Agonist-dependent traffic of raft-associated Ras and Raf-1 is required for activation of the mitogen-activated protein kinase cascade

Stimulation of HIRcB fibroblasts with insulin leads to accumulation of active components of the mitogen-activated protein kinase cascade in endocytic compartments. However, the factors that regulate the mobilization of these components through the endocytic pathway and the relevance of this event to cellular signaling remain unclear. Here we report that Ras proteins are associated with lipid rafts in resting HIRcB fibroblasts. Ras is rapidly internalized into the endocytic compartment following stimulation with insulin. The redistribution of Ras is independent of its activation. Attachment of the C-terminal 20 amino acids of Ha-Ras to green fluorescent protein was sufficient to target this construct to the same loci as the endogenous Ras protein, indicating that Ras distribution is a consequence of the association of its lipid modified C terminus with membranes. Depletion of plasma membrane cholesterol delocalized Ras and blocked insulin-dependent Ras traffic. Cholesterol depletion also blocked insulin-dependent phosphorylation of MEK and mitogen-activated protein kinase (MAPK) but had no effects on the translocation and activation of Raf-1. A second inhibitor of endocytosis, cytochalasin D, also blocked insulin-dependent MAPK phosphorylation. Taken together, these results suggest that mobilization of active Raf-1 through the endocytic compartment is required for completion of the MAPK cascade.

Decrease of adenylyl cyclase activity and expression by a sigma1 receptor ligand and putative atypical antipsychotic

We examined whether changes in the adenylyl cyclase system could be induced by the administration of the sigma1 receptor ligand and putative atypical antipsychotic 4-[4-fluorophenyl]-1,2,3,6-tetrahydro-1-[4-[1,-2,4-triazol-1-il]butyl]pyridine citrate) (E-5842). Repeated (21 days) but not acute (2 h) treatment with E-5842 induced a significant decrease in adenylyl cyclase type I immunoreactivity and adenylyl cyclase activity in rat frontal cortex membranes, with less or no effect in other brain regions such as the hippocampus or the striatum. Changes in immunoreactivity were not observed in other adenylyl cyclases (type V/VI). The reported changes, observed only after a chronic treatment, could be related to the mechanism of action of sigma receptor ligands in general or to that of E-5842 in particular and should be taken into account, given the long duration of treatment in psychiatric patients.

Brain-stem auditory evoked potentials in children with perinatal encephalopathies

OBJECTIVE

We sought to describe if neurological damage, in terms of brain lesions, syndrome and syndrome severity led to abnormalities in the brain-stem auditory evoked potentials (BAEPs) in order to provide a profile of children that could be used as an indicator of subsequent neurological sequelae. We analyzed the BAEPs from a group of children having prior evidence of neurological damage and determined the presence of neurological sequelae when the subjects were 3 years old.

METHODS

Brain-stem auditory evoked potentials (BAEPs) were carried out in a group of 154 children with perinatal neurological damage. The children were classified with neurofunctional (clinical and EEG alterations) or organic and neurofunctional brain disease (clinical, EEG and image alteration) and were all followed from the first month of life and serially for 3 years. We used principal component analysis (PCA), clustered analysis and linear correlation to determine association between BAEPs, risk factors and future sequelae.

RESULTS

Latencies of BAEPs decreased significantly with age, and the time of conduction was modified by the presence of neurological damage. All statistical analyses suggested positive and significant associations between risk factors (trophism and condition at birth), and the latencies of waves I, III and V as well as with IPL III-V (interpeak latency) and I-V. PCA showed that IPL I-III was also positively associated with condition at birth, severity of the neurological syndrome and encephalopathy. In addition, we found that the presence and type of sequela reflected changes in the latencies of the waves, as well as IPLs, primarily those of IPL I-III.

CONCLUSIONS

Our results suggest that statistical methods are often needed to analyze neurological damage. The relation between BAEPs, risk factors and neurological sequelae allowed us to obtain a profile of children, which can be then used as an aid in the prognosis of children having a risk of developing neurological sequelae.

