tonometric method

In the European Society of Cardiology-European Society of Hypertension guidelines of the year 2007, the consequences of arterial stiffness and wave reflection on cardiovascular mortality have a major role. But the investigators claimed the poor availability of devices/methods providing easy and widely suitable measuring of arterial wall stiffness or their surrogates like augmentation index (AIx) or aortic systolic blood pressure (aSBP). The aim of this study was the validation of a novel method determining AIx and aSBP based on an oscillometric method using a common cuff (ARCSolver) against a validated tonometric system (SphygmoCor). aSBP and AIx measured with the SphygmoCor and ARCSolver method were compared for 302 subjects. The mean age was 56 years with an s.d. of 20 years. At least two iterations were performed in each session. This resulted in 749 measurements. For aSBP the mean difference was -0.1 mm Hg with an s.d. of 3.1 mm Hg. The mean difference for AIx was 1.2% with an s.d. of 7.9%. There was no significant difference in reproducibility of AIx for both methods. The variation estimate of inter- and intraobserver measurements was 6.3% for ARCSolver and 7.5% for SphygmoCor. The ARCSolver method is a novel method determining AIx and aSBP based on an oscillometric system with a cuff. The results agree with common accepted tonometric measurements. Its application is easy and for widespread use.

The impact of pulse pressure on the accuracy of wrist blood pressure measurement

There is an increasing number of wrist blood pressure measurement devices that successfully passed the validation procedures of the British Hypertension Society (BHS) and the European Society of Hypertension (ESH). It remains unknown, however, whether pulse pressure as a marker of arterial stiffness and vascular ageing affects the accuracy of these devices. An ESH protocol validated wrist device was compared with the upper arm mercury sphygmomanometry in a study population (33 patients, 99 measurements) including a relevant number of subjects with pulse pressure >50 mm Hg (84.8%) and isolated systolic hypertension (27.3%). Mean systolic bias was 10.2 mm Hg with 95% limits of agreement of -13.1 and 33.6 mm Hg, mean diastolic bias was 4.8 mm Hg with limits of agreement of -11.0 and 20.7 mm Hg. The impact of body mass index, age, systolic blood pressure and pulse pressure on the absolute value of blood pressure bias was tested by stepwise multiple regression analysis. The systolic bias significantly depended on pulse pressure, whereas there was no significant effect of the independent variables on the diastolic bias. Separate correlation analysis showed a significant correlation between pulse pressure and both absolute systolic bias (Pearson r=0.48, P<0.001) and relative systolic bias (systolic bias divided by systolic blood pressure, Pearson r=0.29, P=0.003). Even well-validated wrist blood pressure devices can show a clinically relevant bias in patients with elevated pulse pressure. Increased arterial stiffness may impair the accuracy of oscillometric blood pressure measurement at the wrist.

Paracrine stimulation of vascular smooth muscle proliferation by diadenosine polyphosphates released from proximal tubule epithelial cells

The purinergic receptor system plays an important role in the regulation of both vascular and tubular functions within the kidney; however, the release of purinergic agonists other than ATP by renal tissue is not known. In this investigation, we determine if kidney tissue is a source of diadenosine polyphosphates, which have high affinity for the P(2X) and P(2Y) receptors. Both diadenosine pentaphosphate and hexaphosphate were identified by matrix-assisted laser desorption ionization-mass spectrometry in extracts purified from both whole porcine kidney and from cloned cells of the LLC-PK1 cell line. Both polyphosphates in nanomolar concentrations were found to significantly stimulate the proliferation of vascular smooth muscle cells derived from rat thoracic aortas. The purinergic-receptor antagonist, suramin, did not significantly affect the growth-stimulatory properties of the polyphosphates. The growth stimulation of vascular smooth muscle cells by platelet-derived growth factor was potentiated by both diadenosine polyphosphates. We conclude that diadenosine polyphosphates are endogenous purinergic agonists of the kidney that have physiologic and pathophysiologic relevance. These epithelial cell metabolic products have vasoregulatory properties while linking the energy supply and tubular function.

Beta-blockers do not impair the cardiovascular benefits of endurance training in hypertensives

Aerobic physical exercise is broadly recommended as a helpful adjunct to obtain blood pressure control in hypertension. Beta-blockade interacts with heart rate, sympathetic tone, maximal workload and local lactate production. In the present randomized-controlled study, we compared the cardiovascular effects of an endurance training programme in elderly hypertensives with or without beta-blockers and developed a first approach to determine a lactate-based training heart rate in presence of beta-blockade. Fifty-two patients (23 with beta-blocker, 29 without beta-blocker) > or =60 years with systolic 24-h ambulatory blood pressure (ABP) > or =140 mm Hg and/or antihypertensive treatment were randomly assigned to sedentary activity or a heart-rate controlled 12-week treadmill exercise programme (lactate 2.0 mmol/l). In the exercise group, the training significantly decreased systolic and diastolic 24-h ABP, blood pressure on exertion (100 W) and increased endothelium-dependent vasodilation (flow-mediated vasodilation, FMD) and physical performance both in the presence and absence of beta-blockade (P<0.05 each). The extent of ABP reduction did not significantly differ in the presence or absence of beta-blockade (Delta systolic ABP 10.6+/-10.5 vs 10.6+/-8.8 mm Hg, Delta diastolic ABP 5.7+/-8.6 vs 5.8+/-4.0 mm Hg). Mean training heart rate was significantly lower in the patients on beta-blockers (97.2+/-7.7 vs 118.3+/-7.5/min, P<0.001). Lactate-based aerobic endurance training evokes comparable cardiovascular benefits in the presence and absence of beta-blockade including a marked improvement of endothelial function. In the present study, target training heart rate with beta-blockers is about 18% lower than without.

