Dynamics Of Insulin Secretion Research Articles

Metformin administration was associated with a modification of LH, prolactin and insulin secretion dynamics in women with polycystic ovarian syndrome

Aim. To elucidate the dynamics of FSH, LH, prolactin (PRL), TSH and insulin secretion in women with polycystic ovarian syndrome (PCOS) treated with metformin (MET).Patients and methods. In a prospective, controlled and randomised trial, 32 women with PCOS and 32 with normal cycle were recruited to receive MET (850 mg b.i.d.) or placebo (n: 16 for each subgroup) for an average of 40 days. Pituitary function and insulin secretion were assessed before and after intervention by GnRH-TRH tests and oral glucose tolerance test induced insulin response.Results. Basal and area under the response curve (AURC) LH values were higher in PCOS than in normal controls before MET and declined following treatment in the former group (P < 0.05). Ovulatory PCOS responders had lower basal LH, AURCLH and AURCPRL values during MET than anovulatory cases (P < 0.05 for all) and AURCins was lower in ovulatory than anovulatory PCOS before and on MET (P < 0.02–P < 0.05), with a rise of QUICKY index in the former group during MET treatment (P < 0.05). FSH and TSH were similar.Conclusions. MET administration lowered LH activity in all PCOS women and in ovulatory responders and also compromised PRL stimulated secretion in the latter cases. These findings were indicative of an effect of MET on pituitary activity.

The role of leptin, soluble leptin receptor, resistin, and insulin secretory dynamics in the pathogenesis of hypothalamic obesity in children

In this study, we have investigated the role of leptin, soluble leptin receptor(sOb-R), resistin, and insulin secretory dynamics in the development of hypothalamic obesity. Children who had hypothalamo-pituitary tumor were divided into two groups. First group included obese-overweight (hypothalamic obese = HOB group, n = 23) and second group included non-obese children (hypothalamic non-obese = HNOB group, n = 16). Exogenously obese-overweight children (OB group, n = 22) were included as controls. Basal and second-hour serum glucose and insulin in oral glucose tolerance test (OGTT), basal serum leptin, sOb-R, resistin levels, and homeostasis model assessment (HOMA) indexes were compared between the groups. Age, sex, and pubertal status were similar in study groups. Median and interquartile ranges of body mass index (BMI) z scores were similar in HOB and OB groups (2.0 (1.5-2.1) and 2.1 (1.8-2.3), respectively). Serum leptin levels corrected for BMI were highest and total leptin/sOb-R ratios (free leptin index (FLI)) tended to be higher in HOB than HNOB and OB groups, indicating leptin resistance (leptin/BMI, 4.0 (1.6-5.2), 1.5 (0.8-3.1), and 2.5 (1.8-3.5); FLI, 2.0 (0.8-3.5), 0.6 (0.3-1.2), and 1.5 (1-2.3) in HOB, HNOB, and OB groups; respectively). Serum resistin levels were similar in groups (2.6 (1.9-3.1), 2.8 (1.7-3.4), and 3.0 (2.2-3.5) ng/ml in HOB, HNOB, and OB groups, respectively). Basal serum glucose, basal and second-hour insulin levels in OGTT, and HOMA index were higher in OB group than the HOB and HNOB groups, indicating insulin resistance in simple obesity; however, increment of insulin to same glycemic load in OGTT was highest in the HOB group indicating insulin dysregulation (p < 0.05). Hypothalamic obesity seems to be related to both dysregulated afferent (leptin) and efferent (insulin) neural outputs through the autonomic nervous system resulting in energy storage as fat.