Changes in phosphoinositide signalling activity and levels of the alpha subunit of G(q/11) protein in rat brain induced by E-5842, a sigma(1) receptor ligand and potential atypical antipsychotic

Changes in the phosphoinositide (PPI) signal transduction system induced by E-5842, a new sigma(1) (sigma(1)) receptor ligand and potential atypical antipsychotic, were studied in the rat frontal cortex, hippocampus and striatum. Acute treatment with E-5842 increased phospholipase C (PLC) activity in the striatum and the hippocampus. Chronic treatment with E-5842 induced an increase in the activity of PLC in the frontal cortex and the striatum. Similar up-regulation of the activity of the enzyme was also observed in rat frontal cortex membranes in presence of GTPgammaS. After chronic treatment with E-5842, it was also observed a significant increase of the immunoreactivity levels of G(q/11)alpha in the frontal cortex. Our results suggest that part of the antipsychotic effects of E-5842 could be related to the regulation of the PPI signal transduction pathway, especially after a prolonged treatment.

The recruitment of Raf-1 to membranes is mediated by direct interaction with phosphatidic acid and is independent of association with Ras

The serine/threonine kinase Raf-1 is an essential component of the MAPK cascade. Activation of Raf-1 by extracellular signals is initiated by association with intracellular membranes. Recruitment of Raf-1 to membranes has been reported to be mediated by direct association with Ras and by the phospholipase D product phosphatidic acid (PA). Here we report that insulin stimulation of HIRcB fibroblasts leads to accumulation of Ras, Raf-1, phosphorylated MEK, phosphorylated MAPK, and PA on endosomal membranes. Mutations that disrupt Raf-PA interactions prevented recruitment of Raf-1 to membranes, whereas disruption of Ras-Raf interactions did not affect agonist-dependent translocation. Expression of a dominant-negative Ras mutant did not prevent insulin-dependent Raf-1 translocation, but inhibited phosphorylation of MAPK. Finally, the PA-binding region of Raf-1 was sufficient to target green fluorescent protein to membranes, and its overexpression blocked recruitment of Raf-1 to membranes and disrupted insulin-dependent MAPK phosphorylation. These results indicate that agonist-dependent Raf-1 translocation is primarily mediated by a direct interaction with PA and is independent of association with Ras.

Patients with ascites have higher variceal pressure and wall tension than patients without ascites

OBJECTIVE

It has been suggested that ascites is a risk factor for variceal bleeding. Recently, it has been demonstrated that total paracentesis decreases variceal pressure. However, no data are available showing the basal variceal pressure in patients with and without ascites.

METHODS

We studied 76 cirrhotic patients, 49 with and 27 without ascites. Variceal pressure was measured by direct puncture. Variceal size, variceal pressure gradient, and variceal wall tension were also obtained.

RESULTS

No demographic differences were observed between the groups. Child score was higher (9.7+/-1.5 vs 7.8+/-2.1, p < 0.001) and serum albumin lower (2.6+/-0.6 vs 3.0+/-0.7 mg %, p < 0.02) in ascitic than in nonascitic patients, respectively. Variceal pressure and variceal pressure gradient were significantly higher in patients with ascites than in those without ascites (25.0+/-6 vs 20.4+/-4.6 mm Hg, p < 0.001 and 18.75+/-4.7 vs 13.70+/-4.1 mm Hg, p < 0.0001, respectively). The variceal wall tension was significantly higher in patients with ascites (71.0+/-25.1 mm Hg/mm) than in those without ascites (55.1+/-22.1 mm Hg/mm, p < 0.03). No relationship was observed between variceal pressure gradient and liver function. Ascites patients included in Child-Pugh grade A+B presented a similar variceal pressure to Child C patients (18.5+/-4.2 vs 19.3+/-5.7 mm Hg, respectively, p = ns). In addition, no relationship was observed between variceal pressure gradient and etiology of cirrhosis.

CONCLUSION

Our results demonstrate that patients with ascites have significantly higher variceal pressure and wall tension than patients without ascites. These results suggest that patients with ascites may be at risk for variceal bleeding.

