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Biomedical subjects

P Nicod

Publications and source records attributed to P Nicod.

At least 55 records · Page 3Linked to original sources
PubMed1998

IB1, a JIP-1-related nuclear protein present in insulin-secreting cells.

JIP-1 is a cytoplasmic inhibitor of the c-Jun amino-terminal kinase activated pathway recently cloned from a mouse brain cDNA library. We report herein the expression cloning of a rat cDNA encoding a JIP-1-related nuclear protein from a pancreatic beta-cell cDNA library that we named IB1 for Islet-Brain 1. IB1 was isolated by its ability to bind to GTII, a cis-regulatory element of the GLUT2 promoter. The IB1 cDNA encodes a 714-amino acid protein, which differs from JIP-1 by the insertion of 47 amino acids in the carboxyl-terminal part of the protein. The remaining 667 amino acids are 97% identical to JIP-1. The 47-amino acid insertion contains a truncated phosphotyrosine interaction domain and a putative helix-loop-helix motif. Recombinant IB1 (amino acids 1-714 and 280-714) was shown to bind in vitro to GTII. Functionally IB1 transactivated the GLUT2 gene. IB1 was localized within the cytoplasm and the nucleus of insulin-secreting cells or COS-7 cells transfected with an expression vector encoding IB1. Using a heterologous GAL4 system, we localized an activation domain of IB1 within the first 280 amino acids of the protein. These data demonstrate that IB1 is a DNA-binding protein related to JIP-1, which is highly expressed in pancreatic beta-cells where it functions as a transactivator of the GLUT2 gene.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Haemodynamic and sympathetic effects of inhibition of nitric oxide synthase by systemic infusion of N(G)-monomethyl-L-arginine into humans are dose dependent.

BACKGROUND: In several animal species, nitric oxide (NO) buffers central neural sympathetic outflow, but data concerning humans are sparse and conflicting. We hypothesized that these conflicting results could be related to large differences in the dose of N(G)-monomethyl-L-arginine, a stereospecific inhibitor of NO synthase, infused in these human studies. OBJECTIVE: To investigate the haemodynamic and sympathetic effects of systemic inhibition of NO synthase by intravenous infusion of two different doses of N(G)-monomethyl-L-arginine into healthy humans and compare these effects with those of an equipressor dose of the non-endothelium-dependent vasoconstrictor phenylephrine. METHODS: Muscle sympathetic nerve activity was measured by microneurography and blood flow by venous occlusion plethysmography. N(G)-monomethyl-L-arginine was infused over 15 min at a rate of 50 microg/kg per min into members of one group (n = 8) and at a rate of 450 microg/kg per min into members of another group (n = 7). An equipressor dose of phenylephrine was infused into four subjects from each group. RESULTS: Infusions of N(G)-monomethyl-L-arginine and of phenylephrine at the higher dose similarly suppressed sympathetic activity. In contrast, infusions of N(G)-monomethyl-L-arginine and of an equipressor dose of phenylephrine at the lower dose had different sympathetic effects. Burst frequency of muscle sympathetic nerve activity remained unchanged during infusion of N(G)-monomethyl-L-arginine but decreased by roughly 50% during infusion of phenylephrine. Infusion of N(G)-monomethyl-L-arginine at both doses did not alter forearm blood flow. Only infusion of N(G)-monomethyl-L-arginine at the higher dose increased forearm vascular resistance. CONCLUSIONS: Haemodynamic and sympathetic effects of inhibition of NO synthase by infusion of N(G)-monomethyl-L-arginine into humans are dose dependent. At higher doses, N(G)-monomethyl-L-arginine exerts sympathoinhibitory effects that are comparable to those evoked by a non-specific vasoconstrictor drug, whereas at lower doses, it exerts sympatho-excitatory effects.

Adult↗
PubMed1998

Transcriptional activation of the macrophage migration-inhibitory factor gene by the corticotropin-releasing factor is mediated by the cyclic adenosine 3',5'- monophosphate responsive element-binding protein CREB in pituitary cells.

