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.

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.

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

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.

In vitro fertilization in inbred BALB/c mice I: isotonic osmolarity and increased calcium-enhanced sperm penetration through the zona pellucida and male pronuclear formation

Zygote ◽  
2008 ◽  
Vol 16 (3) ◽  
pp. 249-257 ◽  
Author(s):  
Seiji Kito ◽  
Yuki Ohta
Keyword(s):  
Calcium Concentration ◽  
Detrimental Effect ◽  
Choline Chloride ◽  
Positive Control ◽  
Basic Medium ◽  
Vitro Fertilization ◽  
Medium Osmolarity ◽  
Sperm Penetration ◽  
Pronuclear Formation

SummaryTo optimize IVF conditions for BALB/c mice, which are known to have poor in vitro fertilizability, the requirements for sperm–ova interaction were studied by use of modified simplex optimization medium (mKSOM) as a basic medium. Modified human tubal fluid (mHTF) was used for sperm preincubation and acted as a positive control. When the two media were compared, neither capacitation nor fertilization was supported in mKSOM. Increasing the calcium concentration in mKSOM to 5 mM or more during sperm: ova coincubation improved zona penetration but not male pronuclear (MPN) formation to the same level as those cells incubated in mHTF. When medium osmolarity was varied from 230–305 mOsmol by NaCl at 5 mM CaCl2, MPN formation improved at 280 mOsmol or higher osmolarity to the same level as that found when using mHTF. When NaCl equivalent to 25–75 mOsmol was substituted with trehalose, no significant reduction in fertilization was observed. Substitution of NaCl equivalent to 75 mOsmol with other osmotic reagents (sucrose, choline chloride and sorbitol) resulted in similar levels of fertilization as found with mHTF, except for sorbitol, which reduced fertilization significantly caused by its detrimental effect on sperm viability. At isotonic osmolarity (305 mOsmol), maximum fertilization was observed at 5 mM CaCl2; lower or higher concentrations of CaCl2 resulted in reduced fertilization. Calcium and osmolarity, therefore, are important for sperm : ova interaction in BALB/c mice and the increases in calcium to 5 mM and osmolarity to 305 mOsmol are optimal for BALB/c sperm to penetrate through the zona and to form MPN.

Magnesium requirement for somatostatin inhibition of insulin secretion

1984 ◽  
Vol 105 (1) ◽  
pp. 83-86 ◽  
Author(s):  
Donald L. Curry ◽  
Leslie L. Bennett
Keyword(s):  
Insulin Secretion ◽  
Calcium Concentration ◽  
Inhibitory Effect ◽  
Secretory Process ◽  
Magnesium Ion ◽  
Second Phase ◽  
Intracellular Membrane ◽  
Calcium Magnesium ◽  
First Phase Insulin Secretion ◽  
Insulin Secretory Response

Abstract. Rat pancreas perfusions were performed using a perfusate with a fixed calcium concentration of 5 mEq/l and magnesium varying from 0 to 0.6 mEq/dl. Insulin secretion was stimulated by a constant glucose infusion of 300 mg/dl. This glucose concentration produces the typical biphasic insulin secretory response. We observed that in the absence of magnesium, somatostatin concentrations of 0.5 and 2.0 ng/ml were without effect on first phase insulin secretion. However, these same somatostatin levels produced 50% or more inhibition of insulin secretion in the presence of magnesium at 0.3 or 0.6 mEq/l. Similarly, in the absence of magnesium, somatostatin at 50 ng/ml failed to inhibit second phase insulin secretion, whereas this same somatostatin level produced about 50% inhibition of insulin secretion in the presence of magnesium at 0.3 mEq/l. Thus, altering perfusate magnesium concentrations without changing calcium is an important determinant of the degree of inhibition of secretion produced by somatostatin. In particular, in the absence of magnesium ion, somatostatin concentrations which would 'normally' produce 50% inhibition of secretion (ID50) are without effect. Therefore, magnesium ion is necessary for the full inhibitory effect of somatostatin to occur. These results suggest that inhibitors, as well as potentiators, of the insulin secretory process may act by altering intracellular/membrane calcium-magnesium ratios, but in opposite directions.