The activation of phospholipase D by endothelin-1, angiotensin II, and platelet-derived growth factor in vascular smooth muscle A10 cells is mediated by small G proteins of the ADP-ribosylation factor family

We show here that A10 cells express the phospholipase D (PLD) isoforms PLD1b and PLD2. The activation of PLD in these cells by angiotensin II (AngII), endothelin-1 (ET-1), and platelet-derived growth factor (PDGF) was found to be sensitive to inhibitors of the activation of ADP-ribosylation factor (ARF) but not to blockers of Rho protein function. PDGF, AngII, and ET-1 induced the binding of ARF proteins to cell membranes in a permeabilized cell assay. Cells permeabilized and depleted of ARF were no longer sensitive to stimulation with AngII, ET-1, or PDGF, but the addition of recombinant myristoylated human ARF1 restored agonist-dependent PLD activity. Expression of dominant negative ARF mutants blocked receptor-dependent activation of PLD. PLD activity was also potently stimulated by treatment with phorbol esters, but this activity was only partially inhibited by brefeldin A or by the overexpression of ARF dominant negative mutants. Transient expression of catalytically inactive mutants of PLD2, but not PLD1, inhibited significantly PDGF- and AngII-dependent PLD activity. We conclude: 1) the activation of PLD by cell surface receptors occurs primarily by an ARF-dependent mechanism in A10 cells, whereas the activation of PLD by protein kinase C-dependent pathways is only partially dependent on the regulation of ARF proteins; and 2) cell surface receptors, such as AngII and PDGF, signal primarily via PLD2 in A10 cells.

Efficacy of octreotide and sclerotherapy in the treatment of acute variceal bleeding in cirrhotic patients. A prospective, multicentric, and randomized clinical trial

BACKGROUND

Sclerotherapy is the most widely used method for treatment of acute variceal bleeding. Previous reports have suggested that octreotide infusion is as effective as sclerotherapy. Our aim was to investigate the efficacy and safety of octreotide in comparison with sclerotherapy in controlling variceal bleeding.

METHODS

Seventy-six cirrhotic patients were randomized to receive either sclerotherapy (n = 37) or octreotide (n = 39) infusion of 50 microg/h intravenously for 48 h after a bolus of 100 microg, followed by subcutaneous injection of 100 microg/8 h for an additional 72 h.

RESULTS

The two groups were similar in base-line data. A similar initial control of bleeding was obtained in 94.6% for sclerotherapy and 84.6% for octreotide (NS). No difference was observed between sclerotherapy and octreotide in rebleeding (23% versus 33%) and treatment failure (22% versus 36%, respectively). Furthermore, the overall success of treatment was 78% for sclerotherapy and 64% for octreotide. No significant difference in mortality was observed between treatments (eight patients for octreotide and three patients for sclerotherapy, NS).

CONCLUSIONS

These results show that both treatments present a very high and similar initial and final control of bleeding. However, there is a trend that could be clinically important towards better results in the patients treated with sclerotherapy.

Up-regulation of sigma(1) receptor mRNA in rat brain by a putative atypical antipsychotic and sigma receptor ligand

Sigma(1) (sigma(1)) receptor mRNA expression was studied in the prefrontal cortex, striatum, hippocampus and cerebellum of rat brain by northern blot and in situ hybridization. The effects of a chronic treatment with antipsychotic drugs (haloperidol and clozapine), and with E-5842, a sigma(1) receptor ligand and putative atypical antipsychotic on sigma(1) receptor expression were examined. A significant increase in the levels of sigma(1) receptor mRNA in the prefrontal cortex and striatum after E-5842 administration was observed, while no apparent changes were seen with either haloperidol or clozapine. Our results suggest a long-term adaptation of the sigma(1) receptor at the level of mRNA expression in specific areas of the brain as a response to a sustained treatment with E-5842.

Terlipressin is more effective in decreasing variceal pressure than portal pressure in cirrhotic patients

BACKGROUND/AIMS

Terlipressin decreases portal pressure. However, its effects on variceal pressure have been poorly investigated. This study investigated the variceal, splanchnic and systemic hemodynamic effects of terlipressin.