Macrophage migration-inhibitory factor (MIF) has recently been identified as a pituitary hormone that functions as a counterregulatory modulator of glucocorticoid action within the immune system. In the anterior pituitary gland, MIF is expressed in TSH- and ACTH-producing cells, and its secretion is induced by CRF. To investigate MIF function and regulation within pituitary cells, we initiated the characterization of the MIF 5'-regulatory region of the gene. The -1033 to +63 bp of the murine MIF promoter was cloned 5' to a luciferase reporter gene and transiently transfected into freshly isolated rat anterior pituitary cells. This construct drove high basal transcriptional activity that was further enhanced after stimulation with CRF or with an activator of adenylate cyclase. These transcriptional effects were associated with a concomitant rise in ACTH secretion in the transfected cells and by an increase in MIF gene expression as assessed by Northern blot analysis. A cAMP-responsive element (CRE) was identified within the MIF promoter region which, once mutated, abolished the cAMP responsiveness of the gene. Using this newly identified CRE, DNA-binding activity was detected by gel retardation assay in nuclear extracts prepared from isolated anterior pituitary cells and AtT-20 corticotrope tumor cells. Supershift experiments using antibodies against the CRE-binding protein CREB, together with competition assays and the use of recombinant CREB, allowed the detection of CREB-binding activity with the identified MIF CRE. These data demonstrate that CREB is the mediator of the CRF-induced MIF gene transcription in pituitary cells through an identified CRE in the proximal region of the MIF promoter.

Animals↗
PubMed1997

Cardiovascular and sympathetic effects of nitric oxide inhibition at rest and during static exercise in humans.

BACKGROUND: Nitric oxide (NO) regulates vascular tone and blood pressure, and studies in animals suggest that it does so, at least in part, by modulating sympathetic neural outflow. Loss of NO-induced vasodilator tone and restraint on sympathetic vasoconstrictor outflow could lead to exaggerated vasoconstrictor and pressor responses to physical stress in humans. METHODS AND RESULTS: To determine the role of NO in the modulation of central sympathetic outflow and vascular tone at rest and during a physical stress, we tested effects of systemic inhibition of NO synthase by N(G)-monomethyl-L-arginine (L-NMMA) infusion (a stereospecific inhibitor of NO synthase) on sympathetic nerve activity (microneurography), regional vascular resistance, and blood pressure at rest and during static handgrip. The major new findings are that (1) under resting conditions, L-NMMA infusion, which increased mean arterial pressure by approximately 10%, did not have any detectable effect on muscle sympathetic nerve activity, whereas a similar increase in arterial pressure evoked by phenylephrine infusion (an NO-independent vasoconstrictor) decreased the rate of sympathetic nerve firing by approximately 50%; (2) during static handgrip, the exercise-induced sympathetic nerve responses were preserved during L-NMMA infusion but markedly attenuated during phenylephrine infusion; and (3) the L-NMMA-induced loss of vasodilator tone did not result in exaggerated exercise-induced pressor and calf vasoconstrictor responses. CONCLUSIONS: These findings indicate that NO is involved in the central regulation of sympathetic outflow in humans and suggest that both neuronal and endothelial NO synthesis may contribute to the regulation of vasomotor tone.

Adrenergic alpha-Agonists↗
PubMed1997

The loss of GLUT2 expression in the pancreatic beta-cells of diabetic db/db mice is associated with an impaired DNA-binding activity of islet-specific trans-acting factors.

GLUT2 expression is reduced in the pancreatic beta-cells of several diabetic animals. The transcriptional control of the gene in beta-cells involves at least two islet-specific DNA-binding proteins, GTIIa and PDX-1, which also transactivates the insulin, somatostatin and glucokinase genes. In this report, we assessed the DNA-binding activities of GTIIa and PDX-1 to their respective cis-elements of the GLUT2 promoter using nuclear extracts prepared from pancreatic islets of 12 week old db/db diabetic mice. We show that the decreased GLUT2 mRNA expression correlates with a decrease of the GTIIa DNA-binding activity, whereas the PDX-1 binding activity is increased. In these diabetic animals, insulin mRNA expression remains normal. The adjunction of dexamethasone to isolated pancreatic islets, a treatment previously shown to decrease PDX-1 expression in the insulin-secreting HIT-T15 cells, has no effect on the GTIIa and PDX-1 DNA-binding activities. These data suggest that the decreased activity of GTIIa, in contrast to PDX-1, may be a major initial step in the development of the beta-cell dysfunction in this model of diabetes.

