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G Ribes

Publications and source records attributed to G Ribes.

At least 19 recordsLinked to original sources
PubMed2001

A constitutive nitric oxide synthase modulates insulin secretion in the INS-1 cell line.

We provide immunocytochemical evidence that the neuronal isoform of constitutive NO synthase (cNOS) is expressed in the rat insulinoma cell line INS-1. Furthermore, using N omega-nitro-L-arginine methyl ester (L-NAME), a pharmacological inhibitor of cNOS activity, we show that this enzyme is implicated in the modulation of insulin secretion in INS-1 cells. Indeed, in the presence of 2.8 mM glucose, L-NAME induced a specific and dose-dependent increase in insulin release, suggesting that cNOS exerts an inhibitory tone on basal insulin secretion. Moreover, L-arginine, the physiological substrate of cNOS, significantly reduced the marked enhancing effect of L-NAME on insulin release and to a lesser extent, at low concentrations, that of 10 mM KCl. L-NAME also potentiated the insulin secretion stimulated by 5.5 and 8.3 mM glucose, but in this case, its effect was not reduced by L-arginine. In conclusion, our data show that the neuronal isoform of cNOS exerts a negative modulation on insulin secretion in INS-1 cells, confirming the previous results obtained in the isolated perfused rat pancreas or pancreatic islets.

Animals↗
PubMed2001

A neuronal isoform of nitric oxide synthase expressed in pancreatic beta-cells controls insulin secretion.

Evidence is presented showing that a neuronal isoform of nitric oxide synthase (NOS) is expressed in rat pancreatic islets and INS-1 cells. Sequencing of the coding region indicated a 99.8% homology with rat neuronal NOS (nNOS) with four mutations, three of them resulting in modifications of the amino acid sequence. Double-immunofluorescence studies demonstrated the presence of nNOS in insulin-secreting beta-cells. Electron microscopy studies showed that nNOS was mainly localized in insulin secretory granules and to a lesser extent in the mitochondria and the nucleus. We also studied the mechanism involved in the dysfunction of the beta-cell response to arginine and glucose after nNOS blockade with N(G)-nitro-L-arginine methyl ester. Our data show that miconazole, an inhibitor of nNOS cytochrome c reductase activity, either alone for the experiments with arginine or combined with sodium nitroprusside for glucose, is able to restore normal secretory patterns in response to the two secretagogues. Furthermore, these results were corroborated by the demonstration of a direct enzyme-substrate interaction between nNOS and cytochrome c, which is strongly reinforced in the presence of the NOS inhibitor. Thus, we provide immunochemical and pharmacological evidence that beta-cell nNOS exerts, like brain nNOS, two catalytic activities: a nitric oxide production and an NOS nonoxidating reductase activity, both of which are essential for normal beta-cell function. In conclusion, we suggest that an imbalance between these activities might be implicated in beta-cell dysregulation involved in certain pathological hyperinsulinic states.

Animals↗
PubMed2000

4-Hydroxyisoleucine: effects of synthetic and natural analogues on insulin secretion.

4-Hydroxyisoleucine, a peculiar amino acid extracted from fenugreek seeds and never found in mammalian tissues, exhibits interesting insulinotropic activity. To investigate the structural requirements for this stimulating effect, the insulinotropic activity of the major isomer (2S,3R,4S) of 4-hydroxyisoleucine, in the presence of 8. 3 mM glucose, was compared to that of (1) its minor isomer (2R,3R, 4S) (2) its lactone form, (3) classical structurally related amino acids, and (4) synthetic monomethylated analogues. In the isolated, ex vivo, perfused rat pancreas, only the major isomer of 4-hydroxyisoleucine (200 microM) potentiated insulin release. On incubated isolated rat islets, the threshold concentration for a significant increase (P<0.05) in insulin release was 200 microM for (2S,3R,4S) 4-hydroxyisoleucine, 500 microM for (2S,4R) and (2S,4S) gamma-hydroxynorvalines as well as (2S,3S) and (2S,3R) gamma-hydroxyvalines, and 1 mM or more for other congeners. In conclusion, the insulinotropic properties of 4-hydroxyisoleucine, in the micromolar range, are seen only in the presence of the linear major isoform; they also require carbon alpha in S-configuration, full methylation and carbon gamma-hydroxylation.