Significance of acanthosis nigricans in childhood obesity

Acanthosis nigricans (AN) is among the most common dermatologic manifestations of obesity and hyperinsulinism. In this study, we aimed to find the clinical and laboratory differences in obese children with AN and without AN (non-AN). In total, 160 obese children were included in the study. The duration of obesity, body mass index (BMI), BMI z-scores, birth weight, parental BMI, lipid profile, fasting and post-meal (PM) glucose and insulin levels were compared in 67 obese with AN and 93 obese without AN. Age was similar in both groups. AN group had higher male to female ratio (42/25 in AN, 43/50 in non-AN; P = 0.03), higher BMI (30.3 +/- 6.1 in AN, 26.4 +/- 3.6 in non-AN; P < 0.001) and weight for height (162.6 +/- 28.8 in AN, 144.6 +/- 15.8 in non-AN; P < 0.001) than non-AN group. There were no significant differences between the groups in birth weight, parental BMI and blood pressure. AN group had higher fasting (19.9 +/- 16.2 mU/L in AN, 10.4 +/- 7.6 mU/L in non-AN; P < 0.001) and PM insulin (88.6 +/- 87.3 mU/L in AN, 51.1 +/- 42.0 mU/L in non-AN; P = 0.01) and homeostasis model assessment for insulin resistance (HOMA-IR) (4.0 +/- 2.5 in AN, 2.2 +/- 1.8 in non-AN; P < 0.001) than non-AN group. However, fasting and PM glucose, triglyceride, low-density lipoprotein-, high-density lipoprotein- and total cholesterol levels were similar in both groups. BMI was correlated with HOMA-IR in both groups (r = 0.40 for AN, r = 0.28 for non-AN). PM glucose and PM insulin were correlated in both groups (r = 0.56 for AN, r = 0.39 for non-AN). However, fasting glucose and fasting insulin were correlated in only non-AN (r = 0.25), but not in AN group. Obese children with AN show higher insulin levels and HOMA-IR. AN is an important predictor of the insulin resistance in childhood obesity. Insulin secretory dynamics seem to be disrupted in fasting state initially, which is reflected as the loss of fasting insulin-glucose correlation in AN group.

Nutrient control of insulin secretion in perifused adult pig islets

Objectives Xenotransplantation of pig islets is a potential solution to the shortage of human islets, but our knowledge of how these islets secrete insulin in response to nutrients is still fragmentary. This was the question addressed in the present study. Methods After 24 h culture adult pig islets were perifused to characterize the dynamics of insulin secretion. Some responses were compared to those in human islets. Results Increasing glucose from 1 to 15 mM weakly (~ 2×) stimulated insulin secretion, which was potentiated (~ 12×) by the cAMP-producing agent, forskolin. The effect of glucose was concentration-dependent (threshold at 3 –5 mM and maximum at ~ 10 mM). The pattern of secretion was biphasic with a small first phase and an ascending second phase, and a paradoxical increase when the glucose concentration was abruptly lowered. Diazoxide abolished glucose-induced insulin secretion and tolbutamide reversed the inhibition. Glucose also increased secretion when islets were depolarized with tolbutamide or KCl. Insulin secretion was increased by leucine + glutamine, arginine, alanine or a mixture of amino acids, but their effect was significant only in the presence of forskolin. Upon stimulation by glucose alone, human islets secreted ~10× more insulin than pig islets, and the kinetics was characterized by a large first phase, a flat second phase, and rapid reversibility. Conclusions Compared with human islets, in vitro insulin secretion by adult pig islets is characterized by a different kinetics and a major quantitative deficiency that can be corrected by cAMP.

Insulin secretion dynamics of free and alginate-encapsulated insulinoma cells

This study investigates the effect of alginate/poly-L: -lysine/alginate (APA) encapsulation on the insulin secretion dynamics exhibited by an encapsulated cell system. Experiments were performed with the aid of a home-built perfusion apparatus providing a 1 min temporal resolution. Insulin profiles were measured from: (i) murine insulinoma betaTC3 cells encapsulated in calcium alginate/poly-L: -lysine/alginate (APA) beads generated with high guluronic (G) or high mannuoric (M) content alginate, and (ii) murine insulinoma betaTC-tet cells encapsulated in high M APA beads and propagated in the presence and absence of tetracycline. Results show that encapsulation in APA beads did not affect the insulin secretion profile shortly post-encapsulation. However, remodeling of the beads due to cell proliferation affected the insulin secretion profiles; and inhibiting remodeling by suppressing cell growth preserved the secretion profile. The implications of these findings regarding the in vivo function of encapsulated insulin secreting cells are discussed.