METHODS

Twenty cirrhotic patients with esophageal varices grade II-III, and portal pressure > or =12 mmHg were studied. Hepatic venous pressure gradient, variceal pressure and systemic hemodynamic parameters were obtained. After baseline measurements, in a double-blind administration, 14 patients received a 2mg/iv injection of terlipressin and six patients received placebo. The same measurements were repeated 60 min later.

RESULTS

No demographic or biochemical differences were observed in basal condition between groups. Terlipressin produced significant decreases in intravariceal pressure from 20.9+4.9 to 16.3+/-4.7 mmHg (p<0.01, -21+/- 16%), variceal pressure gradient from 18.9+/-4.8 to 13.5+/-6.0 mmHg (p<0.01, -28+/-27%), estimated variceal wall tension from 78+/-29 to 59+/-31 mmHg x mm (p<0.01, -27+/-22%), and hepatic venous pressure gradient from 19.4+/-4.5 to 16.8+/-5 mmHg (p<0.01, -14+/-12%) at 60 min. The change in variceal pressure after 60 min of terlipressin administration was greater than the change in wedge hepatic venous pressure (-4.7 mmHg vs -0.5 mmHg, respectively, p<0.0001). Terlipressin also caused significant decreases in heart rate and cardiac index and increases in mean arterial pressure and peripheral vascular resistance.

CONCLUSIONS

Our results demonstrate that terlipressin produces significant and prolonged decreases in variceal pressure and variceal wall tension and has intrinsic effects on portal pressure and systemic hemodynamics. Variceal pressure provides a better assessment of the effects of terlipressin administration on esophageal varices than hepatic venous pressure gradient.

Variceal band ligation and variceal band ligation plus sclerotherapy in the prevention of recurrent variceal bleeding in cirrhotic patients: a randomized, prospective and controlled trial

BACKGROUND

The combination treatment of band ligation plus sclerotherapy has been proposed to hasten variceal eradication. The aim of this study was to assess the efficacy of band ligation alone versus band ligation plus sclerotherapy in the prevention of recurrent variceal bleeding.

METHODS

Eighty cirrhotic patients were randomized to group I (band ligation) with 41 patients or to group II (band ligation plus sclerotherapy) with 39 patients in whom polidocanol (2%) was injected 1 to 2 cm proximal to each band.

RESULTS

At baseline, both groups were similar with regard to clinical, demographic and laboratory data. Mean follow-up time (standard error) for group I was 336.5 +/- 43.4 days and for group II 386.1 +/- 40.1 days (p = 0.4). No statistical differences were observed between group I and group II in relation to recurrence of bleeding (31.7% vs. 23%, p = 0.38), treatment failure (24.4% vs. 12. 8%, p = 0.18), death (39% vs. 30.8%, p = 0.44) and variceal eradication (65.8% vs. 74.4%, p = 0.40). Group II had a significantly higher number of complications than group I, 30.8% versus 7.3%, respectively (p = 0.05). The number of bleeding related deaths was higher in group I than in group II (22% vs. 10.3%, respectively; p = 0.15).

CONCLUSIONS

No significant difference was observed between band ligation and band ligation plus sclerotherapy in prevention of recurrent variceal bleeding. Furthermore, there was a higher incidence of complications in the latter group.

Involvement of Shc and Cbl-PI 3-kinase in Lyn-dependent proliferative signaling pathways for G-CSF