Sphingosine-1-phosphate and FTY720 as anti-atherosclerotic lipid compounds

All stages of atherosclerosis have been identified as a chronic vascular inflammatory disease. In the last few years there is increasing evidence that endogenous lysophospholipids such as sphingosine-1-phosphate (S1P) have potent anti-inflammatory properties. The S1P analogue FTY720 that has been developed as a potent, orally active, immunosuppressant in the field of transplantation and autoimmune disease has interesting effects on inflammatory processes in the arterial vessel wall. S1P targets five specific S1P receptors (S1P(1-5)), which are ubiquitously expressed. S1P(1-3) receptor expression is identified in arterial vessels. S1P and FTY720 show potent silencing effects on some vascular proinflammatory mechanisms in endothelial and vascular smooth muscle cells. In addition, the interaction of monocytes with the vessel wall is inhibited. As shown recently, FTY720 can effectively reduce the progression of atherosclerosis in apolipoprotein E-deficient mice having a high-cholesterol diet. It is not entirely clear which S1P receptor subtype is mainly involved in this process. However, it is currently speculated that the S1P(3) and probably the S1P(1) is involved in the anti-atherosclerotic effects of FTY720. This review summarizes the current knowledge about S1P- and FTY720-effects on mechanisms of vascular inflammatory disease. In addition S1P receptor subtypes are identified which might be interesting for molecular drug targeting.

Dermatopathic lymphadenopathy: a differential diagnosis of enlarged lymph nodes in uremic pruritus

BACKGROUND

In end-stage renal disease patients, the incidence of both infections and malignancies is increased leading to a higher incidence of peripheral lymphadenopathy. In the present work we describe a rare but probably underdiagnosed cause for enlarged lymph nodes in uremic patients.

PATIENT

A 43-year-old male patient was admitted to our hospital with inguinal lymphadenopathy and pruritus. He turned out to be uremic due to focal segmental glomerulosclerosis (creatinine 4.5 mg/dl, MDRD creatinine clearance 12 ml/min).

FINDINGS

Sonography revealed enlarged lymph nodes (up to 4 cm) with intact corticohilar border differentiation. After extirpation of an inguinal lymph node, histological examination established the diagnosis of dermatopathic lymphadenopathy. T cell lymphoma was excluded by PCR for T cell receptor-gamma rearrangements and subsequent GeneScan analysis. Intravenous fluid supplementation with subsequent decline of creatinine, UVB treatment, clemastine, and topical use of emollients led to a relief of the uremic pruritus and the lymph nodes' size normalized within 8 weeks.

CONCLUSION

Dermatopathic lymphadenopathy refers to the reactive condition seen in lymph nodes that drain areas with disruption of the skin integrity, e.g. due to scratch marks. The present case report describes dermatopathic lymphadenopathy as a harmless cause of enlarged lymph nodes in uremic pruritus for the first time. This entity should be considered in the differential diagnosis of peripheral lymphadenopathy of unknown origin in patients with renal failure.

Mesangial IgA deposition in minimal change nephrotic syndrome: coincidence of different entities or variant of minimal change disease?

BACKGROUND

Mesangial deposition of IgA (MCA) is a very rare finding in minimal change disease and has previously been considered a pure coincidence. In the U.S. and Europe only anecdotal case reports exist. To date, there has been no consensus on nomenclature and categorization of this entity. We describe 2 cases of MCA with analogue histological findings but relevant differences in clinical presentation, and we discuss the clinical implications of mesangial IgA deposition in minimal change nephrotic syndrome.

PATIENTS

A 47-year-old female was admitted to hospital with nephrotic syndrome, microscopic hematuria, arterial hypertension and slight impairment of renal function 3 weeks after an unspecific upper airway infection. A 42-year-old male presented with nephrotic syndrome, microscopic hematuria, normotension and normal renal function. Both of the nephrotic syndromes were steroid-responsive and steroid-dependent.

FINDINGS

The clinical presentation of the male patient was consistent with the features of minimal change glomerulopathy, whereas the female patient combined signs of minimal change disease and IgA nephropathy. Light microscopy revealed mesangial IgA immune deposits and slight mesangial hypercellularity. Electron microscopic studies of MCA patients disclose diffuse effacement of glomerular foot processes.

CONCLUSION

Our cases and a review of the literature indicate that the histological diagnosis of MCA may comprise different pathogenetic entities. From the clinical point of view, MCA has to be regarded as a minimal change nephrotic syndrome with symptomatic or asymptomatic mesangial IgA deposition. IgA deposition constitutes a risk factor for impairment of renal function and indicates a frequently relapsing course.

Tacrolimus in steroid-resistant and steroid-dependent nephrotic syndrome

BACKGROUND

Steroid resistance and steroid dependence constitute a major problem in the treatment of minimal-change disease and focal segmental glomerulosclerosis (FSGS). Cyclophosphamide and cyclosporine are well-established alternative immunomodulating agents, whereas data on FK 506 (tacrolimus) are rare.

METHODS

The present work provides data from 10 patients of an open, monocentric, non-randomized, prospective trial. Five patients with steroid-dependent minimal-change nephrotic syndrome, 1 patient with steroid-refractory minimal-change disease and 4 patients with steroid-refractory FSGS were started on tacrolimus at trough levels of 5 10 microg/l. In case of steroid-dependence, prednisolone was tapered off in presence oftacrolimus within one month.

RESULTS

Within 6 months, complete remission was achieved in 5 patients (50%) and partial remission in 4 patients (40%), yielding a final response rate of 90%. One patient was primarily resistent to tacrolimus (steroid-refractory minimal-change), another patient became secondarily resistant to tacrolimus after an initial remission (steroid-refractory FSGS). Average proteinuria significantly decreased by 77% from 9.5 +/- 1.4 - 2.2 +/- 1.1 g/day (p < 0.01). Serum protein significantly raised from 55.0 +/- 1.9 - 64.6 +/- 1.9 g/l (p < 0.01). Tacrolimus induced non-significant increases of blood glucose (4.9 +/- 0.1 - 5.1 +/- 0.2 mmol/l), systolic blood pressure (131.4 +/- 7.1 - 139.0 +/- 7.6 mmHg) and creatinine (93.2 +/- 13.9 103.2 +/- 15.3 mmol/l). Five patients have been tapered off tacrolimus so far, nephrotic syndrome relapsed in 4 of them (80%). Relapse occurred at tacrolimus levels between 2.6 and 6.9 ng/ml.

