[The treatment of hypertension in the elderly : can it be done safely?]. / Enjeux et limites du traitement de l'hypertension artérielle chez la personne très âgée.

The treatment of arterial hypertension is important for the prevention of stroke and heart failure even in very old hypertensive patients, but represents a challenge in terms of safety and quality of life. Confirmation of the diagnosis with 24-hour ambulatory blood pressure (BP) monitoring or BP monitoring at home is important. A systolic BP of 150 mmHg (135-140 mmHg with out-of-office measures) is an acceptable cut-off value for both the diagnosis of hypertension and as a target for treatment. The fear of drug-induced orthostatic hypotension is only rarely a reason not to treat. However, in the context of co-morbidities, the risk of other side effects is considerable. Blood pressure may decrease over time, reducing the requirements for anti-hypertensive therapy. Cautious drug prescription, avoiding exceedingly intensive treatments plans, is important for treatment adequacy and safety.

[How to prevent severe hypoglycemia in older patients with type 2 diabetes]. / Hypoglycémie sévère chez le patient diabétique de type 2 âgé: quelle prévention?

Severe hypoglycemia is a feared complication of treatment in older diabetic patients (> 75 years) and a limiting factor for good glycemic control. Its real incidence is not well studied and probably underestimated. Cognitive impairment, malnutrition and/or cachexia, polypharmacy and a recent hospitalization are risk factors for severe hypoglycemia specific for older patients. Cognitive impairment screening can identify patients unable to manage their treatment. Simplification of treatment and/or transferring its execution to relatives must then be considered. Prevention also involves the detection of malnutrition and comorbidities, Age-adjusted therapeutic targets (HbA1c 7-8%) are important to avoid an exceedingly strict glycemic control. However, giving up on good glycemic control is not an adequate prevention strategy in itself.

The high prevalence of malnutrition in elderly diabetic patients: implications for anti-diabetic drug treatments.

BACKGROUND: Type 2 diabetes usually occurs in the context of obesity and associated insulin resistance. Current treatment recommendations are based on lifestyle modifications and incremental drug therapy. However, this approach could lead to inappropriate priorities upon ageing, when diabetes may be compounded by malnutrition and reduced insulin resistance. METHODS: We prospectively evaluated glycaemic and nutritional parameters in 146 consecutive diabetic patients (age 82.5 +/- 7.3 years, mean +/- sd) admitted to our geriatric service. We also implemented nutritional support therapy and a drug therapy adjustment protocol. Oral hypoglycaemic agent withdrawal was attempted in cases of good glycaemic control (HbA(1c) < 7.5% (<47 mmol/mol) or fasting blood glucose < 7.5 mmol/l). RESULTS: Mean BMI and HbA(1c) were 29.6 +/- 7.1 kg/m(2) and 6.9 +/- 1.2% (52 +/- 9 mmol/mol), respectively. Of the patients, 51.4% were taking 1-3 oral hypoglycaemic agents, 30.8% were on insulin and 9.6% on were on insulin and oral hypoglycaemic therapy. Low Mini Nutritional Assessment scores and serum marker levels indicated a high prevalence of malnutrition and/or chronic disease, even in obese patients. Mini Nutritional Assessment scores were positively associated with HbA(1c) values. Among patients treated by oral hypoglycaemic agents, complete drug withdrawal was achieved in 65.8%, much more often than new treatments were added (P = 0.002). Glycaemic control did not worsen after approximately 30 days, despite in-hospital nutritional therapy. Successful oral hypoglycaemic therapy withdrawal was associated with lower Mini Nutritional Assessment scores. CONCLUSIONS: Malnutrition is highly prevalent in elderly diabetic inpatients and, paradoxically, contributes to 'good' glycaemic control. Malnutrition should be screened for in these patients and, when present, should prompt a revision in diet and drug therapy. In particular, the possibility of reducing unnecessary drug therapy should be considered.

Cardiometabolic determinants of mortality in a geriatric population: is there a "reverse metabolic syndrome"?