Animals↗
PubMed1997

[Voluntary mercury poisoning: biological consequences and psychiatric significance].

A young patient suffering from schizophrenia had intense headaches and photophobia which were induced by intra-ocular injections of mercury. The clinical diagnosis was established once foreign bodies were visualized on regular X-rays of the patients skull. The mercury intoxication in combination with the secondary irreversible lesions to the eyes necessitated a bilateral enucleation and the use of a chelating treatment with sodium-dimercapto-1-propane sulfate (DMP). Automutilation is a very rare and dramatic complication of schizophrenia. The psychiatric handling and meaning of such dramatic automutilation is discussed in this case report together with a recent review of the toxicologic treatment of mercury intoxication in humans.

Adult↗
PubMed1997

Insulin secretion is regulated by the glucose-dependent production of islet beta cell macrophage migration inhibitory factor.

Macrophage migration inhibitory factor (MIF), originally identified as a cytokine secreted by T lymphocytes, was found recently to be both a pituitary hormone and a mediator released by immune cells in response to glucocorticoid stimulation. We report here that the insulin-secreting beta cell of the islets of Langerhans expresses MIF and that its production is regulated by glucose in a time- and concentration-dependent manner. MIF and insulin colocalize by immunocytochemistry within the secretory granules of the pancreatic islet beta cells, and once released, MIF appears to regulate insulin release in an autocrine fashion. In perifusion studies performed with isolated rat islets, immunoneutralization of MIF reduced the first and second phase of the glucose-induced insulin secretion response by 39% and 31%, respectively. Conversely, exogenously added recombinant MIF was found to potentiate insulin release. Constitutive expression of MIF antisense RNA in the insulin-secreting INS-1 cell line inhibited MIF protein synthesis and decreased significantly glucose-induced insulin release. MIF is therefore a glucose-dependent, islet cell product that regulates insulin secretion in a positive manner and may play an important role in carbohydrate metabolism.

Animals↗
PubMed1997

Hypertension increases connexin43 in a tissue-specific manner.

BACKGROUND: Connexin43 (Cx43), a membrane protein involved in the control of cell-to-cell communication, is thought to play a role in the contractility of the vascular wall and in the electrical coupling of cardiac myocytes. The aim of this study was to investigate the effects of experimental hypertension on Cx43 expression in rat aorta and heart. METHODS AND RESULTS: Rats were made hypertensive after one renal artery was clipped (two kidney, one-clip renal model) or after the administration of deoxycorticosterone and salt (DOCA-salt model). After 4 weeks, all rats showed a similar increase in intra-arterial mean blood pressure and in the thickness of both the aortic wall and the heart. Northern blot analysis of aorta mRNA and immunolabeling for Cx43 showed that hypertensive rats expressed twice as much Cx43 in aorta as the control animals. In contrast, no difference in Cx43 mRNA or in the immunolabeled protein was observed in heart. CONCLUSIONS: The results show that rats exhibiting a similar degree of blood pressure elevation, as the result of different mechanisms, feature a comparable increase in Cx43 gene expression, which was observed in the aortic but not in the cardiac muscle. These data suggest that localized mechanical forces induced by hypertension are major tissue-specific regulators of Cx43 expression.

Animals↗
PubMed1997

[Epidemiology of cardiovascular diseases: role of ovarian hormones].