CONCLUSIONS

Our data suggest that tacrolimus may be a promising alternative to cyclosporine both in steroid-resistant and steroid-dependent nephrotic syndrome.

[New tendencies in combination antihypertensive therapy]

In the management of hypertension, the constant lowering of target pressures ever more frequently requires combination treatment in order to achieve the goals set. A combination of amlodipine and perindopril effectively lowered the blood pressure, and significantly reduced overall mortality, cardiovascular mortality, cardiovascular events and stroke risk in comparison with atenolol/bendroflumethiazide. In combination with both ACE inhibitors and AT1 blockers, diuretics reduced blood pressure more effectively that the respective components used alone. Now, however, the long-term use of diuretics is suspected of increasing the risk of terminal kidney failure and diabetes. This also means an enhanced probability of a cardiovascular event. In the ASCOT study, the combination of beta blocker and diuretic proved inferior to treatment with a calcium antagonist and ACE inhibitor. For the long-term application of diuretics as antihypertensive monotherapy, therefore, further comparative studies involving the latest antihypertensives are mandatory.

[Medical treatment of hypertension--what treatment for what patients?]

The antihypertensive agents of first choice include ACE-inhibitors, angiotensin receptor blockers, beta blockers, calcium antagonists and diuretic agents. For the selection of medicaments, the individual patient risk profile of decisive importance. In particular a metabolic syndrome, diabetes mellitus, disturbed renal function and/or a disturbed electrolyte household must be considered. For initial treatment monotherapy or a low-dose combination regime is suggested. If the response is inadequate, possible options include increasing the dose, changing the medicament, (sequential monotherapy) or, in the sense of stepped treatment, introduction of further combination drugs. Resistance to therapy should prompt consideration of a number of causes, in particular noncompliance on the part of the patient.

Increased plasma phenylacetic acid in patients with end-stage renal failure inhibits iNOS expression

NO prevents atherogenesis and inflammation in vessel walls by inhibition of cell proliferation and cytokine-induced endothelial expression of adhesion molecules and proinflammatory cytokines. Reduced NO production due to inhibition of either eNOS or iNOS may therefore reinforce atherosclerosis. Patients with end-stage renal failure show markedly increased mortality due to atherosclerosis. In the present study we tested the hypothesis that uremic toxins are responsible for reduced iNOS expression. LPS-induced iNOS expression in mononuclear leukocytes was studied using real-time PCR. The iNOS expression was blocked by addition of plasma from patients with end-stage renal failure, whereas plasma from healthy controls had no effect. Hemofiltrate obtained from patients with end-stage renal failure was fractionated by chromatographic methods. The chromatographic procedures revealed a homogenous fraction that inhibits iNOS expression. Using gas chromatography/mass spectrometry, this inhibitor was identified as phenylacetic acid. Authentic phenylacetic acid inhibited iNOS expression in a dose-dependent manner. In healthy control subjects, plasma concentrations were below the detection level, whereas patients with end-stage renal failure had a phenylacetic acid concentration of 3.49 +/- 0.33 mmol/l (n = 41). It is concluded that accumulation of phenylacetic acid in patients with end-stage renal failure inhibits iNOS expression. That mechanism may contribute to increased atherosclerosis and cardiovascular morbidity in patients with end-stage renal failure.

Captopril and quinapril reduce reactive oxygen species

BACKGROUND

Angiotensin-converting enzyme inhibitors may affect reactive oxygen species in humans in vitro and in vivo. In the present study we evaluated whether angiotensin-converting enzyme inhibitors may affect NAD(P)H oxidase activity.

MATERIALS AND METHODS

The production of reactive oxygen species was measured spectrophotometrically in mononuclear leukocytes using the fluorescent dye, dichlorofluorescein diacetate. The effects of quinaprilat, captopril, enalaprilat and lisinopril on phorbol myristate acetate-induced reactive oxygen species generation were investigated in vitro. The effects of quinaprilat, captopril, enalaprilat and lisinopril on the NAD(P)H oxidase activity of the mononuclear leukocytes were measured photometrically. In addition, reactive oxygen species were measured before and 4 h after oral administration of quinapril.

RESULTS

In vitro, the addition of quinaprilat (72 +/- 6% of control; mean +/- SEM; n= 19; P < 0.001) and captopril (48 +/- 2% of control; n= 19; P < 0.001) significantly reduced the phorbol-12-myristate-13-acetate-induced reactive oxygen species generation by the mononuclear leukocytes, whereas enalaprilat and lisinopril showed no effect. The effect of captopril on phorbol-12-myristate-13-acetate-induced reactive oxygen species generation in vitro was concentration-dependent. Quinaprilat and captopril significantly inhibited the NAD(P)H oxidase activity. After the oral administration of 10 mg of quinapril the phorbol-12-myristate-13-acetate-induced reactive oxygen species generation by the mononuclear leukocytes was significantly decreased from 1981 +/- 292% to 988 +/- 141% (n = 14; P < 0.01).

CONCLUSION

Quinapril and captopril decrease the production of reactive oxygen species.

Selective agonism of group I P2X receptors by dinucleotides dependent on a single adenine moiety

We have investigated the activity of naturally occurring high-performance liquid chromatography-purified diadenosine polyphosphates (Ap(n)A, n = 5-6), adenosine polyphospho guanosines (Ap(n)G, n = 5-6), and diguanosine polyphosphates (Gp(n)G, n = 5-6) under voltage-clamp conditions at recombinant rat P2X1-4 purinoceptor subtypes expressed in Xenopus laevis oocytes. At rP2X1 and rP2X3 receptors, Ap(n)As and Ap(n)Gs evoked concentration-dependent inward currents. Gp(n)Gs were not active at these receptors. At rP2X2 and rP2X4 receptors, dinucleotides did not show significant activity. For the rP2X1 receptor, Ap(n)As and Ap(n)Gs were partial agonists; for the P2X3 receptor, only Ap5G was full agonist, whereas the other tested substances were partial agonists. The rank order of potency at rP2X1 was ATP > or = Ap6A > or = Ap5A > or = Ap6G > or = Ap5G, and rank order of efficacy was ATP > or = Ap5A > or = Ap6A > Ap5G > Ap6G, whereas at rP2X3 the rank order of potency was ATP > Ap5G > or = Ap5A > or = Ap6A > or = Ap6G and the rank order of efficacy was ATP approximately Ap5G > or = Ap5A approximately Ap6A > or = Ap6G. For rP2X1 and rP2X3 it is evident that receptor agonism depended on the presence of at least one adenine moiety in the dinucleotide, while the presence of a guanine moiety had a significant impact and decreased agonist efficacy. The data suggest that naturally occurring Ap(n)As and Ap(n)Gs may play an important physiological role in different human tissues and systems by activating group I P2X receptors.

