Search Results

You are looking at 101 - 110 of 788 items for :

  • "insulin secretion" x
  • Refine by Access: All content x
Clear All
Free access

ML Villanueva-Penacarrillo, J Cancelas, F de Miguel, A Redondo, A Valin, I Valverde, and P Esbrit

Parathyroid hormone (PTH)-related protein (PTHrP) is present in the pancreatic islet. Recent data in transgenic mice suggest that PTHrP might modulate islet mass and insulin secretion. In the present study, we assessed the effect of the N-terminal PTH-like region of PTHrP on DNA synthesis in isolated rat islets. PTHrP (1-34), between 1 pM and 10 nM, for 48 h stimulated []thymidine incorporation into rat islets. This effect was maximally induced, about 2.5-fold over control, by 10 pM of this peptide, decreasing thereafter. In contrast, PTHrP (38-64) amide or PTHrP (107-139) were ineffective in increasing DNA synthesis in islets. Using reverse transcription followed by PCR, we confirmed that rat islets express PTHrP and the type I PTH/PTHrP receptor. Addition of a neutralizing anti-PTHrP antibody to the incubation medium of proliferating islets decreased islet DNA synthesis by 30%. The effect of a submaximal dose (30 pM) of PTHrP (1-34) on DNA synthesis in rat islets was abolished by 25 nM bisindolylmaleimide I, a protein kinase C (PKC) inhibitor, but not by 25 microM adenosine 3',5'-cyclic monophosphorothioate, Rp-isomer, a protein kinase A inhibitor. Moreover, 100 nM phorbol-12-myristate-13-acetate for 48 h also increased DNA synthesis 2-fold over controls in islets. PTHrP (1-34), at 100 nM, in contrast to 50 microM forskolin or 10 mM NaF, failed to affect adenylate cyclase activity in islet membranes. PTHrP, at 30 pM, was also found to increase 2-fold insulin released into the islet-conditioned medium within 24-48 h. Our results suggest that PTHrP is a modulator of pancreatic islet growth and/or function by a PKC-mediated mechanism.

Free access

H Mosen, A Salehi, and I Lundquist

The mechanism of nutrient-evoked insulin release is clearly complex. One part of that mechanism is postulated to be the activation of the glycogenolytic enzyme acid glucan-1,4-alpha-glucosidase. As nitric oxide (NO) has been found to be a potent inhibitor of glucose-stimulated insulin secretion, we have now investigated a possible influence of exogenous NO and inhibition of endogenous NO production on islet acid glucan-1,4-alpha-glucosidase activity in relation to insulin release stimulated by glucose and l-arginine. In isolated islets, NO derived from the intracellular NO donor hydroxylamine inhibited the activation of acid glucan-1, 4-alpha-glucosidase and its isoform acid alpha-glucosidase in parallel with inhibition of glucose-stimulated insulin release. In comparison, other lysosomal enzymes were largely unaffected. Similarly, the spontaneous NO donor sodium nitroprusside, as well as NO gas, when added to islet homogenates, suppressed the activities of these acid alpha-glucosidehydrolases and, to a lesser extent, the activities of other lysosomal enzymes. Finally, in the presence of the NO synthase inhibitor N(G)-nitro-l-arginine methyl ester, insulin release from isolated islets stimulated by glucose or l-arginine was markedly potentiated in parallel with an accompanying increase in the activities of acid glucan-1,4-alpha-glucosidase and acid alpha-glucosidase. Other lysosomal enzymes and neutral alpha-glucosidase were not influenced. We propose that an important inhibitory effect of NO on the insulin secretory processes stimulated by glucose and l-arginine is exerted via inactivation of islet acid glucan-1,4-alpha-glucosidase, a putative key enzyme in nutrient-stimulated insulin release.