Cardiovascular diseases represent the major cause of mortality in industrialized countries, including Switzerland, and affect a large percentage of hospitalized patients and patients seen in outpatient clinics. Recently, a decline in the incidence of cardiovascular diseases has been observed, associated with a general improvement in prognosis. This has been attributed to progress achieved in the treatment of many cardiovascular diseases, and to a better identification and treatment of various risk factors. Differences in the clinical manifestations of cardiovascular diseases have been observed between men and women. Women seem to be protected until the time of menopause. In this review, various epidemiological aspects of cardiovascular diseases in men and women are discussed.

Adult↗
PubMed1997

Hypertension differentially affects the expression of the gap junction protein connexin43 in cardiac myocytes and aortic smooth muscle cells.

Electrical and mechanical coupling of myocytes in heart and of smooth muscle cells in the aortic wall is thought to be mediated by intercellular channels aggregated at gap junctions. Connexin43 (Cx43) is one of the predominant membrane proteins forming junctional channels in the cardiovascular system. This study was undertaken to assess its expression during experimental hypertension. Rats were made hypertensive by clipping one renal artery (two-kidney, one-clip renal hypertension) or by administering deoxycorticosterone and salt (DOCA-salt hypertension). After four weeks, rats from both models showed a similar increase in intra-arterial mean blood pressure, as well as in the thickness of both aorta and heart walls. Northern blot analysis showed that, compared to controls, hypertensive rats expressed twice more Cx43 in aorta, but not in heart. These results suggest that localized mechanical forces induced by hypertension are major tissue-specific regulators of Cx43 expression.

Animals↗
PubMed1997

In vivo and in vitro effects of somatostatin and insulin on glucagon release in a human glucagonoma.

Inhibition of pancreatic glucagon secretion has been reported to be mediated by glucose, insulin and somatostatin. As no human pancreatic alpha-cell lines are available to study in vitro the relative importance of insulin and glucose in the control of pancreatic glucagon release, we investigated a patient presenting with a malignant glucagonoma who underwent surgical resection of the tumour. Functional somatostatin receptors were present as octreotide administration decreased basal glucagon and insulin secretion by 52 and 74%, respectively. The removed tumour was immunohistochemically positive for glucagon, chromogranin A and pancreatic polypeptide but negative for insulin, gastrin and somatostatin. The glucagonoma cells were also isolated and cultured in vitro. Incubation experiments revealed that change from high (10 mM) to low (1 mM) glucose concentration was unable to stimulate glucagon secretion. A dose-dependent inhibition of glucagon release by insulin was however, observed at low glucose concentration. These findings demonstrate that insulin could inhibit glucagon secretion in vitro in the absence of elevated glucose concentrations. These data suggest, as observed in vivo and in vitro in several animal studies, that glucopenia-induced glucagon secretion in humans is not mediated by a direct effect of low glucose on alpha-cells but possibly by a reduction of insulin-mediated alpha-cell suppression and/or an indirect neuronal stimulation of glucagon release.

Chromogranin A↗
PubMed1997

Insulinoma associated with a case of multiple endocrine neoplasia type I: Functional somatostatin receptors and abnormal glucose-induced insulin secretion.

A sporadic case of multiple endocrine neoplasia type I with coexisting insulinoma and hyperparathyroidism was investigated in vivo and in vitro. The insulinoma was localized by somatostatin receptor scintigraphy and these receptors were functionally active. Octreotide administration decreased the basal insulin and glucagon secretion by 90 and 46%, respectively. Immunocytochemistry of the insulinoma tissue was positive for insulin, chromogranin A and neuropeptide Y. The insulinoma cells were also isolated and cultured in vitro. Incubation experiments revealed that a low glucose concentration (1 mmol/l) was sufficient to increase cytosolic free calcium and to produce a maximal glucose-induced insulin release. Northern blot analysis of RNA obtained from the tumor showed a high abundance of the low Km glucose transporter GLUT1 but no transcript for the high Km glucose transporter GLUT2. The abnormal distribution of glucose transporters probably relates to the abnormal glucose sensing of insulinoma cells, and explains their sustained insulin secretion at low glucose concentrations. Whether these abnormalities share a pathogenetic link with the presence of functionally active somatostatin receptors remains to be elucidated.