Efficacy and tolerability of angiotensin II type 1 receptor antagonists in dialysis patients using AN69 dialysis membranes

AIMS AND METHODS

Our aim was to evaluate the antihypertensive efficacy and tolerability of angiotensin II type 1 (AT1) receptor antagonists. Valsartan or candesartan cilexetil was administered to 11 dialysis patients with elevated blood pressure. The patients (6 male, 5 female; mean age +/- SD 61+/-11 years) were on regular bicarbonate hemodialysis three times weekly for more than 3 months using acrylonitrile and sodium methallyl sulfonate copolymer (AN69) dialysis membranes.

RESULTS

Within 252 days after administration of the AT1 receptor antagonists the systolic blood pressure was significantly reduced from 161+/-13 to 130+/-12 mmHg (p<0.001), whereas the diastolic blood pressure did not change significantly (76+/-8 vs. 71+/-8 mmHg; p>0.05). In addition, heart rate (75+/-7 vs. 80+/-8/min), body weight, and laboratory variables (hemoglobin, creatinine, blood urea nitrogen, serum potassium, serum sodium, serum calcium, and total protein) showed no significant changes. During 1,188 hemodialysis sessions using AN69 membranes, no hypersensitivity reactions occurred after administration of AT1 receptor antagonists.

CONCLUSION

The results indicate that once-daily administration of AT1 receptor antagonists efficiently reduces the systolic blood pressure in hemodialysis patients.

Increased vascular growth in hemodialysis patients induced by platelet-derived diadenosine polyphosphates

BACKGROUND

Enhanced vascular smooth muscle cell (VSMC) growth is one hallmark of atherosclerosis. One mechanism responsible for stimulating arterial smooth muscle cell growth is the release of growth factors from platelets aggregating at endothelial lesions. Since in end-stage renal failure (ESRF) atherogenesis is markedly accelerated, the release of VSMC growth factors on aggregation of platelets from hemodialysis patients, ESRF patients in the predialysis stage, and healthy subjects was examined.

METHODS

Platelets were activated by thrombin, and the supernatant was tested for growth stimulation in VSMCs from rat aorta. The cell proliferation rate was determined by [(3)H]-thymidine incorporation in VSMCs. The diadenosine polyphosphate (Ap(n)A with N = 3 to 6) content in the supernatant and in intact platelets was determined using a chromatographic assay established on the basis of affinity- and reversed-phase chromatographic methods.

RESULTS

The thrombin-activated platelet supernatant from hemodialysis patients (N = 15) increased the [(3)H]-thymidine incorporation rate in VSMC s in comparison to the supernatant of healthy control subjects (N = 17, counts/supernatant of 10(6) stimulated platelets +/- SEM, 604 +/- 71 vs. 364 +/- 45, P < 0.05). The addition of the selective P2-receptor blocker pyridoxal-phosphate-6-azophenyl-2,4-disulfonic acid to supernatants inhibited the stimulatory effects of Ap(n)A on the growth of vascular smooth muscle cells (219 +/- 53 vs. 156 +/- 71 counts/supernatant of 106 stimulated platelets +/- SEM). The Ap(n)A (N = 3 to 6) amount of thrombin-activated platelet supernatants from hemodialysis patients was significantly higher than in platelets from 10 healthy control subjects (Ap(3)A, 119 +/- 32 vs. 12 +/- 3; Ap(4)A, 154 +/- 59 vs. 43 +/- 20; Ap(5)A, 39 +/- 14 vs. 13 +/- 6; Ap(6)A, 42 +/- 19 vs. 2 +/- 1 fg/platelet +/- SEM, each P < 0.05, N = 10). The intracellular Ap(n)A (N = 3 to 6) amount of intact platelets from hemodialysis patients (N = 61) was significantly higher than that from healthy control subjects [N = 30, Ap(n)A amount (fg/platelet +/- SEM): Ap(3)A, 366 +/- 68 vs. 14.7 +/- 1; Ap(4)A, 336 +/- 48 vs. 19 +/- 2; Ap(5)A, 227 +/- 35 vs. 10 +/- 1; Ap(6)A, 141 +/- 45 vs. 4 +/- 1; each P < 0.01].

CONCLUSIONS

The increased amount of dinucleoside polyphosphate in platelets from hemodialysis patients may be an important additional atherogenic factor.

Characterization of p-hydroxy-hippuric acid as an inhibitor of Ca2+-ATPase in end-stage renal failure

Characterization of p-hydroxy-hippuric acid as an inhibitor of Ca2+-ATPase in end-stage renal failure. In patients with end-stage renal failure (ESRF), disturbances of Ca2+ metabolism are common. Besides hormonal changes, inhibition of cellular Ca2+-ATPase was postulated to contribute to uremic toxicity. We purified a potent inhibitor of the Ca2+-ATPase from the ultrafiltrate of patients with ESRF by multiple steps of high-performance liquid chromatography to homogeneity, and identified the isolated inhibitor by mass spectrometric methods as p-hydroxy-hippuric acid. The enzyme used for the Ca2+-ATPase assay system was isolated from red blood cells by cross-flow filtration. The activity of the Ca2+-ATPase was measured spectrophotometrically as the difference in hydrolysis of adenosine 5'-triphosphate (ATP) in the presence and absence of Ca2+ with different concentrations of ATP and p-hydroxyhippuric acid. The Ca2+-ATPase was found to be inhibited by p-hydroxy-hippuric acid at a concentration above 11.7 micromol/L. p-Hydroxyhippuric acid inhibited the erythrocyte Ca2+-ATPase by reducing Vmax and increasing the Km value. The EC50 (log mol/L; mean +/- SEM) for p-hydroxy-hippuric acid was calculated as 4.82 +/- 0.14. In conclusion, p-hydroxy-hippuric acid may play a role in disturbed Ca2+ metabolism in end-stage renal failure.