Granulocyte colony-stimulating factor (G-CSF) is the major hematopoietic factor which controls the production and differentiation of granulocytes. The G-CSF receptor (G-CSFR) belongs to the superfamily of the cytokine receptors, which transduce signals via the activation of cytosolic protein tyrosine kinases (PTK). To determine the role of specific PTK in G-CSF signaling we expressed the human G-CSFR in cell lines derived from DT40 B cells, which lack either the Src-related Lyn or Syk. Wild-type (wt) and syk-deficient cells underwent increased DNA synthesis in response to G-CSF; lyn-deficient cells did not. The purpose of these studies is to identify Lyn's downstream effectors in mediating DNA synthesis. While G-CSF stimulated Ras activity in all cell lines, G-CSF failed to induce the tyrosine phosphorylation of Shc in lyn-deficient cells. G-CSF induced a statistically significant activation of Erk1/Erk2 Kinase or p90Rsk only in the wt cells. G-CSF induced the tyrosine phosphorylation of Cbl and increased activity of PI 3-kinase in wild-type and syk-deficient, but non in lyn-deficient, cells. Inhibition of Shc by over-expression of its SH2 or PTB domains or PI 3-kinase by either treatment with wortmannin or expression of the CblY731F mutant decreased G-CSF-induced DNA synthesis. Thus, the Lyn, Cbl-PI 3-kinase, and Shc/non-Ras-dependent pathways correlate with the ability of cells to respond to G-CSF with increased DNA synthesis.

The KDEL receptor regulates a GTPase-activating protein for ADP-ribosylation factor 1 by interacting with its non-catalytic domain

ADP-ribosylation factor 1 (ARF1) is a key regulator of transport in the secretory system. Like all small GTPases, deactivation of ARF1 requires a GTPase-activating protein (GAP) that promotes hydrolysis of GTP to GDP on ARF1. Structure-function analysis of a GAP for ARF1 revealed that its activity in vivo requires not only a domain that catalyzes hydrolysis of GTP on ARF1 but also a non-catalytic domain. In this study, we show that the non-catalytic domain of GAP is required for its recruitment from cytosol to membranes and that this domain mediates the interaction of GAP with the transmembrane KDEL receptor. Blocking its interaction with the KDEL receptor leaves the GAP cytosolic and prevents the deactivation in vivo of Golgi-localized ARF1. Thus, these findings suggest that the KDEL receptor plays a critical role in the function of GAP by regulating its recruitment from cytosol to membranes, where it can then act on its membrane-restricted target, the GTP-bound form of ARF1.

The role of G proteins in insulin signalling

Insulin modulates many intracellular processes including cellular metabolism, cell proliferation and cell differentiation. Some of these processes involve significant changes in the traffic of intracellular vesicles or in the structural organization of the cell. These phenomena have been linked to the activity of regulatory GTP-binding proteins. Most, if not all functions, of the insulin receptor are associated with its tyrosine kinase activity. Thus, over the past few years, a significant effort has been dedicated to elucidate the cross-talk between the tyrosine kinase activity of the receptor and the regulation of G protein-mediated pathways. Recent progress indicates that G proteins may mediate the control of several of insulin's intracellular functions. These include the regulation of the MAP kinase pathway, the activation of phospholipase D and the regulation of glucose uptake. This article discusses some recent advances in this area.

Pharmacological characteristics and regulation of 5-HT receptor-stimulated phosphoinositide hydrolysis in the rat spinal cord

In slices from immature rat spinal cord, both 5-hydroxytryptamine (5-HT) and the 5-HT2A/C receptor agonists (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and alpha-methyl-5-HT (alpha-Me-5-HT) stimulate phosphoinositide (PI) hydrolysis. PI breakdown is also increased by the 5-HT3 receptor agonist 2-Me-5-HT but not by phenylbiguanide. The effect of either 5-HT or DOI is blocked by selective 5-HT2A receptor antagonists such as spiperone and ketanserin and more markedly by mixed 5-HT2 receptor antagonists, such as ritanserin, methysergide and mesulergine, with higher affinity at the 2C subtype. The effect of 2-Me-5-HT is blocked by 5-HT2 and not by 5-HT3 receptor antagonists, indicating that 5-HT3 receptors do not directly or indirectly take part in PI hydrolysis in the spinal cord. Moreover, lesion with neonatal capsaicin of thin primary afferents to the dorsal spinal cord enhances inositol phosphate formation stimulated by 5-HT or DOI but not by 2-Me-5-HT. This lesion also increases 5-HT2A and 5-HT2C receptor density. After neonatal injection of 5,7-dihydroxytryptamine, which results in a marked loss of 5-HT content in the cord, 5-HT and 5-HT2 receptor agonists also enhance PI breakdown without a concomitant change in receptor number. The results suggest that the 5-HT-stimulated PI response in the rat spinal cord is associated only with the 5-HT2 receptor class, in particular with the 5-HT2C subtype.