AIMS: Diabetes or insulin resistance, overweight, arterial hypertension, and dyslipidaemia are recognized risk factors for cardiovascular (CV) disease. However, their predictive value and hierarchy in elderly subjects remain uncertain. METHODS: We investigated the impact of cardiometabolic risk factors on mortality in a prospective cohort study of 331 elderly high-risk subjects (mean age+/-SD: 85+/-7 years). RESULTS: Two-year total mortality was predicted by age, diabetes, low BMI, low diastolic blood pressure (DBP), low total and HDL cholesterol, and previous CV events. The effect of diabetes was explained by previous CV events. In non-diabetic subjects, mortality was predicted by high insulin sensitivity, determined by HOMA-IR and QUICKI indices. In multivariate analyses, the strongest mortality predictors were low BMI, low HDL cholesterol and previous myocardial infarction. Albumin, a marker of malnutrition, was associated with blood pressure, total and HDL cholesterol, and HOMA-IR. The inflammation marker CRP was associated with low total and HDL cholesterol, and high HOMA-IR. CONCLUSION: In very old patients, low BMI, low DBP, low total and HDL cholesterol, and high insulin sensitivity predict total mortality, indicating a "reverse metabolic syndrome" that is probably attributable to malnutrition and/or chronic disorders. These inverse associations limit the relevance of conventional risk factors. Previous CV events and HDL cholesterol remain strong predictors of mortality. Future studies should determine if and when the prevention and treatment of malnutrition in the elderly should be incorporated into conventional CV prevention.

A call to incorporate the prevention and treatment of geriatric disorders in the management of diabetes in the elderly.

The prevalence of type 2 diabetes increases with age. However, the management of diabetes in the elderly has received surprisingly little attention. Diabetes in the elderly is associated with a high risk of geriatric syndromes including malnutrition and sarcopenia, functional impairments, falls and fractures, incontinence, depression and dementia. Tight glycaemic control for the prevention of vascular complications is often of limited value in the elderly. However, glycaemic control and non-pharmacological therapy may prevent diabetes symptoms and delay geriatric syndromes. The prevention, screening and treatment of both conventional diabetic complications and geriatric syndromes should be integrated in a management plan to optimize the patients' overall health status and quality of life.

Vasopressin-induced von Willebrand factor secretion from endothelial cells involves V2 receptors and cAMP.

Vasopressin and its analogue 1-deamino-8-D-arginine vasopressin (DDAVP) are known to raise plasma von Willebrand factor (vWF) levels. DDAVP is used as a hemostatic agent for the treatment of von Willebrand's disease. However, its cellular mechanisms of action have not been elucidated. DDAVP, a specific agonist for the vasopressin V2 receptor (V2R), exerts its antidiuretic effect via a rise in cAMP in kidney collecting ducts. We tested the hypothesis that DDAVP induces vWF secretion by binding to V2R and activating cAMP-mediated signaling in endothelial cells. vWF secretion from human umbilical vein endothelial cells (HUVECs) can be mediated by cAMP, but DDAVP is ineffective, presumably due to the absence of V2R. We report that DDAVP stimulates vWF secretion in a cAMP-dependent manner in HUVECs after transfection of the V2R. In addition, vasopressin and DDAVP induce vWF secretion in human lung microvascular endothelial cells (HMVEC-L). These cells (but not HUVECs) express endogenous V2R, as shown by RT-PCR. Vasopressin-induced vWF secretion is mimicked by DDAVP and inhibited by the selective V2R antagonist SR121463B. It is mediated by cAMP, since it is inhibited by the protein kinase A inhibitor Rp-8CPT-cAMPS. These results indicate that vasopressin induces cAMP-mediated vWF secretion by a direct effect on endothelial cells. They also demonstrate functional expression of V2R in endothelial cells, and provide a cellular mechanism for the hemostatic effects of DDAVP.

The tetraspanin CD63/lamp3 cycles between endocytic and secretory compartments in human endothelial cells.