CoenzymeA glutathione disulfide is a potent modulator of angiotensin II-induced vasoconstriction

CoenzymeA glutathione disulfide (CoASSG) has recently been isolated from bovine adrenal glands and is assumed to play an important role in blood pressure (BP) control. We used the isolated perfused rat kidney to investigate the modulating effects of CoASSG on angiotensin II (AngII)-induced vasoconstriction. Permanent perfusion with CoASSG (1 micromol/L) for 60 min induced a significant (P < .05) shift to the left in the dose-response curve for AngII (about 3.1-fold), whereas the dose-response curve for norepinephrine (NE) was unaffected. During continuous perfusion with 1 micromol/L CoASSG, the repetitive application of 10 pmol AngII significantly increased its vasoconstriction by 170% +/- 14% (P < .05) and 235% +/- 50% (P < .05) for 60 and 120 min, respectively. The potentiation of AngII by permanent perfusion with CoASSG is dose- and time-dependent and shows a plateau at 120 min. Glutathione, oxidized coenzymeA, and coenzymeA (each 1 micromol/L) are not able to enhance the vasoconstriction induced by AngII. We conclude that CoASSG is able to potentiate the vasoactive properties of AngII, and that CoASSG might play an important role in BP regulation via modulating effects of AngII.

The critical role of adenosine and guanosine in the affinity of dinucleoside polyphosphates to P(2X)-receptors in the isolated perfused rat kidney

1. The activation of P(2x)-receptors in the rat renal vasculature by dinucleoside polyphosphates with variable phosphate group chain length (Xp(n)X; X=Adenin (A) /Guanin (G), n=4 - 6) was studied by measuring their effects on perfusion pressure of the isolated perfused rat kidney at constant flow in an open circuit. 2. Like Ap(4)A, Ap(5)A and Ap(6)A the dinucleoside polyphosphates Ap(4)G, Ap(5)G and Ap(6)G exerted a vasoconstriction which could be blocked by suramin and pyridoxal-phosphate-6-azophenyl-2; 4-disulphonic acid (PPADS). 3. Gp(4)G, Gp(5)G and Gp(6)G showed only very weak vasoconstriction at high doses. 4. Ap(6)A and alpha, beta-meATP could not be blocked by the selective P(2x1)-receptor antagonisten NF023 (30 microM), whereas Ap(4)A, Ap(4)G, Ap(5)A, Ap(5)G and Ap(6)G were partially blocked by NF023. 5. Inhibition of endothelial NO-synthase by N(omega)-nitro-L-arginine methyl ester (L-NAME) did not affect vasoconstrictions induced by dinucleosidepolyphosphates. 6. P(2x)-receptor can only be activated if at least one adenosine moiety is present in the molecule. 7. Ap(n)G show a weaker vasoconstrictive action than corresponding Ap(n)A, concluding that two adenosine moieties enhance the P(2x)-receptor binding and activation. 8. Xp(n)X containing five phosphate groups show the most pronounced vasoconstrictive effect whereas four phosphate groups show the less effect, therefore the number of phosphate groups critically changes receptor affinity. 9. Additional experiments using permanent perfusion with alpha, beta-methylene ATP (alpha,beta-meATP) and the selective P(2x1)-receptor antagonist NF023 showed that the newly discovered human dinucleoside polyphosphates activated the vascular P(2x1)-receptor and an recently identified new P(2x)-receptor subtype. 10. The differential effects of dinucleoside polyphosphates allow a fine tuning of local perfusion via composition of Xp(n)Xs.

Isolation and characterization of coenzyme A glutathione disulfide as a parathyroid-derived vasoconstrictive factor

BACKGROUND

Coenzyme A glutathione disulfide (CoA-SSG) was recently isolated from bovine adrenal glands and was shown to be a renal vasoconstrictor. The identification of CoA-SSG in human parathyroid glands and its action on cultured vascular smooth muscle cells (VSMCs) are described here.

METHODS AND RESULTS

After purification to homogeneity by several chromatographic steps, CoA-SSG was identified by matrix-assisted laser desorption/ionization mass spectrometry and enzymatic analysis. The dose-dependent growth-stimulating effect of CoA-SSG on VSMCs, measured by the [(3)H]thymidine method, is characterized by a threshold of 10(-)(8) mol/L and a maximum effect of 10 micromol/L, increasing VSMC proliferation 254+/-21% above control. A dose of 10 micromol/L methylmalonyl-CoA and 10 micromol/L CoA increased the rate of proliferation of VSMCs only by 178+/-43% and 50+/-42% above control, respectively. Glutathione has no proliferative effect on VSMCs. The growth-stimulating effect of CoA-SSG (1 micromol/L) was decreased by the antagonists 3,7-dimethyl-1-propargylxanthine (DMPX; 11 micromol/L) (38% compared with CoA-SSG without antagonist) and pyridoxal-phosphate-6-azophenyl-2,4-disulfonic acid (PPADS; 10 micromol/L) (48% compared with CoA-SSG without antagonist; each P:<0. 05 versus control), indicating that the effect is mediated partly via A(2) and partly via P(2)Y(1) and/or P(2)Y(4) receptor.

CONCLUSIONS

CoA-SSG may play a regulatory role in VSMC growth as a progression factor and thereby could play an important role in development of hypertension.