Animals↗
PubMed2000

Preproinsulin I and II mRNA expression in adult rat submandibular glands.

Mammalian salivary glands are known to produce a number of biologically active peptides. The aim of this study was to extend our previous results showing the presence of a biologically active insulin-like immunoreactive peptide in rat salivary glands. In rodents, where two nonallelic and functional insulin genes are expressed, the co-expression of both genes seems to be limited to beta-cells of pancreatic islets or to embryologic developmental processes. We have investigated the expression of insulin genes in rat submandibular glands and in a murine immortalized submandibular cell line, SCA-9. For this purpose, total RNAs were isolated and submitted to reverse transcription. The cDNAs obtained were amplified by a nested polymerase chain reaction using rat preproinsulin I and II primers. Our data show that both preproinsulin I and II mRNAs are expressed in adult rat submandibular glands as well as in the SCA-9 cell line. The identification of salivary gland rat preproinsulin I and II was confirmed by direct sequencing. These results provide, for the first time, evidence for the expression of both preproinsulin I and II mRNA in an extra-pancreatic tissue from adult rodents.

Animals↗
PubMed2000

Insulinotropic effect of Citrullus colocynthis fruit extracts.

Infusions of Citrullus colocynthis Schrad. (Cucurbitaceae) fruits are traditionally used as antidiabetic medication in Mediterranean countries, but to our knowledge no studies have been undertaken so far to determine the possible mechanisms involved in the antidiabetic properties of the fruit. The present study was designed to investigate whether these fruits possess insulinotropic effects. For this purpose, different extracts of Citrullus colocynthis seed components were obtained: RN II (crude extract), RN VI (hydro-alcoholic extract), RN X (purified extract) and RN XVII (beta-pyrazol-1-ylalanine), the major free amino acid present in the seeds. The insulin secretory effects of these different extracts were evaluated in vitro in the isolated rat pancreas and isolated rat islets in the presence of 8.3 mM glucose. All tested extracts, when perfused for 20 min at 0.1 mg/ml, immediately and significantly stimulated insulin secretion. This effect was transient. In addition, the purified extract (RN X) provoked a clear dose-dependent increase in insulin release from isolated islets. Moreover, a significant and persistant increase in pancreatic flow rate appeared during RN VI, RN X and RN XVII perfusions. In conclusion, our results show that different Citrullus colocynthis seed extracts have an insulinotropic effect which could at least partially account for the antidiabetic activities of these fruits.

Amino Acids↗
PubMed1999

4-Hydroxyisoleucine: experimental evidence of its insulinotropic and antidiabetic properties.

We have recently shown in vitro that 4-hydroxyisoleucine (4-OH-Ile), an amino acid extracted from fenugreek seeds, potentiates insulin secretion in a glucose-dependent manner. The present study was designed to investigate whether 4-OH-Ile could exert in vivo insulinotropic and antidiabetic properties. For this purpose, intravenous or oral glucose tolerance tests (IVGTTs and OGTTs, respectively) were performed not only in normal animals but also in a type II diabetes rat model. During IVGTT in normal rats or OGTT in normal dogs, 4-OH-Ile (18 mg/kg) improved glucose tolerance. The lactonic form of 4-OH-Ile was ineffective in normal rats. In non-insulin-dependent diabetic (NIDD) rats, a single intravenous administration of 4-OH-Ile (50 mg/kg) partially restored glucose-induced insulin response without affecting glucose tolerance; a 6-day subchronic administration of 4-OH-Ile (50 mg/kg, daily) reduced basal hyperglycemia, decreased basal insulinemia, and slightly, but significantly, improved glucose tolerance. In vitro, 4-OH-Ile (200 microM) potentiated glucose (16.7 mM)-induced insulin release from NIDD rat-isolated islets. So, the antidiabetic effects of 4-OH-Ile on NIDD rats result, at least in part, from a direct pancreatic B cell stimulation.

Acids↗
PubMed1998

Vanadyl treatment normalizes submandibular salivary gland insulin-like immunoreactivity in streptozotocin-diabetic rats.