scholarly journals Disruption of the Dopamine D2 Receptor Impairs Insulin Secretion and Causes Glucose Intolerance

Endocrinology ◽  
2010 ◽  
Vol 151 (4) ◽  
pp. 1441-1450 ◽  
Author(s):  
Isabel García-Tornadú ◽  
Ana M. Ornstein ◽  
Astrid Chamson-Reig ◽  
Michael B. Wheeler ◽  
David J. Hill ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glucose Intolerance ◽  
Dopamine D2 Receptor ◽  
D2 Receptor ◽  
Insulin Response ◽  
Wild Type ◽  
Β Cell ◽  
Insulin Response To Glucose

The relationship between antidopaminergic drugs and glucose has not been extensively studied, even though chronic neuroleptic treatment causes hyperinsulinemia in normal subjects or is associated with diabetes in psychiatric patients. We sought to evaluate dopamine D2 receptor (D2R) participation in pancreatic function. Glucose homeostasis was studied in D2R knockout mice (Drd2−/−) mice and in isolated islets from wild-type and Drd2−/− mice, using different pharmacological tools. Pancreas immunohistochemistry was performed. Drd2−/− male mice exhibited an impairment of insulin response to glucose and high fasting glucose levels and were glucose intolerant. Glucose intolerance resulted from a blunted insulin secretory response, rather than insulin resistance, as shown by glucose-stimulated insulin secretion tests (GSIS) in vivo and in vitro and by a conserved insulin tolerance test in vivo. On the other hand, short-term treatment with cabergoline, a dopamine agonist, resulted in glucose intolerance and decreased insulin response to glucose in wild-type but not in Drd2−/− mice; this effect was partially prevented by haloperidol, a D2R antagonist. In vitro results indicated that GSIS was impaired in islets from Drd2−/− mice and that only in wild-type islets did dopamine inhibit GSIS, an effect that was blocked by a D2R but not a D1R antagonist. Finally, immunohistochemistry showed a diminished pancreatic β-cell mass in Drd2−/− mice and decreased β-cell replication in 2-month-old Drd2−/− mice. Pancreatic D2Rs inhibit glucose-stimulated insulin release. Lack of dopaminergic inhibition throughout development may exert a gradual deteriorating effect on insulin homeostasis, so that eventually glucose intolerance develops.

Extracellular calcium and adrenergic and cholinergic effects on islet beta-cell function

1976 ◽  
Vol 231 (4) ◽  
pp. 1246-1249 ◽  
Author(s):  
IM Burr ◽  
AE Slonim ◽  
V Burke ◽  
T Fletcher
Keyword(s):  
Insulin Release ◽  
Calcium Concentration ◽  
Direct Evidence ◽  
Cell Function ◽  
Insulin Response ◽  
Calcium Content ◽  
Biphasic Insulin Release ◽  
Perifusion System ◽  
Cholinergic Effects

An in vitro perifusion system utilizing collagen-medium calcium on the dynamics of insulin release as induced by acetylcholine (ACh) stimulation (in the presence of glucose, 2.4 mM) and as modified by prior perfusion of islets in epinephrine. Continuous challenge with ACh produces a biphasic insulin release response, both phases of which are reduced when the medium calcium concentration is reduced during stimulation; when the calcium content is reduced during an initial perifusion period of 30 min and then replaced during subsequent stimulation only the first phase of the response to ACh is affected; perifusion with epinephrine prior to stimulation with ACh produces enhancement of both phases of ACh-induced insulin release when calcium in both media is normal. However,.when this experiment is repeated utilizing a medium with low calcium content during the period of exposure to epinephrine the priming effect of epinephrine on the subsequent insulin response to ACh is abolished (in fact, reversed). These studies provide direct evidence for a role for calcium in mediating an effect of epinephrine on insulin release. Further, the data suggest that epinephrine affects Ca transport in islets in some manner beyond stimulating net efflux from islets, perhaps by enhancing membrane binding of calcium.