Actins↗
PubMed1996

[Rapidly progressive ascites].

A 50-year-old woman rapidly developed ascites with jaundice and worsening of general condition. On admission a nodule of the left breast was noted. Workup showed slight anomalies in liver tests and led to the diagnosis of portal hypertension, without visible lesion (CT scan, ultrasonography) of the liver. The patient suffered severe bleeding caused by esophageal varices necessitating urgent sclerotherapy. Several days later, her condition worsened rapidly due to acute respiratory distress syndrome followed by irreversible shock.

Ascites↗
PubMed1996

Inhaled nitric oxide for high-altitude pulmonary edema.

BACKGROUND: Pulmonary hypertension is a hallmark of high-altitude pulmonary edema and may contribute to its pathogenesis. When administered by inhalation, nitric oxide, an endothelium-derived relaxing factor, attenuates the pulmonary vasoconstriction produced by short-term hypoxia. METHODS: We studied the effects of inhaled nitric oxide on pulmonary-artery pressure and arterial oxygenation in 18 mountaineers prone to high-altitude pulmonary edema and 18 mountaineers resistant to this condition in a high altitude laboratory (altitude, 4559 m). We also obtained lung-perfusion scans before and during nitric oxide inhalation to gain further insight into the mechanism of action of nitric oxide. RESULTS: In the high-altitude laboratory, subjects prone to high-altitude pulmonary edema had more pronounced pulmonary hypertension and hypoxemia than subjects resistant to high-altitude pulmonary edema. Arterial oxygen saturation was inversely related to the severity of pulmonary hypertension (r=-0.50, P=0.002). In subjects prone to high-altitude pulmonary edema, the inhalation of nitric oxide (40 ppm for 15 minutes) produced a decrease in mean (+/-SD) systolic pulmonary-artery pressure that was three times larger than the decrease in subjects resistant to such edema (25.9+/-8.9 vs. 8.7+/-4.8 mm Hg, P<0.001). Inhaled nitric oxide improved arterial oxygenation in the 10 subjects who had radiographic evidence of pulmonary edema (arterial oxygen saturation increased from 67+/-10 to 73+/-12 percent, P=0.047), whereas it worsened oxygenation in subjects resistant to high-altitude pulmonary edema. The nitric oxide-induced improvement in arterial oxygenation in subjects with high-altitude pulmonary edema was accompanied by a shift in blood flow in the lung away from edematous segments and toward nonedematous segments. CONCLUSIONS: The inhalation of nitric oxide improves arterial oxygenation in high-altitude pulmonary edema, and this beneficial effect may be related to its favorable action on the distribution of blood flow in the lungs. A defect in nitric nitric oxide synthesis may contribute to high-altitude pulmonary edema.

Administration, Inhalation↗
PubMed1996

Neuropeptide Y secretion from a human insulinoma.

Neuropeptide Y (NPY) is a 36 aminoacid peptide known to inhibit glucose-stimulated insulin secretion. NPY has been shown to be synthesized and secreted by rat islets of Langerhans. More recently, we described the presence on NPY within human islets of Langerhans and in several pancreatic endocrine tumors. In this report, we describe the case of a patient presenting with an insulinoma who underwent the surgical resection of the tumor and was studied in vivo and in vitro for NPY production. Using a highly specific and sensitive two-site amplified enzyme-linked immunosorbent assay, we detected high plasma NPY levels in the patient prior to the surgical resection of the tumor which returned to normal after surgery. NPY was secreted from the tumor when kept in primary cell culture. Furthermore, immunohistochemistry of the insulinoma revealed the presence of NPY and its C-flanking peptide together with insulin, chromogranin and neuron specific enolase. It is concluded that elevated circulating NPY levels observed in this patient with an insulinoma reflected in vivo secretion by the tumor and it is hypothesized that NPY could potentially be used as an endocrine marker in patients with suspected insulinoma.