In the present study, we show that in human endothelial cells the tetraspanin CD63/lamp3 distributes predominantly to the internal membranes of multivesicular-multilamellar late endosomes, which contain the unique lipid lysobisphosphatidic acid. Some CD63/lamp3 is also present in Weibel-Palade bodies, the characteristic secretory organelle of these cells. We find that CD63/lamp3 molecules can be transported from late endosomes to Weibel-Palade bodies and thus that CD63/lamp3 cycles between endocytic and biosynthetic compartments; however, movement of CD63/lamp3 is much slower than that of P-selectin, which is known to cycle between plasma membrane and Weibel-Palade bodies. When cells are treated with U18666A, a drug that mimics the Niemann-Pick type C syndrome, both proteins accumulate in late endosomes and fail to reach Weibel-Palade bodies efficiently, suggesting that P-selectin, like CD63/lamp3, cycles via late endosomes. Our data suggest that CD63/lamp3 partitions preferentially within late endosome internal membranes, thus causing its accumulation, and that this mechanism contributes to CD63/lamp3 retention in late endosomes; however, our data also indicate that the protein can eventually escape from these internal membranes and recycle toward Weibel-Palade bodies to be reused. Our observations thus uncover the existence of a selective trafficking route from late endosomes to Weibel-Palade bodies.

von Willebrand factor, endothelial dysfunction, and cardiovascular disease.

von Willebrand factor (VWF), a glycoprotein involved in arterial thrombus formation, is released into the circulation by secretion from endothelial cells. Plasma VWF levels are determined by genetic factors including ABO blood groups and VWF mutations, and by non-genetic factors including aging, impaired nitric oxide production, inflammation, free radical production and diabetes. Plasma VWF levels have been proposed as a risk factor for cardiovascular events. Although they are only weakly associated with the risk of coronary heart disease (CHD) in the general population, they are a more promising CHD risk factor in high-risk populations with previous cardiovascular events, diabetes or old age. However, is it still unclear whether VWF levels directly determine the rate and severity of arterial thrombus formation or whether they merely reflect alteration in other endothelial functions. The future status of VWF levels as a cardiovascular risk factor depends on additional studies on the genetic determinants of both VWF levels and cardiovascular outcomes. Further studies on VWF levels as a predictor of the risk of stroke (rather than CHD) in elderly or other high-risk population are also promising. Such studies could lead to the clinical use of plasma VWF levels to refine the estimation of the cardiovascular risk and of the expected benefit of antithrombotic agents.

Dopamine modulates von Willebrand factor secretion in endothelial cells via D2-D4 receptors.

OBJECTIVE: von Willebrand factor (VWF) is acutely released from endothelial cells in response to numerous calcium-raising agents (e.g. thrombin, histamine) and cAMP-raising agents (e.g. epinephrine, adenosine, vasopressin). In contrast, very few inhibitors of endothelial VWF secretion have been described. The neurotransmitter dopamine is a modulator of exocytosis in several endocrine cells, and is possibly involved in the regulation of several endothelial cell functions. We therefore investigated the effect of dopamine on endothelial VWF secretion. RESULTS: Dopamine, D2/D3- and D4-specific agonists inhibited histamine- but not thrombin-induced VWF secretion. Expression of dopamine D2, D3 and D4 receptors was demonstrated by reverse transcription polymerase chain reaction (RT-PCR) in both human aortic (HAEC) and umbilical vein (HUVEC) endothelial cells. D2-D4 agonists did not inhibit histamine-induced rise in [Ca(2+)](i): they inhibited histamine-induced secretion even in the absence of extracellular calcium. Thus, the dopamine effects are not mediated by [Ca(2+)](i)-dependent signalling. D2/D3- and D4-specific agonists inhibited neither the rise in cAMP nor VWF secretion in response to epinephrine and adenosine, arguing against an effect on cAMP-mediated signalling. D1 and D5 receptors were not detected in HAEC or HUVEC by RT-PCR, and the D1/D5-specific agonist SKF 38 393 failed to modulate VWF secretion, arguing against a role for these receptors in endothelial exocytosis. CONCLUSIONS: Dopamine inhibits histamine-induced endothelial exocytosis by activating D2-D4 receptor, via a mechanism distinct from [Ca(2+)](i)-or cAMP-mediated signaling. In contrast, D1 and D5 receptors are not functionally expressed in cultured endothelial cells. Dopamine agonists may be useful as inhibitors of endothelial activation in inflammation and cardiovascular disease.

