Critical independent regions in the VWF propeptide and mature VWF that enable normal VWF storage. (65/430)

Von Willebrand factor (VWF) is synthesized in endothelial cells, where it is stored in Weibel-Palade bodies. Administration of 1-desamino-8-D-arginine-vasopressin (DDAVP) to patients with type 1 von Willebrand disease and to healthy individuals causes a rapid increase in plasma VWF levels. This increase is the result of stimulated release of VWF from Weibel-Palade bodies in certain beds of endothelial cells. The VWF propeptide (VWFpp) targets VWF to storage granules through a noncovalent association. The nature of the VWFpp/VWF interaction was investigated by using cross-species differences in VWF storage. While canine VWFpp traffics to storage granules and facilitates the multimerization of human VWF, it does not direct human VWF to storage granules. Since storage takes place after furin cleavage, this defect appears to be due to the defective interaction of canine VWFpp and human VWF. To determine the regions within VWFpp and VWF important for this VWFpp/VWF association and costorage, a series of human-canine chimeric VWFpp and propeptide-deleted VWF (Deltapro) constructs were produced and expressed in AtT-20 cells. The intracellular localization of coexpressed proteins was examined by confocal microscopy. Two amino acids, 416 in VWFpp and 869 in the mature VWF molecule, were identified as being critical for the association and granular storage of VWF.  (+info)

Changes in von Willebrand factor-cleaving protease (ADAMTS13) activity after infusion of desmopressin. (66/430)

von Willebrand factor-cleaving protease (ADAMTS13) cleaves von Willebrand factor (VWF) and regulates its physiologic function. To investigate the relation between ADAMTS13 activity and VWF, we compared ADAMTS13 activity with the VWF-related parameters VWF antigen (VWF:Ag), VWF collagen-binding activity (VWF:CBA), VWF-propeptide, proVWF, and VWF multimeric composition in 10 healthy volunteers and 3 patients with type 1 von Willebrand disease before and after infusing 0.3 microg/kg desmopressin. The VWF-related parameters in the volunteers increased 60 minutes after start of infusion by 3.7-fold for VWF:Ag, 7.2-fold for propeptide, and 2.2-fold for VWF:CBA. Unusually large VWF multimers and traces of proVWF appeared. The ADAMTS13 activity decreased to about half the initial value. After 24 hours values returned to baseline. Patients with type 1 von Willebrand disease showed similar results. We conclude that the inverse correlation between ADAMTS13 and VWF-related parameters suggests a consumption of ADAMTS13 after the desmopressin-induced release of higher multimers of VWF.  (+info)

The effect of caffeine on renal epithelial cells from patients with autosomal dominant polycystic kidney disease. (67/430)

Autosomal dominant polycystic kidney disease (ADPKD) is a hereditary disorder characterized by the progressive enlargement of cysts derived from tubules. Tubule cell proliferation and chloride-dependent fluid accumulation, mechanisms underlying cyst expansion, are accelerated by adenosine 3':5'-cyclic monophosphate (cAMP). This study examined the extent to which caffeine may stimulate the production of cAMP by cyst epithelial cells, thereby adversely increasing proliferation and fluid secretion. Mural epithelial cells from ADPKD cysts and normal human kidney cortex cells (HKC) were cultured, and cAMP levels were determined in response to caffeine and receptor-mediated agonists linked to adenylyl cyclase. Caffeine, a methylxanthine, slightly increased basal levels of cAMP, as did other nonselective phosphodiesterase (PDE) inhibitors, 1-methyl-3- isobutyl xanthine and theophylline and rolipram, a specific PDE IV inhibitor. More importantly, clinically relevant concentrations of caffeine (10 to 50 micro M) potentiated the effects of desmopressin (DDAVP), prostaglandin E(2) (PGE(2)), and isoproterenol to increase cAMP levels in both ADPKD and HKC cells. By contrast, at concentrations that augmented the DDAVP response, caffeine attenuated cAMP accumulation by adenosine, implicating an action apart from the inhibition of PDE. Caffeine enhanced the effect of DDAVP to stimulate transepithelial short-circuit current of polarized ADPKD monolayers, reflecting an increase in chloride secretion. Caffeine potentiated the effect of DDAVP and PGE(2) to increase the levels of phosphorylated extracellular signal-regulated kinase (P-ERK). By contrast, P-ERK levels in HKC cells were not raised by increased intracellular concentrations of cAMP. It is concluded that PDE inhibition by caffeine increases the accumulation of cAMP, and through this mechanism activates the ERK pathway to cellular proliferation and increases transepithelial fluid secretion in ADPKD cystic epithelium. Caffeine is, therefore, a risk factor for the promotion of cyst enlargement in patients with ADPKD.  (+info)