Restricted access

S C Blair, I D Caterson, and G J Cooney

Abstract

The effect of adrenalectomy (ADX) on glucose tolerance and insulin secretion was examined in conscious mice made obese by a single injection of gold thioglucose (GTG). To facilitate such a study a chronic jugular catheter was implanted into the mice at the time of performing the ADX or sham-ADX. One week after ADX, the body weight (GTG-obese+sham-ADX, 35·6 ± 0·6 g; GTG-obese+ADX, 33·1 ± 0·6 g; P<0·05) and glycogen content of the liver (GTG-obese+sham-ADX, 2·4 ± 0·2 μmol/liver; GTG-obese+ADX, 1·6 ± 0·1 μmol/liver; P<0·05) of GTG-injected mice were reduced. Plasma glucose concentrations, in both the overnight fasted state and in response to an intravenous glucose load were also reduced following ADX of GTG-obese mice, but not to the level of the sham-ADX control mice. However, ADX completely normalized plasma insulin concentrations in both the basal state and also in response to a glucose load, as indicated by the finding that the integrated insulin secretory response of the ADX GTG-obese mice was not different from that of sham-ADX control mice (control+sham-ADX, 192 ± 5 min.μU/ml; GTG-obese+ADX, 196 ± 10 min.μU/ml). The effects of ADX on carbohydrate metabolism were not restricted to GTG-injected mice, as ADX of control mice decreased fasting plasma glucose levels and reduced liver glycogen and plasma insulin concentrations. The normalization of insulin release in ADX GTG-obese mice occurred while these mice were still obese and glucose intolerant. This suggests that the decreased insulin release was not due solely to an ADX-induced improvement in insulin sensitivity and/or weight loss. Removal of central glucocorticoid effects on the parasympathetic stimulation of insulin release may play a role in the reduced insulin release observed after ADX of obese and control mice, although peripheral effects of glucocorticoid deficiency on glycogen synthesis in the liver may also influence whole animal glucose homeostasis.

Journal of Endocrinology (1996) 148, 391–398

Restricted access

F. Takao, S. Kagawa, K. Sakamoto, and A. Matsuoka

ABSTRACT

The effect of maternal hyperglycaemia on the function of neonatal B cells was examined using a perifusion technique in pancreatic monolayer cultures of neonatal rats from normoglycaemic mothers (C), and those made slightly hyperglycaemic (SH) and highly hyperglycaemic (HH) by injection of streptozotocin. Monolayer cultures were kept for 7 days in medium containing 5·5 mmol glucose/l plus 1 mmol 2-deoxy-glucose/l. On day 0, B cells in the C group responded to 16·7 mmol glucose/l, 10 mmol leucine/l and 10 mmol 2-ketoisocaproate/l in a monophasic fashion with no significant rise in the second phase. However, compared with the C group, a significant increase in the second-phase secretion in response to glucose and 2-ketoisocaproate was observed in the SH group, although there was no difference in the first-phase secretion. In the HH group the insulin secretion was lower in the first phase but not in the second phase. After culture for 7 days, B cells in the C group showed a biphasic response to the secretagogues, with a great increase in the second-phase secretion. In the SH group, the second phase of insulin secretion was increased but the increment was far less than that in the C group. The secretory response was remarkably low in the HH group compared with other groups. From these results, we conclude that at an early stage of culture slight maternal hyperglycaemia causes a hypersensitivity of neonatal B cells but impairs the normal development of the function of B cells during culture, and that high hyperglycaemia results in impaired insulin secretion throughout the whole period of culture studied.