Insulinemia and leptinemia in geriatric patients: markers of the metabolic syndrome or of undernutrition?

The metabolic syndrome (MS) describes a cluster of metabolic disturbances including type 2 diabetes and/or insulin resistance, hypertension, dyslipidemia and obesity, which predict a high risk of cardiovascular disorders. The associated hyperinsulinemia and hyperleptinemia may contribute to the cardiovascular risk. However, the operational value of the MS in elderly patients is questionable. We therefore investigated the prevalence and significance of the MS in geriatric care. In a survey of 98 consecutive admissions of diabetic patients, <40% had a MS; this is a low value compared to younger diabetic adults, due to a low prevalence of obesity and dyslipidemia. We found a high prevalence of low BMI (<20 kg/m2), hypoalbuminemia and low total cholesterol levels, suggesting that the MS may be modified by undernutrition. The interplay between the MS and undernutrition was further studied in 30 non-diabetic patients. Both leptinemia and insulin resistance indexes (HOMA-IR and QUICKI) were strongly associated with BMI and body fat (measured by Bioelectrical impedance Analysis). BMI, leptinemia and insulin resistance indexes were associated with the Mini Nutritional Assessment (MNA) score. Thus, undernutrition is associated with low leptin and insulin levels and may obscure the association of these parameters with cardiovascular risk. In conclusion, the MS has a low prevalence in our population of elderly diabetic patients, and is of questionable prognostic value. It can be oveshadowed by undernutrition, which is associated with low body weight, leptinemia and insulin resistance indexes. Prevention of undernutrition and/or adjustment to its consequences should receive higher priority in the care of elderly diabetic patients.

[When can the treatment of isolated systolic hypertension be avoided?]. / Hypertension artérielle systolique isolée chez la personne âgée: faut-il toujours traiter?

The treatment of isolated systolic hypertension (ISH) in the elderly reduces the cardiovascular (CV) risk, in particular in patients with diabetes or previous CV events. However, in the very old (> 80-85 years) the treatment of ISH may increase global mortality, although it still decreases the risk of stroke. The benefits of treatment on the risk of dementia remain uncertain. To verify the indication for therapy, the diagnosis of ISH should be confirmed by ambulatory blood pressure monitoring. Since the absolute benefit of treatment is related to its duration, a limited life expectancy may restrict the real impact of treatment. The advantages and limitations of anti-hypertensive therapy in the elderly should be discussed individually, respecting the patient's autonomy.

Malnutrition in Very Old Hospitalized Patients: A New Etiologic Factor of Anemia?

BACKGROUND: Anemia and malnutrition are highly prevalent, frequently concomitant and associated with negative outcomes and mortality in the elderly. OBJECTIVES: To evaluate the association between these two entities, and test the hypothesis that protein-energy deficit could be etiology of anemia. DESIGN: Prospective case-control study. SETTING: Geriatric and Rehabilitation Hospital, Geneva University Hospitals, Switzerland. PARTICIPANTS: 392 patients (mean age 84.8 years old, 68.6% female). MAIN OUTCOME MEASURES: Hematological (hemoglobin (Hb)), chemical (iron work up, cyanocobalamin, folates, renal function, C-Reactive Protein (CRP)) and nutrition (albumin, prealbumin) parameters, and mini nutritional assessment short form (MNA-SF). RESULTS: The prevalence of anemia (defined as Hb<120 g/l) was 39.3%. Anemic patients were more frequently malnourished or at risk of malnutrition according to the MNA-SF (p=0.047), with lower serum albumin (p <0.001) and prealbumin (p <0.001) levels. Thirty-eight percent of these patients had multiple causes and 14.3% had no cause found for anemia. Among the latter 90.9% of patients with unexplained anemia had albumin levels lower than 35g/l. After exclusion of iron,vitamin B12 and folic acid deficits, anemic patients had lower albumin (p<0.001) and prealbumin (p 0.007) levels. Albumin level explained 84.5% of the variance in anemia. In multivariate analysis albumin levels remain associated with Hb only in anemic patients, explaining 6.4% of Hb variance (adj R2) and 14.7% (adj R2) after excluding inflammatory parameters (CRP>10). CONCLUSIONS: Albumin levels are strongly associated with anemia in the elderly. Screening for undernutrition should be included in anemia assessment in those patients. Further prospective studies are warranted in order to explore the effect of protein and energy supplementation on hemoglobin level.