Aged↗
PubMed1996

Transcriptional activation of the GLUT2 gene by the IPF-1/STF-1/IDX-1 homeobox factor.

The homeodomain protein PDX-1, referred as IPF-1/STF-1/IDX-1, is a transcriptional factor that plays a critical role in the control of several genes expressed in the pancreatic islet. PDX-1 gene expression has been previously shown to be reduced in cultured beta-cell lines chronically exposed to high glucose concentrations. As the glucose transporter type 2 (GLUT2) gene expression is selectively decreased in the beta-pancreatic cells of experimental models of diabetes, we postulated that the loss of GLUT2 gene expression in the pancreatic islets of diabetic animals may be due to the loss of PDX-1 transacting function on the GLUT2 gene. We, therefore, investigated the potential role of PDX-1 in the transcriptional control of GLUT2. We have identified a repeat of a TAAT motif (5'-TAATA-ATAACA-3') conserved in the sequence of the human and murine GLUT2 promoters. Recombinant PDX-1 binds to this GLUT2TAAT motif in electrophoretic mobility shift experiments. PDX-1 antiserum detects the formation of the complex of PDX-1 with the GLUT2TAAT motif in nuclear extracts from the pancreatic insulin-secreting cell line, beta TC3. The GLUT2TAAT motif was mutated in the murine GLUT2 promoter (-1308/+49 bp) linked to a luciferase reporter gene and transfected into beta TC3 cells. Compared with the transcriptional activity of the wild type promoter, that of the mutated promoter decreases by 41%. Multiple copies of the GLUT2TAAT motif were ligated 5' to a heterologous promoter and transfected into a PDX-1-expressing cell line (beta TC3) and into cell lines lacking the homeobox factor (InR1-G9 and JEG-3). The GLUT2TAAT motif mediates the activation of the heterologous promoter in the PDX-1-expressing cell line but not in InR1-G9 or JEG-3 cell lines. Furthermore, cotransfection in a PDX-1-deficient cell line with the expression vector encoding PDX-1 transactivates specifically the heterologous promoter containing the multimerized GLUT2TAAT motif. These data demonstrate that the murine GLUT2 promoter is controlled by the PDX-1 homeobox factor through the identified GLUT2TAAT motif.

Animals↗
PubMed1995

A 338-bp proximal fragment of the glucose transporter type 2 (GLUT2) promoter drives reporter gene expression in the pancreatic islets of transgenic mice.

The high Km glucose transporter GLUT2 is a membrane protein expressed in tissues involved in maintaining glucose homeostasis, and in cells where glucose-sensing is necessary. In many experimental models of diabetes, GLUT2 gene expression is decreased in pancreatic beta-cells, which could lead to a loss of glucose-induced insulin secretion. In order to identify factors involved in pancreatic beta-cell specific expression of GLUT2, we have recently cloned the murine GLUT2 promoter and identified cis-elements within the 338-bp of the proximal promoter capable of binding islet-specific trans-acting factors. Furthermore, in transient transfection studies, this 338-bp fragment could efficiently drive the expression of the chloramphenicol acetyl transferase (CAT) gene in cell lines derived from the endocrine pancreas, but displayed no promoter activity in non-pancreatic cells. In this report, we tested the cell-specific expression of a CAT reporter gene driven by a short (338 bp) and a larger (1311 bp) fragment of the GLUT2 promoter in transgenic mice. We generated ten transgenic lines that integrated one of the constructs. CAT mRNA expression in transgenic tissues was assessed using the RNAse protection assay and the quantitative reverse transcribed polymerase chain reaction (RT-PCR). Overall CAT mRNA expression for both constructs was low compared to endogenous GLUT2 mRNA levels but the reporter transcript could be detected in all animals in the pancreatic islets and the liver, and in a few transgenic lines in the kidney and the small intestine. The CAT protein was also present in Langerhans islets and in the liver for both constructs by immunocytochemistry. These findings suggest that the proximal 338 bp of the murine GLUT2 promoter contain cis-elements required for the islet-specific expression of GLUT2.

Animals↗