Rat submandibular salivary glands (SSG) contain a compound displaying insulin-like immunoreactivity (ILI) and various biological activities of insulin. As SSG ILI levels were reported to be increased in streptozotocin (STZ)-induced diabetes but not normalized by a two-week insulin treatment, we decided to check whether another antidiabetic treatment, vanadyl sulphate (VOSO4), was able to regulate SSG ILI concentration. A short term (8 days) i.p. VOSO4 treatment (total dose = 1.3 mmol/kg) of rats made diabetic 8 days earlier by a single i.v. injection of STZ (60 mg/kg BW) was able to induce a long-term (4 weeks) correction of hyperglycemia while weight gain was re-established. In untreated diabetic animals (approximately -25%) and increased (approximately +175%) as compared to normal rats. Both parameters were normalized in VOSO4-treated diabetic rats.

Animals↗
PubMed1998

4-Hydroxyisoleucine: a novel amino acid potentiator of insulin secretion.

We report the characterization of a new insulinotropic compound, 4-hydroxyisoleucine. This amino acid has been extracted and purified from fenugreek seeds, which are known in traditional medicine for their antidiabetic properties. 4-Hydroxyisoleucine increases glucose-induced insulin release, in the concentration range of 100 micromol/l to 1 mmol/l, through a direct effect on isolated islets of Langerhans from both rats and humans. The stimulating effect of 4-hydroxyisoleucine was strictly glucose dependent; indeed, ineffective at low (3 mmol/l) or basal (5 mmol/l) glucose concentrations, the amino acid potentiated the insulin secretion induced by supranormal (6.6-16.7 mmol/l) concentrations of glucose. In addition, in the isolated perfused rat pancreas, we could show 1) that the pattern of insulin secretion induced by 4-hydroxyisoleucine was biphasic, 2) that this effect occurred in the absence of any change in pancreatic alpha- and delta-cell activity, and 3) that the more glucose concentration was increased, the more insulin response was amplified. Moreover, 4-hydroxyisoleucine did not interact with other agonists of insulin secretion (leucine, arginine, tolbutamide, glyceraldehyde). Therefore, we conclude that 4-hydroxyisoleucine insulinotropic activity might, at least in part, account for fenugreek seeds' antidiabetic properties. This secretagogue may be considered as a novel drug with potential interest for the treatment of NIDDM.

Animals↗
PubMed1998

Experimental NIDDM: development of a new model in adult rats administered streptozotocin and nicotinamide.

We took advantage of the partial protection exerted by suitable dosages of nicotinamide against the beta-cytotoxic effect of streptozotocin (STZ) to create a new experimental diabetic syndrome in adult rats that appears closer to NIDDM than other available animal models with regard to insulin responsiveness to glucose and sulfonylureas. Among the various dosages of nicotinamide tested in 3-month-old Wistar rats (100-350 mg/kg body wt), the dosage of 230 mg/kg, given intraperitoneally 15 min before STZ administration (65 mg/kg i.v.) yielded a maximum of animals with moderate and stable nonfasting hyperglycemia (155 +/- 3 vs. 121 +/- 3 mg/dl in controls; P < 0.05) and 40% preservation of pancreatic insulin stores. We also evaluated beta-cell function both in vitro and in vivo 4-9 weeks after inducing diabetes. In the isolated perfused pancreas, insulin response to glucose elevation (5-11 mmol/l) was clearly present, although significantly reduced with respect to controls (P < 0.01). Moreover, the insulin response to tolbutamide (0.19 mmol/l) was similar to that observed in normal pancreases. Perfused pancreases from diabetic animals also exhibited a striking hypersensitivity to arginine infusion (7 mmol/l). In rats administered STZ plus nicotinamide, intravenous glucose tolerance tests revealed clear abnormalities in glucose tolerance and insulin responsiveness, which were interestingly reversed by tolbutamide administration (40 mg/kg i.v.). In conclusion, this novel NIDDM syndrome with reduced pancreatic insulin stores, which is similar to human NIDDM in that it has a significant response to glucose (although abnormal in kinetics) and preserved sensitivity to tolbutamide, may provide a particularly advantageous tool for pharmacological investigations of new insulinotropic agents.

