Islet glucan-1,4-α-glucosidase: differential influence on insulin secretion induced by glucose and isobutylmethylxanthine in mice

1993 ◽  
Vol 138 (3) ◽  
pp. 391-400 ◽  
Author(s):  
A. Salehi ◽  
I. Lundquist
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Marked Reduction ◽  
Insulin Response ◽  
Indirect Evidence ◽  
Secretory Response ◽  
Isolated Pancreatic Islets ◽  
Enzyme Replacement ◽  
Insulin Secretory Response

ABSTRACT In previous in-vivo studies we have presented indirect evidence for the involvement of islet acid glucan-1,4-α-glucosidase (acid amyloglucosidase), a lysosomal glycogen-hydrolysing enzyme, in certain insulin secretory processes. In the present combined in-vitro and in-vivo investigation, we studied whether differential changes in islet acid amyloglucosidase activity were related to the insulin secretory response induced by two mechanistically different secretagogues, glucose and isobutylmethylxanthine (IBMX). It was observed that addition of the selective α-glucosidehydrolase inhibitor emiglitate (1 mmol/l) to isolated pancreatic islets resulted in a marked reduction of glucose-induced insulin release. This was accompanied by a pronounced suppression of islet activities of acid amyloglucosidase and acid α-glucosidase, whereas other lysosomal enzyme activities, such as acid phosphatase and N-acetyl-β-d-glucosaminidase, were unaffected. Furthermore, islets first incubated with emiglitate in the presence of high (16·7 mmol/l) glucose released less insulin than untreated controls in response to glucose in a second incubation period in the absence of emiglitate. In contrast, IBMX-induced insulin release was not influenced by emiglitate although accompanied by a marked reduction of islet activities of all three α-glucosidehydrolases. Basal insulin secretion (1 mmol glucose/1) was unaffected in the presence of emiglitate. In-vivo pretreatment of mice with highly purified fungal amyloglucosidase ('enzyme replacement'), a procedure known to increase islet amyloglucosidase activity, resulted in a greatly enhanced insulin secretory response to an i.v. glucose load. The increase in insulin release was accompanied by a markedly improved glucose tolerance curve in these animals. In contrast, enzyme pretreatment did not influence the insulin response or the blood glucose levels after an i.v. injection of IBMX. The data lend further support to our hypothesis that islet acid amyloglucosidase is involved in the multifactorial insulin secretory processes induced by glucose but not in those involving direct activation of the cyclic AMP system. The results also indicate separate, or at least partially separate, pathways for insulin release induced by glucose and IBMX. Journal of Endocrinology (1993) 138, 391–400

Ca2+ deficiency, selective alpha-glucosidehydrolase inhibition, and insulin secretion

1993 ◽  
Vol 265 (1) ◽  
pp. E1-E9 ◽  
Author(s):  
A. Salehi ◽  
I. Lundquist
Keyword(s):  
Insulin Secretion ◽  
Acid Phosphatase ◽  
Insulin Release ◽  
Insulin Response ◽  
Selective Inhibition ◽  
Half Maximal Effective Concentration ◽  
Insulin Secretory Response ◽  
Dose Dependent ◽  
Alpha Glucosidase

We investigated the relation between activities of islet glycogenolytic alpha-glucosidehydrolases and insulin secretion induced by glucose and 3-isobutyl-1-methylxanthine (IBMX) by means of suppressing 1) insulin release (Ca2+ deficiency) and 2) islet alpha-glucosidehydrolase activity (selective inhibition by the deoxynojirimycin derivative miglitol). Additionally, the in vivo insulin response to both secretagogues was examined. We observed that, similar to glucose-induced insulin release, islet glycogenolytic hydrolases (acid amyloglucosidase, acid alpha-glucosidase) were highly Ca2+ dependent. Acid phosphatase, N-acetyl-beta-D-glucosaminidase, or neutral alpha-glucosidase (endoplasmic reticulum) was not influenced by Ca2+ deficiency. In Ca2+ deficiency IBMX-induced insulin release was unaffected and was accompanied by reduced activities of islet alpha-glucosidehydrolases. Miglitol strongly inhibited glucose-induced insulin release concomitant with a marked suppression of islet alpha-glucosidehydrolase activities. Direct addition of miglitol to islet homogenates suppressed acid amyloglucosidase [half-maximal effective concentration (EC50) approximately 10(-6) M] and acid alpha-glucosidase. Acid phosphatase and N-acetyl-beta-D-glucosaminidase were unaffected. The miglitol-induced inhibition of glucose-stimulated insulin release was dose dependent (EC50 approximately 10(-6) M) and displayed a remarkable parallelism with the inhibition curve for acid amyloglucosidase. The in vivo insulin secretory response to glucose was markedly reduced in dystrophic mice (low amyloglucosidase), whereas the response to IBMX was unaffected. In summary, islet glycogenolytic hydrolases are Ca2+ dependent, and acid amyloglucosidase is directly involved in the multifactorial process of glucose-induced insulin release. In contrast the mechanisms of IBMX-stimulated insulin secretion operate independently of these enzymes. The effects of miglitol, a drug currently used in diabetes therapy, deserves further investigation.