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 Loss-of-Function Mutation of the Galanin Gene Is Associated with Perturbed Islet Function in Mice

Endocrinology ◽  
2004 ◽  
Vol 145 (7) ◽  
pp. 3190-3196 ◽  
Author(s):  
Bo Ahrén ◽  
Giovanni Pacini ◽  
David Wynick ◽  
Nils Wierup ◽  
Frank Sundler
Keyword(s):  
Insulin Secretion ◽  
Islet Cells ◽  
Insulin Response ◽  
Tolerance Test ◽  
Glucose Disposal ◽  
Islet Function ◽  
Loss Of Function ◽  
Euglycemic Hyperinsulinemic Clamp

Abstract The neuropeptide galanin is expressed in sympathetic nerve terminals that surround islet cells and inhibits insulin secretion. To explore its role for islet function, we studied mice with a loss-of-function mutation in the galanin gene [galanin knockout (KO) mice]. Intravenous 2-deoxy-glucose, which activates both the sympathetic and parasympathetic branches of the autonomic nervous system, caused an initial (1–5 min) inhibition of insulin secretion that was impaired in galanin KO mice (P = 0.027), followed by a subsequent stimulation of insulin secretion that was augmented in galanin KO mice (P &lt; 0.01). Similar effects were seen after chemical sympathectomy by 6-hydroxydopamine. In contrast, galanin KO mice had a reduced insulin response to glucose, both in vivo (P &lt; 0.001) and in isolated islets (P &lt; 0.001), and to arginine, both in vivo (P = 0.012) and in vitro (P = 0.018). During an iv glucose tolerance test, galanin KO mice had impaired glucose disposal (P = 0.005) due to a reduced insulin response (P &lt; 0.001) and a reduced insulin-independent glucose elimination (glucose effectiveness; P = 0.040). Insulin sensitivity, as judged by a euglycemic, hyperinsulinemic clamp technique, was slightly increased in galanin KO mice (P = 0.032). We conclude that 1) galanin may contribute to sympathetic influences inhibiting insulin secretion in mice, and 2) galanin KO mice have a reduced glucose-induced insulin secretion.

REGULATION OF INSULIN SECRETION IN THE OVINE FOETUS IN UTERO. EFFECTS OF SODIUM VALERATE ON SECRETION AND OF ADRENOCORTICOTROPHIN-INDUCED PREMATURE PARTURITION ON THE INSULIN SECRETORY RESPONSE TO GLUCOSE

1973 ◽  
Vol 56 (1) ◽  
pp. 13-25 ◽  
Author(s):  
J. M. BASSETT ◽  
G. D. THORBURN ◽  
DIANNE H. NICOL
Keyword(s):  
Insulin Secretion ◽  
Plasma Insulin ◽  
Short Chain Fatty Acid ◽  
Plasma Concentrations ◽  
Insulin Level ◽  
In Utero ◽  
Secretory Response ◽  
Lower Plasma ◽  
Insulin Secretory Response ◽  
Corticosteroid Secretion

SUMMARY Intravenous infusions of glucose into lambs in utero (130–150 days) and after birth, confirmed the marked post-natal increase in the magnitude of the response of plasma insulin to glucose. These studies also suggest that insulin secretion in foetal lambs is stimulated by glucose at lower plasma concentrations than in lambs after birth. The short-chain fatty acid, valeric acid, given as the sodium salt, caused a very rapid increase in the plasma insulin level of foetal lambs, when given either by intravenous injection or infusion. When birth was induced after only 135 days of gestation by i.v. infusion of a synthetic adrenocorticotrophin preparation (Synacthen) into foetal lambs there was also a prematurely induced maturation of the insulin secretory response to glucose. In these prematurely born lambs the insulin secretory response to i.v. glucose infusion was similar to that of normal lambs after birth and differed greatly from that of normal foetuses of similar age. The results indicate that maturation of the insulin secretory mechanism in the lamb is associated with parturition and suggest that these changes may be consequences of the increasing corticosteroid secretion in the foetus during the last few days of gestation.

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