Animals↗
PubMed1997

Antazoline increases insulin secretion and improves glucose tolerance in rats and dogs.

In vivo effects of an imidazoline devoid of alpha2-adrenoceptor antagonistic properties, antazoline, on insulin secretion and glycemia were investigated both in fasted rats and dogs. In both species, antazoline (1.5 mg/kg i.v.) transiently increased insulinemia without affecting basal plasma glucose levels. In contrast, during an i.v. glucose tolerance test, antazoline markedly potentiated insulin release and thus increased the glucose disappearance rate. In rats, during an oral glucose tolerance test, the intragastric administration of antazoline (1.5 mg/kg) clearly enhanced insulin secretion and reduced hyperglycemia. In dogs provided with a venous pancreatico-duodenal bypass, antazoline (0.5 mg/kg i.v.) induced an immediate and transient increase in insulin and somatostatin but not in glucagon pancreatico-duodenal outputs. In conclusion, intravenously and orally administered, the imidazoline antazoline is able to stimulate insulin secretion in vivo and improve glucose tolerance. The imidazoline compounds could therefore have a potential therapeutic relevance as new antihyperglycemic insulinotropic agents.

Animals↗
PubMed1997

Mechanisms involved in the effect of nitric oxide synthase inhibition on L-arginine-induced insulin secretion.

1. A constitutive nitric oxide synthase (NOSc) pathway negatively controls L-arginine-stimulated insulin release by pancreatic beta cells. We investigated the effect of glucose on this mechanism and whether it could be accounted for by nitric oxide production. 2. NOSc was inhibited by N omega-nitro-L-arginine methyl ester (L-NAME), and sodium nitroprusside (SNP) was used as a palliative NO donor to test whether the effects of L-NAME resulted from decreased NO production. 3. In the rat isolated perfused pancreas, L-NAME (5 mM) strongly potentiated L-arginine (5 mM)-induced insulin secretion at 5 mM glucose, but L-arginine and L-NAME exerted only additive effects at 8.3 mM glucose. At 11 mM glucose, L-NAME significantly inhibited L-arginine-induced insulin secretion. Similar data were obtained in rat isolated islets. 4. At high concentrations (3 and 300 microM), SNP increased the potentiation of arginine-induced insulin output by L-NAME, but not at lower concentrations (3 or 30 nM). 5. L-Arginine (5 mM) and L-ornithine (5 mM) in the presence of 5 mM glucose induced monophasic beta cell responses which were both significantly reduced by SNP at 3 nM but not at 30 nM; in contrast, the L-ornithine effect was significantly increased by SNP at 3 microM. 6. Simultaneous treatment with L-ornithine and L-arginine provoked a biphasic insulin response. 7. At 5 mM glucose, L-NAME (5 mM) did not affect the L-ornithine secretory effect, but the amino acid strongly potentiated the alteration by L-NAME of L-arginine-induced insulin secretion. 8. L-Citrulline (5 mM) significantly reduced the second phase of the insulin response to L-NAME (5 mM) + L-arginine (5 mM) and to L-NAME + L-arginine + SNP 3 microM. 9. The intermediate in NO biosynthesis, NG-hydroxy-L-arginine (150-300 microM) strongly counteracted the potentiation by L-NAME of the secretory effect of L-arginine at 5 mM glucose. 10. We conclude that the potentiation of L-arginine-induced insulin secretion resulting from the blockade of NOSc activity in the presence of a basal glucose concentration (1) is strongly modulated by higher glucose concentrations, (2) is not due to decreased NO production but (3) is probably accounted for by decreased levels of NG-hydroxy-L-arginine or L-citrulline, resulting in the attenuation of an inhibitory effect on arginase activity.

Animals↗
PubMed1996

Vanadyl sulphate differently influences insulin response to glucose in isolated pancreas of normal rats after in vivo or in vitro exposure.