Increased sodium-proton antiporter activity in patients with obstructive sleep apnoea

Cytosolic pH (pH(i)) and the activity of the sodium-proton antiporter (Na(+)/H(+) antiporter) were measured in lymphocytes from 22 patients with obstructive sleep apnoea and from 24 age-matched healthy subjects (Controls). The cellular Na(+)/H(+) antiporter was measured spectrophotometrically using a pH-sensitive fluorescent dye after intracellular acidification using sodium propionate. Resting pHi was similar in lymphocytes from patients with obstructive sleep apnoea and from controls (7.36 +/- 0.20, n=22; vs. 7.35 +/- 0.19, n=24; mean +/- SD). The Na(+)/H(+) antiporter activity was significantly higher in patients with obstructive sleep apnoea than in controls (11.87 +/- 3.26 x 10(-3) pH(i)/s vs. 4.38 +/- 1.40 x 10(-3) pH(i)/s; P < 0. 0001). The apparent affinity of the Na+/H+ antiporter was not significantly different between the groups (6.90 +/- 0.23 vs. 6.87 +/- 0.20). In patients with obstructive sleep apnoea the activity of the Na(+)/H(+) antiporter remained stable during the night. The activity of the Na(+)/H(+) antiporter was 13.49 +/- 4.80 x 10(-3) pH(i)/s at 20.00 and 13.26 +/- 6.13 x 10(-3) pH(i)/s at 02.00. From the present results it is concluded that an increased cellular Na(+)/H(+) antiporter activity may be a genetic marker for patients who are predisposed to obstructive sleep apnoea.

Prevention of radiographic-contrast-agent-induced reductions in renal function by acetylcysteine

BACKGROUND

Radiographic contrast agents can cause a reduction in renal function that may be due to reactive oxygen species. Whether the reduction can be prevented by the administration of antioxidants is unknown.

METHODS

We prospectively studied 83 patients with chronic renal insufficiency (mean [+/-SD] serum creatinine concentration, 2.4+/-1.3 mg per deciliter [216+/-116 micromol per liter]) who were undergoing computed tomography with a nonionic, low-osmolality contrast agent. Patients were randomly assigned either to receive the antioxidant acetylcysteine (600 mg orally twice daily) and 0.45 percent saline intravenously, before and after administration of the contrast agent, or to receive placebo and saline.

RESULTS

Ten of the 83 patients (12 percent) had an increase of at least 0.5 mg per deciliter (44 micromol per liter) in the serum creatinine concentration 48 hours after administration of the contrast agent: 1 of the 41 patients in the acetylcysteine group (2 percent) and 9 of the 42 patients in the control group (21 percent; P=0.01; relative risk, 0.1; 95 percent confidence interval, 0.02 to 0.9). In the acetylcysteine group, the mean serum creatinine concentration decreased significantly (P<0.001), from 2.5+/-1.3 to 2.1+/-1.3 mg per deciliter (220+/-118 to 186+/-112 micromol per liter) 48 hours after the administration of the contrast medium, whereas in the control group, the mean serum creatinine concentration increased nonsignificantly (P=0.18), from 2.4+/-1.3 to 2.6+/-1.5 mg per deciliter (212+/-114 to 226+/-133 micromol per liter) (P<0.001 for the comparison between groups).

CONCLUSIONS

Prophylactic oral administration of the antioxidant acetylcysteine, along with hydration, prevents the reduction in renal function induced by contrast agents in patients with chronic renal insufficiency.

[Progressive renal failure. Why blood pressure must now be monitored]

Hypertension alone can lead to chronic nephrosclerosis and in addition promote the progressive worsening of renal function in various forms of renal disease, such as diabetic nephropathy, glomerular nephritis or interstitial nephritis. Thus, the treatment of chronic renal disease associated with reduced excretory function, requires not only general measures and a low-protein diet, but also intensified anti-hypertension treatment with diuretics or beta blockers. In a number of studies, progression or renal insufficiency has been shown to be slowed in particular through the use of angiotensin-converting enzyme inhibitors in patients with chronic renal failure.

Effect of dexamethasone on the lymphocytic Na+/H+ antiporter activity

OBJECTIVE

The effects of short-term administration of dexamethasone on sodium/proton antiporter (Na+/H+ antiporter) in human lymphocytes were investigated in vitro.

METHODS

Cytosolic pHi in lymphocytes was measured spectrophotometrically using the pH-sensitive fluorescent dye 2'-7'-bis-carboxyethyl-5(6)-carboxyfluorescein at 530 nm with excitation wavelengths of 440 and 530 nm. The Na+/H+ antiporter activity was determined after intracellular acidification using 100 mmol/l propionic acid.

RESULTS

The addition of 1 micromol/l dexamethasone significantly reduced cytosolic pHi from 7.44+/-0.03 to 7.25+/-0.05 (mean +/- SEM; P<0.01). Incubation with dexamethasone for 40 min significantly reduced the Na+/ H+ antiporter activity from (9.19+/-0.61)x10(-3) pHi/s (n = 22) to (7.23+/-0.49)x10(-3) pHi/s (n = 22; P<0.01). The effect of dexamethasone was time and concentration dependent The apparent affinity of the Na+/H+ antiporter was not significantly different in the absence or presence of dexamethasone. The inhibition of the Na+/H+ antiporter by dexamethasone was abolished in the presence of the glucocorticoid receptor blocker, mifepristone.

CONCLUSION

Dexamethasone directly inhibits the Na+/H+ antiporter using a receptor-dependent pathway. This effect may be important for pharmacological side effects such as glucocorticoid-induced hypertension.