Regulated von Willebrand factor (vWf) secretion is restored by pro-vWf expression in a transfectable endothelial cell line.

Von Willebrand factor (vWf) is a glycoprotein involved in primary hemostasis and synthesized in endothelial cells (EC). vWf is stored in secretory granules specific for EC called Weibel-Palade bodies (WPb). Studies on the molecular mechanisms of vWf storage and acute release are hampered by the limitations of the available endothelial cell culture models. We created a suitable model by stable transfection of the vWf-negative ECV304 endothelial cell line with pro-vWf cDNA. Pro-vWf was normally cleaved to mature vWf and stored in WPb. Acute vWf release occurred in response to the calcium ionophore A23187. Thus, vWf expression is sufficient to restore functional secretory granules in ECV304 cells. We used this model to study the role of WPb in the storage of tissue-type plasminogen activator (t-PA), a key fibrinolytic enzyme that is acutely released by EC, but whose intracellular storage compartment is still a matter of debate. We observed that restoration of WPb in ECV304 cells results in the targeting of t-PA to these storage granules.

Major lower limb amputations in the elderly observed over ten years: the role of diabetes and peripheral arterial disease.

BACKGROUND: Major amputation is a dreaded event with high mortality and morbidity. However, few studies have investigated the epidemiology of amputation in the elderly over time, in the face of evolving management and prevention efforts. METHODS: We undertook a retrospective study to determine the incidence rate, etiology and prognosis of major lower limb amputations (transtibial or higher) in elderly patients (> 65 years). Cases were identified over a 10-year period in the Geneva (Switzerland) area, where all amputations are performed in a single center and reliable demographic data are available. RESULTS: The rate of amputation varied from 1.8 to 11.4/10000 patients/year, increasing with age and male gender. Diabetes was present in 48% patients, and conferred a 10 times higher risk of amputation. Severe peripheral arterial disease (PAD) was present in > 94% patients. The prognosis remains poor, 47% patients had died after two years and only 53% patients could be equipped with a prosthetic limb. Over 10 years we found a progressive increase in age at amputation; this encouraging increase was mostly accounted for by diabetic patients (> 6 months per year). CONCLUSIONS: The rate of amputation observed among elderly patients was low. Neither the rate nor the prognosis improved over the decade studied. However, the age at amputation increased by > 6 months/year, particularly in diabetic amputees, suggesting that current management successfully delays amputation. Amputations were almost exclusively performed for severe PAD. Further reduction in the rate of amputation will require progress in the prevention and management of PAD.

Effect of glycemic control on the overnight dexamethasone suppression test in patients with diabetes mellitus.