The effect of the antidiabetic agent vanadyl sulphate (VOSO4) on the endocrine pancreas function of normal rats was studied using the isolated pancreas preparation. A short-term (8 days) i.p. treatment (15 mg/kg per day) resulted in attenuation of high glucose-stimulated insulin release, at day 9 but also at days 19, i.e., after full recovery of appetite and weight, while blood and pancreas vanadium concentrations were still elevated. Six months of oral VOSO4 treatment (0.75 mg/ml in drinking water) resulted in elevated vanadium concentrations while glucose-stimulated insulin release was attenuated as compared to pair-fed animals. Conversely, when directly perfused in pancreas, VOSO4 potentiated glucose-stimulated insulin release. These apparently opposite effects may be related to the ability of VOSO4 to exert both peripheral insulinomimetic effects-leading to chronic reduction in insulin demand-, and a direct pancreatic insulinotropic activity.

Administration, Oral↗
PubMed1996

Pancreastatin modulates glucose-stimulated insulin secretion from the perfused rat pancreas.

Pancreastatin is known to be produced in islet B cells and to inhibit insulin secretion. In this study, we examined whether the peptide affects insulin secretion from the perfused rat pancreas during raising or lowering the glucose concentration within the physiological range. We found that synthetic porcine pancreastatin (15 nmol L-1) significantly inhibited the first phase (5 min) of insulin release induced by raising the glucose concentration from 4.2 to 8.3 mmol L-1 (P < 0.05) without affecting the second phase. Furthermore, the fall in insulin secretion induced by lowering the glucose concentration from 8.3 to 5.5 mmol L-1 was significantly exaggerated in presence of pancreastatin during the first 5 min (P < 0.05). In contrast, pancreastatin did not affect the inhibition of insulin secretion induced by either the alpha 2-adrenoceptor agonist, clonidine (2 nmol L-1), or the P1-purinoceptor (A1-subtype) agonist, N6 (+)-phenylisopropyladenosine (D-PIA) (1.65 mumol L-1). In conclusion, our results show that pancreastatin is a modulator of the early changes in insulin secretion after increase or decrease of the glucose concentration within the physiological range. This suggests that pancreastatin is a modulator of glucose-stimulated insulin secretion.

Adrenergic alpha-Agonists↗
PubMed1995

Effect of n-hexacosanol on insulin secretion in the rat.

n-Hexacosanol, a long-chain saturated fatty alcohol extracted from Hygrophyla erecta Hochr., has been recently shown to exert neurotrophic properties on central neurons and to stimulate phagocytosis in macrophages. The present work was designed to investigate the effects of hexacosanol on stimulated insulin secretion in vivo and in vitro. In anaesthetized rats, hexacosanol (2 mg/kg i.p.) induced a reduction of the insulin response to an intravenous glucose tolerance test (0.3 g/kg) with a consequent increase in hyperglycaemia. In vitro, in the isolated perfused pancreas, hexacosanol at the concentration of 10(-7) M clearly reduced the two phases of glucose-induced insulin secretion. At the higher concentration (10(-5) M), hexacosanol was no longer able to exert an inhibition of glucose-induced insulin release; surprisingly a stimulating effect occurred which was of the same magnitude as in control experiments with Tween alone, at the concentration used to dissolve hexacosanol. In isolated perifused islets, 22 mM glucose-stimulated insulin release was also inhibited by hexacosanol at the concentrations of 10(-9) M and 10(-7) M, but not at 10(-5) M. In contrast, insulin secretion induced by arginine (20 mM) was not affected by the different concentrations of hexacosanol. It is concluded that n-hexacosanol at 10(-9) M and 10(-7) M exerts an inhibitory effect on insulin secretion stimulated by glucose in vivo and in vitro in the rat, suggesting a direct effect on islets of Langerhans.

Analysis of Variance↗
PubMed1995

Alterations of insulin response to different beta cell secretagogues and pancreatic vascular resistance induced by N omega-nitro-L-arginine methyl ester.