Axial heterogeneity in basolateral AQP2 localization in rat kidney: effect of vasopressin. (68/430)

The purpose of the present study was to examine whether there is axial heterogeneity in the basolateral plasma membrane (BLM) localization of AQP2 and whether altered vasopressin action or medullary tonicity affects the BLM localization of AQP2. Immunocytochemistry and immunoelectron microscopy revealed AQP2 labeling of the BLM in connecting tubule (CNT) cells and inner medullary collecting duct (IMCD) principal cells in normal rats and vasopressin-deficient Brattleboro rats. In contrast there was little basolateral AQP2 labeling in cortical (CCD) and outer medullary collecting duct principal cells. Short-term desamino-Cys(1), (D)-Arg(8) vasopressin (dDAVP) treatment (2 h) of Brattleboro rats caused no increase in AQP2 labeling of the BLM. In contrast, long-term dDAVP treatment (6 days) of Brattleboro rats caused an increased BLM labeling in CNT, CCD, and IMCD. Treatment of normal rats with V(2)-receptor antagonist for 60 min caused retrieval of AQP2 from the apical plasma membrane. Moreover, AQP2 labeling of the BLM was unchanged in CNT and IMCD but increased in CCD. In conclusion, there is an axial heterogeneity in the subcellular localization of AQP2 with prominent AQP2 labeling of the BLM in CNT and IMCD. There was no increase in AQP2 labeling of the BLM in response to short-term dDAVP. Moreover, acute V(2)-receptor antagonist treatment did not cause retrieval of AQP2 from the BLM. In contrast, long-term dDAVP treatment caused a major increase in AQP2 expression in the BLM in CCD.  (+info)

Role of desmopressin in the treatment of a case of septic shock refractory to catecholamines. (69/430)

The authors describe a case of septic shock refractory to high-dose catecholamines after adequate volemic filling, rapidly corrected with the administration of desmopressin at a dose of 0.02 U/min. There are, in the literature, several cases of septic shock refractory to high-dose catecholamines successfully treated with arginine-vasopressin, a selective V1 agonist. This agent can potentially induce coronary vasoconstriction and presents a very difficult weaning, that imposes a slow reduction of the infusion amount. On the contrary, desmopressin does not present those adverse effects and is able to maintain a high renal blood flow, for its prevalent action on V2 instead of V1 receptors.  (+info)

Von Willebrand's disease in the year 2003: towards the complete identification of gene defects for correct diagnosis and treatment. (70/430)

BACKGROUND: Von Willebrand's disease (VWD) is an autosomally inherited bleeding disorder caused by a deficiency or abnormality of von Willebrand factor (VWF). VWF is a multimeric adhesive protein which plays an important role in primary hemostasis by promoting platelet adhesion to the subendothelium at sites of vascular injury and platelet-platelet interactions in high shear-rate conditions. It is also the carrier of factor VIII (FVIII), thus indirectly contributing to the coagulation process. VWD has a prevalence of about 1% in the general population, but the figure for clinically relevant cases is lower (about 100/million inhabitants). Bleeding manifestations are heterogeneous: mucosal bleeding is typical of all VWD cases but hemarthrosis and hematomas may also be present when FVIII levels are low. INFORMATION SOURCES: Most cases appear to have a partial quantitative deficiency of VWF (type 1 VWD) with variable bleeding tendency, whereas qualitative variants (type 2 VWD), due to a dysfunctional VWF, are clinically more homogeneous. Type 3 VWD is rare and the patients have a moderate to severe bleeding diathesis because of the virtual absence of VWF, and a recessive pattern of inheritance. The diagnosis of VWD, especially type I, may be difficult, because the laboratory phenotype is highly heterogeneous and is confounded by the fact that factors outside the VWF gene (e.g., blood group) influence VWF levels. An array of tests is usually required to characterize the VWD types of the disorder and establish the best treatment modality. CONCLUSIONS: The aim of treatment is to correct the dual defect of hemostasis, i.e. abnormal coagulation expressed by low levels of FVIII and abnormal platelet adhesion expressed by the prolonged bleeding time (BT). Desmopressin (DDAVP) is the treatment of choice for type 1 VWD because it corrects the FVIII/VWF levels and the prolonged BT in the majority of cases. In type 3 and in severe forms of type 1 and 2 VWD, DDAVP is not effective and for these patients plasma virally-inactivated concentrates containing FVIII and VWF are the mainstay of treatment. These concentrates are clinically effective and safe, although they do not always correct the BT.  (+info)