Identification and characterization of P(1), P(7)-Di(adenosine-5')-heptaphosphate from human platelets

Diadenosine pentaphosphate and diadenosine hexaphosphate have been isolated in human platelets and have been postulated to play an important role in the control of vascular tone. Here we describe the isolation and identification of diadenosine heptaphosphate from human platelets. Dinucleoside polyphosphates were concentrated by affinity chromatography from a nucleotide-containing fraction from deproteinated human platelets. Dinucleoside polyphosphates were purified by anion-exchange and reversed phase high performance liquid chromatography to homogeneity. Analysis of one of these fractions with matrix-assisted laser desorption/ionization mass spectrometry revealed a molecular mass of 1076.4 (1077.4 = [M + H](+)) Da. UV spectroscopic analysis of this fraction showed the spectrum of an adenosine derivative. Comparison of the postsource decay matrix-assisted laser desorption/ionization mass spectrum of the fraction minus that of diadenosine heptaphosphate (Ap(7)A) demonstrated that the isolated substance was identical to Ap(7)A. The identity of the retention times of the authentic and the isolated compound confirmed this result. Enzymatic analysis demonstrated an interconnection of the phosphate groups with the adenosines in the 5'-positions of the riboses. With thrombin-induced platelet aggregation, Ap(7)A is released from the platelets into the extracellular space. The vasoconstrictive action of Ap(7)A on the vasculature of the isolated perfused rat kidney Ap(7)A was slightly less than that of Ap(6)A. The threshold of the vasoconstrictive action of Ap(7)A was 10(-5) mol/liter. The vasoconstrictive effect was abolished by suramin and pyridoxal phosphate 6-azophenyl-2', 4'-disulfonic acid, suggesting an activation of P(2x) receptors. Furthermore, Ap(7)A inhibits ADP-induced platelet aggregation. Thus, the potent vasoconstrictor Ap(7)A derived from human platelets, like other diadenosine polyphosphates, may play a role in the regulation of vascular tone and hemostasis.

Regulation of the Na+/H+ antiporter in patients with mild chronic renal failure: effect of glucose

BACKGROUND

The aim of this study was to determine the glucose-dependent regulation of the sodium-proton-antiporter (Na+/H+ antiporter) in patients with mild chronic renal failure (CRF).

METHODS

We measured plasma glucose concentrations, plasma insulin concentrations, plasma C peptide concentrations, arterial blood pressure, cytosolic pH (pHi), cellular Na+/H+ antiporter activity, and cytosolic sodium concentration ([Na+]i) in 19 patients with CRF and 41 age-matched healthy control subjects (control) during a standardized oral glucose tolerance test. Intracellular pHi, [Na+]i, and Na+/H+ antiporter activity was measured in lymphocytes using fluorescent dye techniques.

RESULTS

Under resting conditions, the pHi was significantly lower, whereas the Na+/H+ antiporter activity was significantly higher in CRF patients compared with controls (each P < 0.0001). The oral administration of 100 g glucose significantly increased the Na+/H+ antiporter activity in CRF patients from 13.35 +/- 1.26 x 10-3 pHi/second to 16.44 +/- 1.37 x 10-3 pHi/second after one hour and to 14.06 +/- 1.36 x 10-3 pHi/second after two hours (mean +/- SEM, P = 0.008 by Friedmans's two-way analysis of variance). In controls, the administration of 100 g glucose significantly increased the Na+/H+ antiporter activity from 4.23 +/- 0.20 x 10-3 pHi/second to 6.00 +/- 0.56 x 10-3 pHi/second after one hour and to 6.65 +/- 0.64 x 10-3 pHi/second after two hours (P = 0.0003). The glucose-induced enhancement of the Na+/H+ antiporter activity was more pronounced in CRF patients compared with controls (P = 0.011). Resting [Na+]i was not significantly different between the two groups.

CONCLUSIONS

CRF patients show an intracellular acidosis leading to an increased Na+/H+ antiporter activity. In addition, high glucose levels exaggerate the differences in Na+/H+ antiporter activity already present between cells from patients with mild CRF and those from control subjects.

Evidence for two different P2X-receptors mediating vasoconstriction of Ap5A and Ap6A in the isolated perfused rat kidney

The activation of various P2-receptor subtypes in rat renal vasculature by P1, P5-diadenosine pentaphosphate (ApsA) and P1, P6-diadenosine hexaphosphate (Ap6A) were studied by measuring their effects on perfusion pressure during continuous perfusion in a rat isolated perfused kidney. Permanent perfusion with Ap5A and Ap6A elicited both a transient and sustained vasoconstriction with both vasoconstrictions to be different: the transient vasoconstriction can be elicited with concentrations > or = 10 nM, whereas the sustained vasoconstriction is observed with concentrations > or = 1 nM. ApsA and Ap6A act via the same receptors as alpha,beta-methylene ATP (alpha,beta-meATP). The rank order of potency for transient vasconstriction was alpha,beta-meATP = ApsA>Ap6A>B,gamma-meATP, and for sustained vasoconstriction alpha,beta-meATP = Ap5A > beta,gamma-meATP > or = Ap6A. Suramin, a non-selective P2-receptor antagonist, and pyridoxal-phosphate-6-azophenyl-2;4-disulphonic acid (PPADS) a highly selective P2X-receptor antagonist antagonized both the transient and the sustained vasoconstriction. Taken together the results of the agonist profile of Ap5A and Ap6A and comparing its findings to literature it can be demonstrated that the transient but not the sustained vasoconstriction is mediated via the P2X1-receptor which is present in rat renal vasculature. It is demonstrated that the agonist profile of the sustained vasoconstriction induced by ApsA and Ap6A does not fit to any currently known P2X- or P2Y-receptor subtype. We conclude a yet unidentified P2X-receptor or chimeric P2X-receptor may contribute to the effects on rat renal vasculature produced by Ap5A and Ap6A and which may play an important role in glomerular perfusion pressure and blood pressure control.

High-performance liquid chromatographic assay of the diadenosine polyphosphates in human platelets

Diadenosine pentaphosphate (Ap5A) and diadenosine hexaphosphate (Ap6A) were recently identified in human platelets and were shown to be important modulators of cardiovascular function. Here we describe an HPLC assay for quantitating Ap3A, Ap4A, Ap5A, and Ap6A contents in human platelets simultaneously. Di(1,N6-ethenoadenosine) hexaphosphate was used as internal standard. The extraction procedure consists of (a) deproteinization, (b) selective concentration of the diadenosine polyphosphates with a boronate affinity chromatography, and (c) desalting prior to the HPLC analysis. The assay was validated by PSD-MALDI-mass spectrometry and by addition of authentic diadenosine polyphosphate to platelet samples. The assay was carried out by an ion-pair reversed-phase perfusion chromatography. In platelets from human blood the following amounts of diadenosine polyphosphates were determined: Ap3A, 192.5 +/- 151.0 nM; Ap4A, 223.8 +/- 172.3 nM; Ap5A, 100.2 +/- 81.1 nM; Ap6A, 32.0 +/- 19.6 nM (mean +/- SD, n = 105). The described assay can be used with less than 20 ml blood and allows quantitation of the diadenosine polyphosphates in the picomole range.