Munc13-1 is required for the sustained release of insulin from pancreatic β cells

Munc13-1 is a presynaptic protein that is essential for synaptic vesicle priming. Deletion of Munc13-1/unc13 causes total arrest of synaptic transmission due to a complete loss of fusion-competent synaptic vesicles. The requirement of Munc13-1 for large dense-core vesicles (LDCVs), however, has not been established. In the present study, we use Munc13-1 knockout (KO) and diacylglycerol (DAG) binding-deficient Munc13-1(H567K) mutant knockin (KI) mice to determine the role of Munc13-1 in the secretion of insulin-containing LDCVs from primary cultured pancreatic beta cells. We show that Munc13-1 is required for the sustained insulin release upon prolonged stimulation. The sustained release involves signaling of DAG second messenger, since it is also reduced in KI mice. Insulin secretion in response to glucose stimulation is characterized by a biphasic time course. Our data show that Munc13-1 plays an essential role in the development of the second phase of insulin secretion by priming insulin-containing LDCVs.

Use of glucose‐responsive material to regulate insulin release from constitutively secreting cells

Genetically-engineered cells offer a solution to the cell availability problem in tissue engineering a pancreatic substitute for the treatment of insulin-dependent diabetes. These cells can be non-beta cells, such as hepatocytes or myoblasts, retrieved as a biopsy from the same patient and genetically engineered to secrete recombinant insulin constitutively or under transcriptional regulation. However, the continuous or slowly responsive insulin secretion dynamics from these cells cannot provide physiologic glucose regulation in patients. Our objective consists of using such cells as an insulin source and of regulating insulin release by incorporating a glucose-responsive material, which acts as a control barrier for insulin in a cell-material hybrid device. Experiments were performed with insulinoma betaTC3 cells, HepG2 hepatomas, and C2C12 myoblasts, the latter two genetically-modified to constitutively secrete insulin. The control barrier consisted of concanavalin A (con A)-based glucose-responsive material, which forms a gel at low and a sol at high glucose concentrations. Results demonstrated that the device released insulin at a higher rate in response to glucose challenges. In contrast, a device containing an inert hydrogel instead of glucose-responsive material released insulin at an essentially constant rate, irrespective of the surrounding glucose concentration. Necessary material improvements include increased sensitivity to glucose, so that the material responds to physiologically relevant glucose concentrations, and increased stability. The prospects of developing a properly functional, implantable substitute based on engineered non-beta cells and glucose-responsive material, and the material and device improvements that need to be made prior to in vivo experiments, are discussed.

2型糖尿病におけるナテグリニド適応症例についての検討

Nateglinide is a novel rapid- and short-acting insulin secretagogue that ameliorates postprandial hyperglycemia by improving insulin secretory dynamics to a near normal level more effectively than sulfonylureas. Recent epidemiological studies have demonstrated that postprandial hyperglycemia can result in arteriosclerosis, and that advanced arteriosclerosis is present in the initial stage of impaired glucose tolerance. Since postprandial hyperglycemia could be well treated by nateglinide, we examined the background factors of type 2 diabetic patients to determine the optimal indication for nateglinide. Our results indicate that nateglinide is most effective in young and obese patients. Furthermore, fewer responders had microangiopathy or were previously on oral hypoglycemic agents or sulfonylureas compared with non-responders. Although nateglinide is generally indicated for patients with mild HbA1c level, the present findings indicate that the drug was effective in the aforementioned patients regardless of pretreatment HbA1c levels. In one obese patient, nateglinide improved late hyperinsulinemia to near normal secretory dynamics. Our findings suggest that nateglinide is a physiologically preferable and useful drug for early type 2 diabetes without microangiopathy.

Regulation of Insulin Secretion in Islets of Langerhans by Ca2+Channels

Insulin secretion from beta-cells of the pancreatic islets of Langerhans is triggered by Ca(2+) influx through voltage-dependent Ca(2+) channels. Electrophysiological and molecular studies indicate that beta-cells express several subtypes of these channels. This review discusses their roles in regulating insulin secretion, focusing on recent studies using beta-cells, exogenous expression systems, and Ca(2+) channel knockout mice. These investigations reveal that L-type Ca(2+) channels in the beta-cell physically interact with the secretory apparatus by binding to synaptic proteins on the plasma membrane and insulin granule. As a result, Ca(2+) influx through L-type channels efficiently and rapidly stimulates release of a pool of insulin granules in close contact with the channels. Thus, L-type Ca(2+) channel activity is preferentially coupled to exocytosis in the beta-cell, and plays a critical role in regulating the dynamics of insulin secretion. Non-L-type channels carry a significant portion of the total voltage-dependent Ca(2+) current in beta-cells and cell lines from some species, but nevertheless account for only a small fraction of insulin secretion. These channels may regulate exocytosis indirectly by affecting membrane potential or second messenger signaling pathways. Finally, voltage-independent Ca(2+) entry pathways and their potential roles in beta-cell function are discussed. The emerging picture is that Ca(2+) channels regulate insulin secretion at multiple sites in the stimulus-secretion coupling pathway, with the specific role of each channel determined by its biophysical and structural properties.