[Familial hypercholesterolemia and plasma Lp(a) levels: 2 cardiovascular risk factors]

OBJECTIVE

Lipoprotein (a) (Lp(a)) is a modified LDL particle in human plasma. Elevated Lp(a) plasma concentration has been associated with increase risk of premature heart disease in most cross-sectional studies. Familial hypercholesterolemia (FH) is a genetic disorder characterized by an elevation of LDL cholesterol (LDL-C) caused by molecular defects in the LDL receptor gene. The aim of our study is to analyze Lp(a) values in a genetic diagnosed FH group without coronary heart disease (CHD) and explain the considerable variation in clinical severity of FH patients.

METHOD

We have study plasma lipids and lipoprotein levels in 60 subjects with familial hypercholesterolemia without CHD and in 74 normolipidemic controls without personal history of CHD and dyslipidemia of the Valencia area in Spain.

RESULTS

We found differences in total and LDL cholesterol levels and apo B values as expected and also in plasma Lp(a) levels and log transformed values between FH subjects and normolipidemic controls (22.3 mg/dl +/- 19.4 vs 12.5 mg/dl +/- 12.6 p = 0.001 and 1.12 +/- 0.53 vs. 0.84 +/- 0.58 p = 0.008). The percentage of FH subjects with a cut point Lp(a) value > 20 mg/dl is significantly elevated in this group (47% vs 21% p = 0.002). Because of family relationships within the entire study population we also have compared 23 FH probands with the normolipidemic controls. Again the same results have been obtained (Lp(a) levels of 23.21 mg/dl +/- 19.2 vs 12.54 mg/dl +/- 12.63 p = 0.019 and log Lp(a) values of 1.19 +/- 0.42 vs 0.84 +/- 0.58 p = 0.01).

CONCLUSION

Our results indicate that FH subjects will have a more cardiovascular risk due to the potentiation of hypercholesterolemia and elevated Lp(a) values, indicating the addition effects of two different locus implicated in premature coronary heart disease and could explain the considerable variation in clinical severity of FH.

Phospholipase D and its product, phosphatidic acid, mediate agonist-dependent raf-1 translocation to the plasma membrane and the activation of the mitogen-activated protein kinase pathway

The primary known function of phospholipase D (PLD) is to generate phosphatidic acid (PA) via the hydrolysis of phosphatidylcholine. However, the functional role of PA is not well understood. We report here evidence that links the activation of PLD by insulin and the subsequent generation of PA to the activation of the Raf-1-mitogen-activated protein kinase (MAPK) cascade. Brefeldin A (BFA), an inhibitor of the activation of ADP-ribosylation factor proteins, inhibited insulin-dependent production of PA and MAPK phosphorylation. The addition of PA reversed the inhibition of MAPK activation by BFA. Overexpression of a catalytically inactive variant of PLD2, but not PLD1, blocked insulin-dependent activation of PLD and phosphorylation of MAPK. Real time imaging analysis showed that insulin induced Raf-1 translocation to cell membranes by a process that was inhibited by BFA. PA addition reversed the effects of BFA on Raf-1 translocation. However, PA did not activate Raf-1 in vitro or in vivo, suggesting that the primary function of PA is to enhance the recruitment of Raf-1 to the plasma membrane where other factors may activate it. Finally, we found that the recruitment of Raf-1 to the plasma membrane was transient, but Raf-1 remained bound to endocytic vesicles.

Metabolic modulation of acute myocardial infarction. The ECLA (Estudios Cardiológicos Latinoamérica) Collaborative Group

BACKGROUND

Several trials have been performed in the past using glucose, insulin, and potassium infusion (GIK) for the treatment of acute myocardial infarction (AMI). Because of continuing uncertainty about the potential role of this therapeutic intervention, we conducted a randomized trial to evaluate the impact of a GIK solution during the first hours of AMI.