Vasopressin increases urinary albumin excretion in rats and humans: involvement of V2 receptors and the renin-angiotensin system. (71/430)

BACKGROUND: An increase in urinary albumin excretion (UAE) represents an early predictor of glomerular damage in diabetes mellitus (DM) and a risk factor for cardiovascular complications in hypertension. Vasopressin is elevated in DM and in some forms of hypertension. Previous studies in rats suggested that this hormone could play a role in the albuminuria observed in chronic renal failure or diabetic nephropathy, but no information is available concerning the mechanism of these effects and the possible influence of vasopressin on UAE in the healthy kidney. The present study was thus designed to evaluate whether vasopressin influences UAE in normal rats and humans, whether this effect is V(2)-receptor-dependent, and whether it is mediated by the renin-angiotensin system. METHODS: UAE was measured in normal Wistar rats and healthy humans, or in subjects with various forms of diabetes insipidus (DI), before and after acute or chronic infusion of the vasopressin V(2) receptor agonist dDAVP. Chronic dDAVP administration was also performed in normal Wistar rats previously submitted to either chronic angiotensin-converting enzyme inhibition (ACEI) or chronic blockade of AT1 receptors (ARB). RESULTS: In rats, acute or chronic dDAVP infusion increased UAE significantly and reversibly (4-fold and 6-fold, respectively). In healthy subjects, acute infusion of dDAVP tripled UAE (P<0.01) but did not change creatinine and beta(2)-microglobulin excretion, thus suggesting that the rise in UAE was due to an increased glomerular leakage of albumin. dDAVP also increased UAE in patients with central DI and in patients with hereditary nephrogenic DI bearing AQP2 mutations. However, UAE was not increased in patients with hereditary nephrogenic DI bearing mutations of the V(2) receptor. In rats, ACEI and ARB blunted the dDAVP-induced rise in UAE by 70% (P<0.05) and 50% (NS), respectively. CONCLUSIONS: The present studies reveal for the first time that vasopressin induces a marked increase in UAE in healthy rats and humans. This albuminuric effect seems to result from increased glomerular leakage, requires functional vasopressin V(2) receptors, and is, at least in part, mediated by the renin-angiotensin system. These results bring additional support for an involvement of vasopressin in the albuminuria observed in pathological states such as diabetes mellitus or hypertension.  (+info)

Comparative response of plasma VWF in dogs to up-regulation of VWF mRNA by interleukin-11 versus Weibel-Palade body release by desmopressin (DDAVP). (72/430)

Recombinant human interleukin-11 (rhIL-11), a glycoprotein 130 (gp130)-signaling cytokine approved for treatment of thrombocytopenia, also raises von Willebrand factor (VWF) and factor VIII (FVIII) by an unknown mechanism. Desmopressin (1-deamino-8-d-arginine vasopressin [DDAVP]) releases stored VWF and FVIII and is used for treatment of VWF and FVIII deficiencies. To compare the effect of these 2 agents, heterozygous von Willebrand disease (VWD) and normal dogs were treated with either rhIL-11 (50 microg/kg/d subcutaneously x 7 days) or DDAVP (5 microg/kg/d intravenously x 7 days). The rhIL-11 produced a gradual and sustained elevation of VWF and FVIII levels in both heterozygous VWD and normal dogs while DDAVP produced a rapid and unsustained increase. Importantly, rhIL-11 treatment produced a 2.5- to 11-fold increase in VWF mRNA in normal canine heart, aorta, and spleen but not in homozygous VWD dogs, thus identifying a mechanism for elevation of plasma VWF in vivo. Moreover, dogs pretreated with rhIL-11 retain a DDAVP-releasable pool of VWF and FVIII, suggesting that rhIL-11 does not significantly alter trafficking of these proteins to or from storage pools. The half-life of infused VWF is unchanged by rhIL-11 in homozygous VWD dogs. These results show that rhIL-11 and DDAVP raise plasma VWF by different mechanisms. Treatment with rhIL-11 with or without DDAVP may provide an alternative to plasma-derived products for some VWD and hemophilia A patients if it is shown safe in clinical trials.  (+info)