Acute pancreatitis, expression of inducible nitric oxide synthase and defective insulin secretion.

A high level of nitric oxide (NO) produced by inducible NO synthase (iNOS) is involved in pancreatic beta-cell dysfunction and apoptosis. In the present study, we examined whether iNOS is also expressed in beta cells after induction of acute pancreatitis (AP) in the rat. Pancreatic islets taken from AP animals and incubated for 60 min in the presence of 20.0 mmol/l glucose showed a decreased insulin secretory response to glucose. The basal insulin release at 1.0 mmol/l glucose was also moderately reduced. Experiments on the dynamics of insulin secretion from perfused pancreas revealed an impairment of both first and second phase of glucose-stimulated insulin release after the induction of AP. Confocal microscopy demonstrated that most of the beta cells in pancreas of rat with AP expressed strong immunoreactivity for iNOS. This was further confirmed by biochemical and Western blot analysis that showed a marked increase in iNOS protein expression and enzyme activity concomitant with a modest reduction in the cNOS protein and activity. Although the mechanisms underlying the defective insulin secretory response of beta cells seen during the early stage of AP are complex, the present finding suggests that the expression of iNOS and a marked iNOS-derived NO production in the beta cells may play at least a contributory role in the impairment of beta-cell function.

Anion-selective amplification of glucose-induced insulin secretion.

The functional roles of anions on glucose-induced insulin secretion are poorly understood. We investigated the effects of the monovalent anions thiocyanate, iodide, bromide, nitrate and chloride on the dynamics of insulin secretion in isolated pancreatic islets from non-inbred Umeå ob/ob mice. All anion species (12 mM), except Cl-, significantly amplified glucose-induced (20 mM) first- and second-phase insulin secretion (selectivity sequence: SCN->NO3->I->Br->Cl-). Simultaneously, the anions reduced the lag-time prior to the initiation of the secretion (SCN-=I-=NO3->Br->Cl-). The results indicate that pancreatic beta-cell activation can be initiated and amplified by an anion-selective mechanism showing increasing degrees of activation in the order of the anion series of Hofmeister. On the basis of the strikingly similar anion selectivity of amplified secretion and shortened lag-phase, we suggest that both types of anion effects are caused by action at a single site on the beta-cell.

ISLETS IN ALGINATE MACROBEADS REVERSE DIABETES DESPITE MINIMAL ACUTE INSULIN SECRETORY RESPONSES1

Encapsulation of islets has been widely investigated as a treatment for diabetes. The characteristics and dynamics of insulin secretion by encapsulated islets in response to glucose and other secretagogues are not well understood. In our study, macroencapsulated syngeneic islets at 3-4 wk after transplantation were studied for insulin release in response to i.v. glucose (hyperglycemic clamps at 250 or 350 mg/dl plasma glucose), arginine (i.v. bolus, 100 mg/kg), glucagon-like peptide-1 (i.v. infusion for 20 min, 2.2 pmol/kg/min), and meal challenge. Syngeneic islets (6000 islets) were encapsulated in alginate macrobeads (2-3 mm diameter) with or without poly-L-lysine coating and transplanted into the peritoneal cavity of STZ-diabetic Lewis rats. Normal (nontransplanted) and diabetic Lewis rats transplanted with "naked" islets under the kidney capsule served as controls. Animals transplanted with macrobeads displayed subnormal insulin responses to glucose, arginine, and glucagon-like peptide-1 despite achieving normoglycemia faster than animals with renal subcapsular islet transplants. Plasma insulin responses to meal challenges were blunted in animals with macrobeads resulting in increased plasma glucose excursions. We conclude that, after transplantation into diabetic Lewis rats, macroencapsulated islets have significantly impaired insulin secretion despite achieving normal fed glycemic levels.