Because many of the clinical features associated with Cushing's syndrome are frequently found in patients with diabetes mellitus, diabetic patients are often evaluated for Cushing's syndrome. The initial test for Cushing's syndrome is the 1 mg overnight dexamethasone suppression test (DST), but its value as a screening test in diabetic subjects, especially those with poor glycemic control, has been questioned. To address this issue, an overnight DST was administered to 100 subjects with diabetes. Only 7 patients failed to suppress their plasma cortisol to less than 140 nmol/L (5.0 micrograms/dL), achieving a specificity of 93%. There was no relation between acute glycemic control (as measured by the mean of 4 serum glucose values obtained before receiving dexamethasone) or chronic glycemic control (as measured by glycohemoglobin) and false positive responses to the 1 mg overnight DST. The mean of the measures of acute glycemic control of the 7 subjects who had false positive results, 14.4 +/- 2.8 mmol/L, was not significantly different than that of the 93 subjects with normal responses, 13.2 +/- 3.3 mmol/L. Similarly, the mean glycohemoglobin of the subjects with false positive results, 12.8 +/- 2.4%, was not significantly different than that of the subjects with normal responses, 12.9 +/- 2.5%. There was no correlation between plasma cortisol after dexamethasone and glycohemoglobin (r = 0.05), and only a weak correlation with the mean serum glucose (r = 0.21). We conclude that the 1 mg overnight DST is a valid screening test for Cushing's syndrome in patients with diabetes, regardless of glycemic control.

Autocrine regulation of endothelial exocytosis: von Willebrand factor release is induced by prostacyclin in cultured endothelial cells.

Vascular endothelial cells respond to external stimuli by altering the secretion of several bioactive molecules, including von Willebrand factor (vWf), prostacyclin (PGI2) and nitric oxide (NO). The release of all three molecules is regulated by a rise in cytosolic calcium ([Ca2+]i). In the present study we investigated whether cAMP-dependent signaling provides differential regulation of these effector systems by modulating the effect of [Ca2+]i in cultured human endothelial cells. The stable PGI2 analog iloprost, like other cAMP-raising agents (forskolin and adenosine), caused an acute dose-dependent increase in vWf release and potentiated the secretory response to thrombin. In contrast, iloprost, forskolin and adenosine failed to induce PGI2 release and inhibit thrombin-induced release. Our findings indicate cAMP-raising agents have opposite effects on [Ca2+]i-mediated vWf secretion and PGI2 release. PGI2 may potentiate vWf release and inhibit its own release in an autocrine manner.

Cellular mechanisms of the hemostatic effects of desmopressin (DDAVP).

The synthetic analog of vasopressin desmopressin (DDAVP) is widely used for the treatment of patients with von Willebrand disease (VWD), hemophilia A, several platelet disorders, and uremic bleeding. DDAVP induces an increase in plasma levels of von Willebrand factor (VWF), coagulation factor VIII (FVIII), and tissue plasminogen activator (t-PA). It also has a vasodilatory action. In spite of its extensive clinical use, its cellular mechanism of action remains incompletely understood. Its effect on VWF and t-PA as well as its vasodilatory effect are likely explained by a direct action on the endothelium, via activation of endothelial vasopressin V2R receptor and cAMP-mediated signaling. This leads to exocytosis from Weibel Palade bodies where both VWF and t-PA are stored, as well as to nitric oxide (NO) production via activation of endothelial NO synthase. The mechanism of action of DDAVP on FVIII plasma levels remains to be elucidated. The hemostatic effect of DDAVP likely involves additional cellular effects that remain to be discovered.

Desmopressin (DDAVP) induces NO production in human endothelial cells via V2 receptor- and cAMP-mediated signaling.

The hemostatic agent desmopressin (DDAVP) also has strong vasodilatory effects. DDAVP is a selective agonist for the vasopressin V2 receptor (V2R), which is coupled to cAMP-dependent signaling. DDAVP-induced vasodilation may be due to endothelial NO synthase (eNOS) activation. This hypothesis implies cAMP-mediated eNOS activation. It also implies wide extrarenal, endothelial V2R expression. We show that in human umbilical vein endothelial cells (HUVECs) the cAMP-raising agents forskolin and epinephrine increase NO production, as measured by a l-NMMA-inhibitable rise in cellular cGMP content. They also increase eNOS enzymatic activity, in a partly calcium-independent manner. cAMP-mediated eNOS activation is associated with phosphorylation of residue Ser1177, in a phosphatidyl inositol 3-kinase (PI3K)-independent manner. HUVECs do not express V2R. However, after heterologous V2R expression, DDAVP induces cAMP-dependent eNOS activation via Ser1177 phosphorylation. We have previously found V2R expression in cultured lung endothelial cells. By real time quantitative RT-PCR, we now find a wide V2R distribution notably in heart, lung and skeletal muscle. These results indicate that DDAVP and other cAMP-raising agents can activate eNOS via PI3K-independent Ser1177 phosphorylation in human endothelial cells. This mechanism most likely accounts for DDAVP-induced vasodilation.