scholarly journals The possible mechanisms by which phanoside stimulates insulin secretion from rat islets

2007 ◽  
Vol 192 (2) ◽  
pp. 389-394 ◽  
Author(s):  
Nguyen Khanh Hoa ◽  
Åke Norberg ◽  
Rannar Sillard ◽  
Dao Van Phan ◽  
Nguyen Duy Thuan ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
B Cells ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Pertussis Toxin ◽  
Insulin Response ◽  
Gk Rat ◽  
Isolated Pancreatic Islets ◽  
Gk Rats ◽  
Rat Islets

We recently showed that phanoside, a gypenoside isolated from the plant Gynostemma pentaphyllum, stimulates insulin secretion from rat pancreatic islets. To study the mechanisms by which phanoside stimulates insulin secretion. Isolated pancreatic islets of normal Wistar (W) rats and spontaneously diabetic Goto-Kakizaki (GK) rats were batch incubated or perifused. At both 3.3 and 16.7 mM glucose, phanoside stimulated insulin secretion several fold in both W and diabetic GK rat islets. In perifusion of W islets, phanoside (75 and 150 μM) dose dependently increased insulin secretion that returned to basal levels when phanoside was omitted. When W rat islets were incubated at 3.3 mM glucose with 150 μM phanoside and 0.25 mM diazoxide to keep K-ATP channels open, insulin secretion was similar to that in islets incubated in 150 μM phanoside alone. At 16.7 mM glucose, phanoside-stimulated insulin secretion was reduced in the presence of 0.25 mM diazoxide (P<0.01). In W islets depolarized by 50 mM KCl and with diazoxide, phanoside stimulated insulin release twofold at 3.3 mM glucose but did not further increase the release at 16.7 mM glucose. When using nimodipine to block L-type Ca2+ channels in B-cells, phanoside-induced insulin secretion was unaffected at 3.3 mM glucose but decreased at 16.7 mM glucose (P<0.01). Pretreatment of islets with pertussis toxin to inhibit exocytotic Ge-protein did not affect insulin response to 150 μM phanoside. Phanoside stimulated insulin secretion from Wand GK rat islets. This effect seems to be exerted distal to K-ATP channels and L-type Ca2+ channels, which is on the exocytotic machinery of the B-cells.

Involvement of capsaicin-sensitive nerves in regulation of insulin secretion and glucose tolerance in conscious mice

1994 ◽  
Vol 267 (4) ◽  
pp. R1071-R1077 ◽  
Author(s):  
S. Karlsson ◽  
A. J. Scheurink ◽  
A. B. Steffens ◽  
B. Ahren
Keyword(s):  
Insulin Secretion ◽  
Glucose Tolerance ◽  
Insulin Response ◽  
Secretory Response ◽  
Sensory Nerves ◽  
Plasma Norepinephrine ◽  
Plasma Catecholamine ◽  
Intravenous Glucose ◽  
The Impact ◽  
Insulin Secretory Response

The impact of sensory nerves in glucose-stimulated insulin secretion and glucose tolerance was investigated in conscious mice treated neonatally with either capsaicin (Cap) or vehicle (Veh). At 10-12 wk after Cap, both the early (1 min) insulin secretory response to intravenous glucose (2.8 mmol/kg) (by 67%) and glucose elimination were potentiated (P < 0.05). In contrast, basal insulin, glucagon, and glucose were not affected by Cap. Plasma norepinephrine and epinephrine levels did not differ between Cap- and Veh-treated animals, whereas the increase in plasma insulin levels normally induced by alpha-adrenoceptor blockade by phentolamine was absent after Cap treatment. In isolated islets, the insulin secretory response to glucose (20 mmol/l), carbachol (0.1 mmol/l), or phentolamine (0.5 mmol/l) was not affected after Cap. It is concluded that sensory denervation by Cap results in increased glucose tolerance, which is in part because of a potentiated early insulin response to glucose. This potentiation does not seem secondary to altered plasma catecholamine levels or to altered islet secretory capacity. The results suggest rather that Cap-sensitive nerves, by a local effector function and/or as the afferent loop of a neural reflex, exert inhibitory influences on insulin secretion.