J. Endocr. (1988) 119, 493–499

Restricted access

N H McClenaghan, C R Barnett, F P M O'Harte, and P R Flatt

Abstract

The effects of different classes of amino acids known to be transported and utilized by pancreatic B-cells were examined using the novel glucose-responsive pancreatic B-cell line, BRIN-BD11. Amino acids tested included α-aminoisobutyric acid, l-alanine, l-arginine, l-glutamine, glycine, l-leucine, l-lysine, l-proline and l-serine. At non-stimulatory (1·1 mmol/l) glucose, acute incubations with either 1 or 10 mmol/l amino acid evoked 1·3- to 4·7-fold increases of insulin release. Raising glucose to 16·7 mmol/l enhanced the effects of all amino acids except l-glutamine, and increased insulin output at 10 mmol/l compared with 1 mmol/l amino acid. Glyceraldehyde (10 mmol/l) also served to promote 10 mmol/l amino acid-induced insulin secretion with the exceptions of l-arginine, glycine, l-lysine and l-proline. At 16·7 mmol/l glucose, diazoxide (300 μmol/l) significantly decreased the secretory response to all amino acids except l-glutamine. Likewise, verapamil (20 μmol/l) or depletion of extracellular Ca2+ reduced insulin output indicating the importance of Ca2+ influx in the actions of amino acids. These data indicate that BRIN-BD11 cells transport and utilize amino acids, acting in association with glycolysis, K+-ATP channels and/or voltage-dependent Ca2+ channels to promote Ca2+ influx and insulin secretion. The response of BRIN-BD11 cells to glucose and amino acids indicates that this is a useful cell line for future research on the mechanisms of nutrient regulation of insulin secretion.

Journal of Endocrinology (1996) 151, 349–357

Free access

A Ribeiro-de-Oliveira Jr, RM Guerra, RB Foscolo, U Marubayashi, AM Reis, and CC Coimbra

Neurocytoglucopenia has been reported to increase both parasympathetic and sympathetic tone with a predominant effect on the latter, which accounts for the major effect of plasma hyperglycemia and the inhibition of insulin secretion. The aim of this study was to determine the effects of chronic treatment with bromocriptine (0.4 mg/100 g body wt per day), a potent sympatholytic D(2)-dopaminergic agonist, on hyperglycemia and insulin secretion in response to neurocytoglucopenia induced by 2-deoxy-d-glucose (2DG). After 2 weeks of bromocriptine treatment the animals, freely moving in their cages, were submitted to 2DG administration (50 mg/100 g body wt) via atrial catheter infusion. After 2DG infusion, the plasma prolactin of vehicle-treated (VEH) rats increased rapidly, reaching a peak at 10 min (34.3+/-7.6 ng/ml; P<0.01). In contrast, 2DG infusion failed to induce any significant change in the plasma prolactin levels of bromocriptine-treated (BR) rats. BR rats showed higher resting glucose levels than control rats (8.2+/-0.28 mM (BR) vs 6.0+/-0.18 mM (VEH); P<0.01). However, the hyperglycemic response of BR rats to 2DG injection was 30% lower than that of VEH rats (P<0.05). BR rats also showed a rapid rise in plasma insulin levels reaching a peak at 30 min after 2DG injection (243% higher than basal values; P<0.01). This increased rise in the insulin response to neurocytoglucopenia of BR rats was blocked by previous intravenous injection of atropine methyl nitrate (0.2 mg/100 g body wt). The present results suggest that chronic treatment with bromocriptine determines a strong increase in the parasympathetic tone response to neurocytoglucopenia, which is responsible for the higher stimulation of insulin secretion observed in BR rats. The data also provide further evidence that D(2)-dopaminergic agonist can block neurocytoglucopenia-induced prolactin release.

Free access

Eva Kassi and Athanasios G Papavassiliou

(incremental immunoreactive insulin over incremental plasma glucose, 0–30 min after 75 g oral glucose loading, indicating the early phase insulin secretion). Subsequently, the same research team ( Sakamoto et al . 2000 ) administered menaquinone-4 (90 mg