Dynamics of insulin secretion in obesity and diabetes.

Insulin resistance and compensatory hyperinsulinemia are commonly present in obesity. The biochemical mechanisms responsible for the maintenance of basal hypersecretion of insulin are reviewed in this article. Under basal, fasting and fed conditions the hyperinsulinemia of obesity largely depends on increased insulin secretion, without any alteration of the temporal secretion. This suggests that the functioning beta cell mass is enhanced, but normal regulatory mechanisms are maintained. A number of alterations in beta-cell function are present in conditions of impaired glucose tolerance which precede the onset of overt diabetes.

Dynamic changes in plasma proinsulin/insulin ratio during insulin secretion influence correlation between radioimmunoassay (RIA) and IMX measurements of insulin

Because proinsulin and insulin have different circulatory half-lives, the ratio of proinsulin to insulin in plasma depends on the dynamics of insulin secretion. This variation can potentially influence comparison of IMX assays and radioimmunoassays (RIAs) for [insulin], given that the antibody used in the IMX assay has negligible cross-reactivity with proinsulin compared to the 40% cross-reactivity with proinsulin of the antibody used in the RIA. Simulation of a simple mass balance model for insulin and proinsulin concentrations during an oral glucose tolerance test predicts that the ratio ( R) of RIA to IMX insulin measurements of [insulin] should transiently decrease, pass through a minimum, increase past the initial value, pass through a maximum and eventually return to the initial value. Using time course specimens from patients, this pattern of variation in R was observed in the majority (12/16) of cases studied. The variation in R for time course specimens (CV=26%) was significantly greater than for other specimens (fasting, random or undesignated; P<0.05). Thus, when comparing IMX and RIA measurements of [insulin], variation in R for samples from differing states of dynamic insulin secretion contains a component that is attributable to dynamic changes in the ratio of [proinsulin]/[insulin] in plasma.

Comparison of the effects of perchlorate and Bay K 8644 on the dynamics of cytoplasmic Ca2+ concentration and insulin secretion in mouse β-cells

Non-inbred ob/ob mice were used to study the dynamics of cytoplasmic Ca2+ concentration ([Ca2+]i) in isolated pancreatic beta-cells using microfluorimetry with fura 2/AM as probe, and the dynamics of insulin secretion in isolated pancreatic islets. D-Glucose (20 mM) caused a transient peak increase in [CA2+]i which changed to either an oscillating or a flat, elevated phase. The lag-time before the first peak increase in [Ca2+]i was markedly shortened by 12 mM ClO4- and the glucose-stimulated level of [Ca2+]i after the first peak was clearly elevated by the anion. ClO4- did not change the basal [Ca2+]i at 3 mM glucose. Extracellular Ca2+ deficiency abolished the effect of high glucose and ClO4- on [Ca2+]i. This suggests that ClO4- acts as an amplifier of transmembrane Ca2+ inflow. The L-type Ca2+ channel agonist, Bay K 8644 (0.01-1.0 microM), strictly reproduced all the effects of perchlorate on the glucose-stimulated beta-cell [Ca2+]i. Both phases of insulin release (20 mM glucose) were markedly enhanced by ClO4- (12 mM) or Bay K 8644 (1.0 microM). The lag-time for glucose-stimulated insulin release was shortened by both agents. Taken together, these data strengthen the idea that perchlorate amplifies the glucose-stimulation of [Ca2+]i and insulin release by directly modifying the function of the L-type Ca2+ channel. This effect can induce both a more prompt onset of and an amplified level of beta-cell secretory activity.