METHODS AND RESULTS

Four hundred seven patients with suspected AMI admitted within 24 hours of symptoms onset were enrolled. In a ratio of 2:1, 268 patients were allocated to receive GIK (high- or low-dose) and 139 to receive control. Phlebitis and serum changes in the plasma concentration of glucose or potassium were observed more often with GIK. A trend toward a nonsignificant reduction in major and minor in-hospital events was observed in patients allocated to GIK. In 252 patients (61.9%) treated with reperfusion strategies, a statistically significant reduction in mortality (relative risk [RR] 0.34; 95% CI: 0.15 to 0.78; 2P=0.008) and a consistent trend toward fewer in-hospital events in the GIK group were observed.

CONCLUSIONS

Our results confirm that a metabolic modulation strategy in the first hours of an AMI is feasible, applicable worldwide, and has mild side effects. The statistically significant mortality reduction in patients who underwent a reperfusion strategy might have important implications for the management of AMI patients. It is now essential to perform a large-scale trial to reliably determine the magnitude of benefit.

ADP-ribosylation factor proteins mediate agonist-induced activation of phospholipase D

The role of small G proteins of the ADP-ribosylation factor (ARF) and Rho families on the activation of phospholipase D (PLD) by platelet-derived growth factor (PDGF) and phorbol esters (PMA) has been investigated. The activation of PLD by PDGF and PMA was blocked by brefeldin A (BFA), an inhibitor of ARF activation, but not by Clostridium botulinum C3 exotoxin, an inhibitor of the activity of Rho. PDGF and PMA, in the presence of GTPgammaS, promoted the association of ARF and RhoA with cell membranes. Cells depleted of ARF and Rho by digitonin permeabilization showed a significant reduction of the activity of phospholipase D. Recombinant ARF was sufficient to restore agonist-induced PLD activity to digitonin-permeabilized, cytoplasm-depleted cells. In contrast, isoprenylated recombinant RhoA had no effects in this reconstitution assay. HIRcB cells were transiently transfected with wild-type and dominant-negative mutants of ARF1 and ARF6. Neither wt-ARF1 nor wt-ARF6 had any effects on agonist-dependent PLD activity. However, dominant-negative ARF1 and ARF6 mutants blocked the stimulation of PLD by PDGF but only partially inhibited the effects of PMA. These results demonstrate that ARF rather than Rho proteins mediate the activation of PLD by PDGF and phorbol esters in HIRcB fibroblasts.

The quality of private and public primary health care management of children with diarrhoea and acute respiratory infections in Tlaxcala, Mexico

In Tlaxcala, Mexico, 80% of the children who died from diarrhoea or acute respiratory infections (ARI) in 1992-1993 received medical care; in more than 70% of cases it was provided by a private general practitioner (GP). The present study evaluated the quality of case management by private and public GPs to children under five years of age with diarrhoea and ARI. During the clinical observation, the treatment and counselling given to the mother were assessed with the WHO guidelines as reference standard. A total of 41 private and 40 public GPs were evaluated for the management of diarrhoea, and 59 private and 40 public GPs for the management of ARI. For diarrhoea, half of the private GPs gave inadequate rehydration therapy, 63% gave incorrect advice on diet, 66% and 49% made an incorrect correct decision in the prescription of antimicrobial and symptomatic drugs, respectively. Public GPs generally performed better in diarrhoea management: 7% gave inadequate rehydration therapy, 13% gave wrong advice on diet, 3% made a wrong decision in the prescription of symptomatic drugs and 28% gave a wrong decision in antimicrobial prescription. In the management of ARI, 66% and 58% of private GPs made a wrong decision in the prescription of antimicrobial and symptomatic drugs, respectively, compared to 30% and 20% of public GPs, respectively. Counselling to the mother given by both private and public GPs was considered inadequate in most cases of diarrhoea and ARI. These results clearly show that private doctors, as important providers of medical care, need to be included in the strategies to improve the quality of care of children with diarrhoea and ARI. Future research needs to address the determinants of the clinical practice of private doctors in countries like Mexico.