1. We studied a possible interplay of pancreatic NO synthase activity on insulin secretion induced by different beta cell secretagogues and also on pancreatic vascular bed resistance. 2. This study was performed in the isolated perfused pancreas of the rat. Blockage of NO synthase was achieved with Nw-nitro-L-arginine methyl ester (L-NAME); The specificity of the antagonist was checked by using its D-enantiomer as well as by substitutive treatments with sodium nitroprusside (SNP) as a NO donor in studies of glucose-induced insulin secretion. 3. Arginine (5 mM) induced a monophasic response which was, in the presence of L-NAME at equimolar concentration, very strongly potentiated and converted into a 13 times higher biphasic one. D-NAME (5 mM) was only able to induce a 3 times higher response, but provoked a similar vasoconstrictor effect. 4. The small biphasic insulin secretion induced by L-leucine (5 mM) was also strongly enhanced, by 8 times, in the presence of L-NAME (5 mM) vs 2 times in the presence of D-NAME (5 mM). 5. beta cell responses to KCl (5 mM) and tolbutamide (0.185 mM) were only slight increased by L-NAME (5 mM) to values not far from the sum of the effects of L-NAME and of the two drugs alone. D-NAME (5 mM) was totally ineffective on the actions of both secretagogues. 6. L-NAME, infused 15 min before and during a rise in glucose concentration from 5 to 11 mM, was able in the low millimolar range (0.1-0.5 mM) to blunt the classical biphasic pattern of beta cell response to glucose and, at 5 mM, to convert it into a significantly greater monophasic one. In contrast, D-NAME (5 mM) was unable to induce similar effects. 7. SNP alone at 3 microM was ineffective but at 30 microM substantially reduced to second phase of insulin response to glucose; however, at both concentrations the NO donor partly reversed alterations in insulin secretion caused by L-NAME (5 mM) and restored a biphasic response.

Analysis of Variance↗
PubMed1995

Biological activity of immunoreactive insulin-like activity extracted from rat submandibular gland.

Earlier studies indicate the presence of an insulin-like immunoreactivity (ILI) in rat submandibular salivary glands (SSG). Previous observations also showed that streptozotocin (STZ)-induced diabetes was accompanied by an increase in SSG ILI concentrations. In the present work we studied the effect of SSG ILI from normal and STZ diabetic rats (ILI-N and ILI-D, respectively) on insulin receptor binding and function in LMH cell line. ILI-N and ILI-D inhibited 125I-insulin binding to intact cells and wheat germ agglutinin (WGA)-purified insulin receptors with a high affinity. Furthermore, ILI-N and ILI-D activated, although weakly, the beta-subunit autophosphorylation of solubilized and WGA-purified insulin receptors. An ATP hydrolytic activity was present in ILI-N and, to a greater extent, in ILI-D extracts, which can at least in part explain their low potency for activating autophosphorylation and kinase activity of insulin receptors in vitro. However, after ILI treatment of intact cells and immunoprecipitation of insulin receptors, ILI induced a dose-dependent tyrosine phosphorylation of the insulin receptor beta-subunit. Finally, ILI-N and ILI-D stimulated amino acid uptake and lipogenesis in LMH cells. These findings suggest that SSG ILI is biologically active and can participate in metabolic regulations.

Amino Acids↗
PubMed1994

Effects of imidazolines and derivatives on insulin secretion and vascular resistance in perfused rat pancreas.

The effects of imidazolines and derivatives were studied on insulin secretion and vascular resistance in the isolated perfused rat pancreas. On insulin secretion, two imidazoline alpha 2-adrenoceptor antagonists, efaroxan (1-100 microM) and RX821002 (10 microM), had a stimulating response; however, idazoxan, like the non-imidazoline alpha 2-adrenoceptor antagonist yohimbine, was ineffective at 10 microM. The oxazoline rilmenidine with alpha 2-adrenergic activity at 10 microM), an imidazoline devoid of alpha 2-adrenergic activity, also had an insulin-releasing effect. On pancreatic vessels, all imidazolines tested (efaroxan, RX821002, antazoline and idazoxan), in contrast to yohimbine, induced vasoconstriction. Rilmenidine did not have a vasoconstrictor effect after blockade of alpha 2-adrenoceptors. Furthermore, the efaroxan-induced insulin release or vasoconstriction was not affected by the blockade of alpha 2- and alpha 1-adrenoceptors. This study shows that imidazolines and derivatives are able to stimulate insulin release and induce vasoconstriction in the rat pancreas. These effects cannot be ascribed to an interaction with alpha-adrenoceptors but may involve different types of imidazoline sites.

Adrenergic alpha-1 Receptor Antagonists↗