Mediation of the vasoactive properties of diadenosine tetraphosphate via various purinoceptors

OBJECTIVE AND METHODS

The vasoactive properties of P1,P4-diadenosine tetraphosphate (Ap4A) were studied by measuring the effects of perfusion pressure of a rat isolated perfused kidney.

RESULTS

The vasoconstrictive response to Ap4A was mediated to a large extent to a P2X receptor which could be shown by inhibition with pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid tetrasodium. The remaining vasoconstriction of Ap4A could be blocked by a 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective A1 receptor antagonist In raised tone preparation Ap4A evoked vasodilation when P2 receptors were blocked by suramin. The dilation was not mediated by a P2Y receptor as the effect could not be blocked by suramin.

CONCLUSION

Ap4A induces vasoconstriction via A1 and P2X receptors and vasodilatation via an unidentified receptor which is not a P2Y receptor. Ap4A may play an important role in kidney perfusion and, thus, in blood-pressure control.

Activation of Na+, H+ exchanger produces vasoconstriction of renal resistance vessels

To evaluate the influence of the sodium/proton exchanger (Na+,H+ exchanger) on the constriction of rat resistance vessels and on the iliac artery, the isometric vasoconstrictions of renal resistance vessels and strips from iliac artery derived from Wistar-Kyoto rats were measured using a vessel myograph. The Na+,H+ exchanger was activated by intracellular acidification using propionic acid. Cytosolic pH (pHi) and cytosolic free sodium concentration ([Na+]i) in vascular smooth muscle cells were measured using the fluorescent dye technique. The activation of the Na+,H+ exchanger increased the [Na+]i by 12.4 +/- 1.3 mmol/L (n = 8). The activation of the Na+,H+ exchanger caused a contractile response of the renal resistance vessels (increase of tension, 1.5 +/- 0.1 x 10(-3) N; n = 13) and of the rat iliac artery (increase of tension, 7.5 +/- 0.8 x 10(-3) N; n = 5). The contractile response after activation of the Na+,H+ exchanger was significantly inhibited in the absence of external sodium or in the presence of amiloride, confirming the involvement of the Na+,H+ exchanger. The contractile response after activation of the Na+,H+ exchanger was significantly reduced in the absence of external calcium, after inhibition of calcium channels by nifedipine, and in the presence of an intracellular calcium antagonist 8-(diethylamino-)-octyl-3,4,5-trimethoxybenzoate (TMB-8), indicating that the activation of the Na+,H+ exchanger consecutively caused transplasma membrane calcium influx. On the other hand, the inhibition of the Na+,Ca2+ exchanger by NiCl2 significantly increased the vasoconstriction of renal resistance vessels after activation of the Na+,H+ exchanger. The activation of the Na+,H+ exchanger produces vasoconstriction by an increased cytosolic sodium concentration, inhibition of the Na+,Ca2+ exchanger, and activation of transplasma membrane calcium influx through potential dependent calcium channels.

Adenosine(5') oligophospho-(5') guanosines and guanosine(5') oligophospho-(5') guanosines in human platelets

We isolated and identified nucleoside(5') oligophospho-(5') nucleosides containing adenosine and guanosine (ApnG; n = 3-6) as well as diguanosine polyphosphates (GpnG; n = 3-6) in human platelets. For identification, UV spectrometry, matrix-assisted laser desorption/ionization, postsource decay matrix-assisted laser desorption/ionization mass spectrometry, and enzymatic cleavage experiments were used. The adenosine(5') oligophospho-(5') guanosines act as vasoconstrictors and growth factors. The diguanosine polyphosphates are potent modulators of growth in vascular smooth muscle cells, but do not affect vascular tone.

Diadenosine polyphosphates' action on calcium and vessel contraction

The effects of the endogenous, platelet-derived vasoactive compounds, diadenosine tetraphosphate (AP4A), diadenosine pentaphosphate (AP5A), and diadenosine hexaphosphate (AP6A) on the vasoconstriction of isolated rat renal resistance vessels and rat aortic strips were measured using a vessel myograph. In addition, the effects of AP4A, AP5A, and AP6A on the cytosolic free calcium concentration ([Ca2+]i) were evaluated in cultured rat vascular smooth muscle cells (VSMC) using the fluorescent dye technique. Diadenosine polyphosphates dose-dependently increased the force of renal resistance vessels and isolated aortic strips. The administration of 10 mumol/L AP4A, AP5A, or AP6A significantly increased the force of isolated renal resistance vessels by 3.48+/-0.43 mN (n = 8), 2.14+/-0.40 mN (n = 12), or 2.70+/-0.31 mN (n = 11, each P < .01 compared with resting tension), respectively. The administration of 10 micromol/L AP4A, AP5A, or AP6A significantly increased the force of isolated aortic strips by 2.45+/-0.97 mNewton (n = 10), 2.70+/- 0.30 mN (n = 6), or 1.48+/-0.20 mN (each P < .01 compared with resting tension), respectively. The administration of 10 micromol/L AP4A, AP5A, or AP6A significantly increased [Ca2+]i in VSMC to a peak concentration of 314+/-60 nmol/L (n = 6), 247+/-25 nmol/L (n = 15), or 332+/-100 nmol/L (n = 5), respectively (each P < .01 compared with resting value). Both the diadenosine polyphosphate-induced vasoconstriction and [Ca2+]i increase was significantly reduced in the absence of extracellular calcium or after administration of a specific inhibitor of P2 purinoceptors. It is concluded that diadenosine polyphosphates increase [Ca2+]i and hence cause vessel constriction.