An effect of hyposmolarity on insulin release in vitro

1975 ◽  
Vol 228 (3) ◽  
pp. 706-713 ◽  
Author(s):  
WG Blackard ◽  
M Kikuchi ◽  
A Rabinovitch ◽  
AE Renold
Keyword(s):  
Insulin Secretion ◽  
Calcium Concentration ◽  
Insulin Response ◽  
Secretory Response ◽  
Calcium Gradient ◽  
Blocking Agents ◽  
Medium Osmolarity ◽  
Pump Activity ◽  
Insulin Secretory Response

An abrupt reduction of medium osmolarity by as little as 20 mosM evoked a discrete short-lived insulin secretory response from perifused chopped pancreas or isolated islets. The insulin response occurred earlier than that induced by either glucose or tolbutamide. None of the usual modifiers of insulin secretion significantly altered this secretory response. Glycolytic inhibitors, adrenergic agonists and blocking agents, cholinergic blocking agents, mitotic spindle inhibitors, and agents influencing sodium pump activity failed to alter hyposmolar-induced insulin secretion. Manipulation of the perifusion medium calcium concentration was the only procedure tested that influenced the secretory response. Perturbations of medium calcium concentration that increased the tissue-to-medium calcium gradient augmented the hyposmolar-induced insulin response and those that decreased tissue-to-medium calcium gradient greatly inhibited the response. The precise cause of the insulin response to a decrease in bathing fluid osmolarity remains undefined; however, the stimulus is not specific for insulin because increases in glucagon and amylase were also elicited by the hyposmolar stimulus.

Differential effects of microtubule-altering agents on beta-cells during development

1983 ◽  
Vol 245 (4) ◽  
pp. E391-E400
Author(s):  
R. S. Hill ◽  
W. B. Rhoten
Keyword(s):  
Insulin Secretion ◽  
Beta Cells ◽  
Insulin Release ◽  
High Glucose ◽  
Deuterium Oxide ◽  
Inhibitory Effect ◽  
Secretory Response ◽  
Second Phase ◽  
Insulin Secretory Response

The effect of microtubule-altering agents on the insulin secretory response to glucose during the perinatal period was investigated with an in vitro perifusion system. Rat pancreatic mince from day 17 of gestation (D17G) to day 6 postnatally (D6PN) were perifused for 60 min in basal glucose followed by 45 min with high glucose (3.5 mg/ml) or with high glucose plus 10 mM arginine (D17G). The two phases of insulin secretion in response to high glucose developed in an age-dependent and asynchronous manner. The first phase matured between D17G and D18G, and maturation of the second phase occurred subsequently. Vinblastine (VB) (20 or 100 microM) had a differential effect on the insulin secretory response. VB did not inhibit stimulated insulin release at D17G. This absence of an inhibitory effect of VB at D17G could not be explained by the absence of polymerized tubulin because microtubules were present in the control beta-cells and, in addition, VB treatment resulted in the formation of paracrystalline deposits. Subsequently in development, and with isolated islets of the adult, VB inhibited stimulated insulin release. Heavy water (deuterium oxide, D2O) inhibited stimulated insulin secretion at D17G but blocked completely insulin release from the near-term beta-cell. The inhibition of insulin secretion by D2O was rapidly reversed when water replaced D2O in the perifusion media. The results indicate that the maturation of the second phase of insulin secretion coincides with the ability of the microtubule-altering agents to modify the insulin secretory response. One possible explanation for these findings is that at D17G the microtubules are not coupled physicochemically to other molecules or structures necessary for their role in insulin secretion to be expressed fully.

Inhibition by rat diazepam-binding inhibitor/acyl-CoA-binding protein of glucose-induced insulin secretion in the rat

1994 ◽  
Vol 131 (2) ◽  
pp. 201-204 ◽  
Author(s):  
Claes-Göran Östenson ◽  
Bo Ahrén ◽  
Sven Karlsson ◽  
Jens Knudsen ◽  
Suad Efendic
Keyword(s):  
Insulin Secretion ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Binding Protein ◽  
Insulin Response ◽  
Isolated Islets ◽  
High Concentration ◽  
Isolated Pancreatic Islets ◽  
Rat Pancreas