Epinephrine induces von Willebrand factor release from cultured endothelial cells: involvement of cyclic AMP-dependent signalling in exocytosis.

von Willebrand factor (vWf) is released from endothelial cell storage granules after stimulation with thrombin, histamine and several other agents that induce an increase in cytosolic free calcium ([Ca2+]i). In vivo, epinephrine and the vasopressin analog DDAVP increase vWf plasma levels, although they are thought not to induce vWf release from endothelial cells in vitro. Since these agents act via a cAMP-dependent pathway in responsive cells, we examined the role of cAMP in vWf secretion from cultured human umbilical vein endothelial cells. vWf release increased by 50% in response to forskolin, which activates adenylate cyclase. The response to forskolin was much stronger when cAMP degradation was blocked with IBMX, an inhibitor of phosphodiesterases (+200%), whereas IBMX alone had no effect. vWf release could also be induced by the cAMP analogs dibutyryl-cAMP (+40%) and 8-bromo-cAMP (+25%); although their effect was weak, they clearly potentiated the response to thrombin. Epinephrine (together with IBMX) caused a small, dose-dependent increase in vWf release, maximal at 10(-6) M (+50%), and also potentiated the response to thrombin. This effect is mediated by adenylate cyclase-coupled beta-adrenergic receptors, since it is inhibited by propranolol and mimicked by isoproterenol. In contrast to thrombin, neither forskolin nor epinephrine caused an increase in [Ca2+]i as measured by fura-2 fluorescence. In addition, the effects of forskolin and thrombin were additive, suggesting that they act through distinct signaling pathways. We found a close correlation between cellular cAMP content and vWf release after stimulation with epinephrine and forskolin. These results demonstrate that cAMP-dependent signaling events are involved in the control of exocytosis from endothelial cells (an effect not mediated by an increase in [Ca2+]i) and provide an explanation for epinephrine-induced vWf release.

Acute von Willebrand factor secretion from the endothelium in vivo: assessment through plasma propeptide (vWf:AgII) Levels.

Elevated plasma concentrations of von Willebrand factor (vWf) are increasingly recognized as a cardiovascular risk factor, and are used as a marker of endothelial activation. However, the factors which determine the rate of vWf release from the endothelium in vivo have not been defined clearly. In addition, vWf plasma levels may also be influenced by adhesion of vWf to the vascular wall or to platelets, and by its rate of degradation. The propeptide of vWf (also called vWf:AgII) is stored and released in equimolar amounts with vWf. In the present study we attempted to determine whether this propeptide could be a more reliable marker of endothelial secretion than vWf itself. To accomplish this we developed an ELISA based on monoclonal antibodies. The propeptide levels in normal plasma were found to be 0.7 microgram/ml, more than 10 times lower than vWf itself. Administration of desmopressin (DDAVP) induced a rapid relative increase in propeptide (from 106 to 879%) and in vWf (from 112 to 272%). However, the increases in vWf and propeptide were equivalent when expressed in molar units. A time course study indicated a half-life of the propeptide of 3 h or less. In a baboon model of disseminated intravascular coagulation (DIC) induced by FXa, vWf increased by less than 100%, whereas the propeptide concentrations increased by up to 450%. In view of the massive thrombin generation (as assessed by fibrinogen depletion), the increases in vWf are small, compared to the strong secretory response to thrombin and fibrin previously observed in vitro. Our results suggest that due to its rapid turnover, the propeptide could provide a sensitive plasma marker of acute endothelial secretion.