Restricted access

N. Billingham, Anne Beloff-Chain, and M. A. Cawthorne

The influence of plasma from genetically obese (ob/ob) and lean (+/+) mice on insulin secretion has been studied by perifusion of collagenase-prepared pancreatic islets maintained for 48 h in culture. Insulin secretion was measured at 2-min intervals and plasma from the ob/ob mice not from the +/+ mice rapidly stimulated insulin release, reaching a maximum in 2–4 min and falling to basal levels in about 10 min. Experimental evidence is given indicating that the plasma insulin secretagogue is identical to β-cell-trophin, a peptide of the pituitary pars intermedia which stimulates insulin secretion. The evidence is based on (1) the antigenic properties of the peptides (both cross-react with a -COOH terminal ACTH antiserum raised to the 17–39 moiety of ACTH), (2) identical chromatographic separation on Biogel columns and on reverse-phase high pressure liquid chromatography and (3) the similarity of their insulin releasing action from perifused islets.

Restricted access

J Vadakekalam, M E Rabaglia, and S A Metz

Abstract

Glucose can augment insulin secretion independently of K+ channel closure, provided cytoplasmic free Ca2+ concentration is elevated. A role for phospholipase C (PLC) in this phenomenon has been both claimed and refuted. Recently, we have shown a role for GTP in the secretory effect of glucose as well as in glucose-induced PLC activation, using islets pre-treated with GTP synthesis inhibitors such as mycophenolic acid (MPA). Therefore, in the current studies, we examined first, whether glucose augments Ca2+-induced PLC activation and second, whether GTP is required for this effect, when K+(ATP) channels are kept open using diazoxide. Isolated rat islets pre-labeled with [3H]myo-inositol were studied with or without first priming with glucose. There was a 98% greater augmentation of insulin secretion by 16·7 mm glucose (in the presence of diazoxide and 40 mm K+) in primed islets; however, the ability of high glucose to augment PLC activity bore no relationship to the secretory response. MPA markedly inhibited PLC in both conditions; however, insulin secretion was only inhibited (by 46%) in primed islets. None of these differences were attributable to alterations in labeling of phosphoinositides or levels of GTP or ATP. These data indicate that an adequate level of GTP is critical for glucose's potentiation of Ca2+-induced insulin secretion in primed islets but that PLC activation can clearly be dissociated from insulin secretion and therefore cannot be the major cause of glucose's augmentation of Ca2+-induced insulin secretion.

Journal of Endocrinology (1997) 153, 61–71

Free access

EP Araujo, ME Amaral, E Filiputti, CT De Souza, TL Laurito, VD Augusto, MJ Saad, AC Boschero, LA Velloso, and EM Carneiro

Autocrine and paracrine insulin signaling may participate in the fine control of insulin secretion. In the present study, tissue distribution and protein amounts of the insulin receptor and its major substrates, insulin receptor substrate (IRS)-1 and IRS-2, were evaluated in a model of impaired glucose-induced insulin secretion, the protein-deficient rat. Immunoblot and RT-PCR studies showed that the insulin receptor and IRS-2 expression are increased, whilst IRS-1 protein and mRNA contents are decreased in pancreatic islets of protein-deficient rats. Immunohistochemical studies revealed that the insulin receptor and IRS-1 and -2 are present in the great majority of islet cells; however, the greatest staining was localized at the periphery, suggesting a co-localization with non-insulin-secreting cells. Exogenous insulin stimulation of isolated islets promoted higher insulin receptor and IRS-1 and -2 tyrosine phosphorylation in islets from protein-deficient rats, as compared with controls. Moreover, insulin-induced IRS-1- and IRS-2-associated phosphatidylinositol 3-kinase activity are increased in islets of protein-deficient rats. The reduction of IRS-1 and IRS-2 protein expression in islets isolated from protein-deficient rats by the use of antisense IRS-1 or IRS-2 phosphorthioate-modified oligonucleotides partially restored glucose-induced insulin secretion. Thus, the impairment of insulin cell signaling through members of the IRS family of proteins in isolated rat pancreatic islets improves glucose-induced insulin secretion. The present data reinforced the role of insulin paracrine and autocrine signaling in the control of its own secretion.