Östenson C-G, Ahrén B, Karlsson S, Knudsen J, Efendic S. Inhibition by rat diazepam-binding inhibitor/ acyl-CoA-binding protein of glucose-induced insulin secretion in the rat. Eur J Endocrinol 1994;131:201–4. ISSN 0804–4643 Diazepam-binding inhibitor (DBI) has been localized immunohistochemically in many organs. In porcine and rat pancreas, DBI is present in non-B-cells of the pancreatic islets. Porcine peptide also has been shown to suppress insulin secretion from rat pancreas in vitro. Recently, acyl-CoA-binding protein (ACBP) was isolated from rat liver and shown to be identical structurally to DBI isolated from rat brain. Using this rat DBI/ACBP, we have studied its effects on glucose-stimulated insulin secretion in the rat, both in vivo and in isolated pancreatic islets. Infusion iv of rDBI/ACBP (25 pmol/min) during glucose stimulation induced a moderate and transient reduction of plasma insulin levels. Moreover, rDBI/ACBP suppressed insulin release from batch-incubated isolated islets, stimulated by 16.7 mmol/l glucose, by 24% at 10 nmol/l (p < 0.05) and by 40% at 100 nmol/l (p < 0.01). The peptide (100 nmol/l) also inhibited the insulin response to glucose (16.7 mmol/l) from perifused rat islets by 31% (p < 0.05), mainly by affecting the acute-phase response. Finally, incubation of isolated islets in the presence of rDBI/ACBP antiserum (diluted 1:100 and 1:300) augmented the insulin response to 16.7 mmol/l glucose (p < 0.05 or even less). We conclude that rDBI/ACBP, administered iv or added to the incubation media, suppresses insulin secretion in the rat but that the effect is moderate despite the high concentration used. It is therefore unlikely that the peptide modulates islet hormone release, acting as a classical hormone via the circulation. However, the occurrence of DBI/ACBP in the islets and the enhancing effect by the rDBI/ACBP antibodies on glucose-stimulated insulin release suggest that the peptide is a local modulator of insulin secretion. C-G Östenson, Department of Endocrinology, Karolinska Hospital, S-171 76 Stockholm, Sweden

Insulin secretory response to different secretagogues in hyper- and hypothyroid mice

1981 ◽  
Vol 97 (4) ◽  
pp. 508-513 ◽  
Author(s):  
Bo Ahrén ◽  
Ingmar Lundquist
Keyword(s):  
Glucose Level ◽  
Plasma Glucose ◽  
Muscle Glycogen ◽  
Insulin Response ◽  
Liver Glycogen ◽  
Secretory Response ◽  
Thyroid State ◽  
Lower Glucose ◽  
Insulin Secretory Response

Abstract. The influence of long-term changes in thyroid state on insulin secretion was investigated in vivo in mice. Hyperthyroidism was induced by daily injections of i.-triiodothyronine and hypothyroidism by a single injection of 131I. Four different insulin secretagogues were used to characterize the insulin secretory response, i.e. glucose, the β2-adrenoceptor agonist terbutaline, the cholinergic agonist carbachol and the synthetic C-terminal octapeptide of cholecystokinin, CCK-8. In the hyperthyroid mice the plasma glucose level was moderately decreased. Despite this lower glucose level the insulin response to terbutaline and glucose were potentiated by about 200%. Insulin response to CCK-8 and carbachol was less enhanced, by about 100 and 50%, respectively. Liver and muscle glycogen levels were markedly reduced. The hypothyroid animals showed reduced insulin responses to all secretagogues; after terbutaline by 100%, after carbachol by 70%, after glucose and CCK-8 by 50%. Plasma glucose and muscle glycogen levels were normal, whereas liver glycogen levels were moderately enchanced. Insulin release induced by β-adrenoceptor stimulation was most markedly affected by the thyroid state, which thus may be of importance for the balance between the β- and α-adrenoceptors of the insulin cell. Since thyroid activity influenced the insulin response to all secretagogues it cannot be excluded that the thyroid state also exerts effects not related to the adrenoceptors.

In vivo endotoxin and IL-1 potentiate insulin secretion in pancreatic islets

1990 ◽  
Vol 258 (4) ◽  
pp. R1070-R1077 ◽  
Author(s):  
M. R. Yelich
Keyword(s):  
Insulin Secretion ◽  
Pancreatic Islets ◽  
Interleukin 1 ◽  
Similar Extent ◽  
Isolated Pancreatic Islets ◽  
In Vitro Insulin Secretion ◽  
In Vivo Effects ◽  
Insulin Secretory Response

This study evaluated the in vivo effects of endotoxin and interleukin 1 (IL-1) on in vitro insulin secretion from perfused rat pancreases and isolated pancreatic islets. Glucose-induced insulin secretion was potentiated in pancreases obtained from rats 3 h after endotoxin or 30 min after IL-1. Studies using isolated pancreatic islets indicated that islet sensitivity to glucose was increased by either endotoxin or IL-1 to a similar extent, but there was no effect of endotoxin or IL-1 on the maximal insulin secretory response of islets to glucose. Insulin secretion was not potentiated in perfused pancreases obtained from rats only 30 min after treatment with endotoxin. These results suggest that in vivo treatment with either endotoxin or IL-1 potentiates insulin secretion by increasing islet sensitivity to glucose. In addition, because endotoxin is known to potently stimulate the production and secretion of IL-1 in vivo, the results lend support to the hypothesis that the effects of endotoxin on insulin secretion may be mediated partially by IL-1.

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