Reduced pancreatic insulin release and reduced peripheral insulin sensitivity contribute to hyperglycaemia in cystic fibrosis

Traditional opinion holds that patients with cystic fibrosis (CF) develop impaired glucose tolerance or diabetes due to insulinopenia caused by fibrosis of the pancreas. However, studies on the dynamics of insulin secretion and peripheral insulin action have yielded conflicting results. We studied 18 patients with CF (9 male, 9 female, age 15-29 years) and 17 healthy control subjects (8 male, 9 female, 20-32 years). Oral glucose tolerance tests and combined i.v.-glucose-tolbutamide-tests were performed on separate days in fasting subjects. Bergman's "Minimal Model" was used to quantitate both peripheral insulin sensitivity (SI) and insulin-independent glucose disposal (glucose effectiveness; SG). Based on National Diabetes Data Group criteria, 4 patients were classified as diabetic (22%; CF-DM), 3 patients (17%) had impaired glucose tolerance (CF-IGT) while glucose metabolism was normal in 11 patients (61%; CF-NGT). Irrespective of the degree of glucose tolerance, the insulin response to oral glucose was not reduced but delayed, up to 60 min in the CF-IGT/DM group. First-phase insulin release (0-10 min) after i.v.-glucose was significantly lower in CF patients (29% of healthy controls; P < 0.0001), with no difference between the CF-NGT and CF-IGT/DM groups. Insulin release following tolbutamide injection was only marginally reduced in CF patients (64% of controls). In contrast, SI was significantly reduced in the subgroup of CF patients with abnormal glucose metabolism (CF-IGT/DM: 0.97 +/- 0.16 x 10(-4) l/min/pmol; control group: 1.95 +/- 0.25; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Functional aspects of mouse islets transplanted to the kidney

To test whether the transplantation of pancreatic islets affects their basic functions, collagenase-isolated mouse islets were inserted under the left renal capsule of recipient animals. After various periods of time, grafts were removed from the kidney and examined for insulin content and secretory dynamics in a perifusion system. During syngeneic (C57BL/6, BALB/c) or subsyngeneic (NMRI) intrastrain transplantation, the graft insulin content fell drastically during the first week and stayed low for at least 6 weeks; first-phase secretion in general appeared suppressed. Immunosuppression by cyclosporin A had little effect on (sub)syngeneic grafts but markedly improved the performance of allotransplants. Daily injections of the calcium antagonist, verapamil, enhanced the insulin secretory responses of isolated grafts, whether (sub)syngeneic or allogeneic. In syngeneic and subsyngeneic grafts, the potentiating effect of acetylcholine on glucose-induced insulin release was markedly diminished, whereas that of caffeine was not. Transplanted islets also exhibited a subnormal responsiveness to the inhibiting action of noradrenaline. It is concluded that chronic denervation and transplantation of pancreatic islets may cause fundamental changes in the beta-cell responses to physiological regulators of insulin release.

The role of reduced glucose transporter content and glucose metabolism in the immature secretory responses of fetal rat pancreatic islets.

Isolated fetal islets show an immature or poor secretory response to nutrient secretagogues which may result from impaired mitochondrial oxidative processes. Insulin secretion, glucose metabolism and detection of metabolic enzymes by radiolabelling and immunoprecipitation were compared in islets isolated from neonatal (aged 5 days) and fetal rats (at 20 days gestation). The insulin secretory dynamics of fetal islets were abnormal in response to stimulation by glucose (10 mmol/l); a rapid release of insulin reaching a maximum 6 min after stimulation was observed with no rising second phase release. However, when the data were expressed as percentage of islet insulin content released, fetal islets released significantly more insulin than neonatal islets in response to glucose (4.86 +/- 0.45% vs 1.81 +/- 0.62%, p < 0.01) or 100 nmol/l glibenclamide (2.49 +/- 0.17% vs 0.25 +/- 0.06%, p < 0.001). Fetal islets however, failed to release insulin in response to stimulation by glyceraldehyde (10 mmol/l) unlike neonatal islets. Both glucose utilisation (as measured by the formation of [3H] H2O from 5-[3H] glucose) and glucose oxidation (as measured by the formation of [14C] CO2 from U-[14C] glucose) did not increase significantly in response to increasing the medium glucose concentration to 10 mmol/l whereas in neonatal islets, glucose utilisation and glucose oxidation were significantly increased 2.5- and 2.7-fold, respectively. When islets were incubated with both radiolabelled glucoses simultaneously, the rate of glucose oxidation was shown to be directly proportional to the rate of glucose utilisation. The relationship between glucose utilisation and glucose oxidation was similar in fetal and neonatal islets.(ABSTRACT TRUNCATED AT 250 WORDS)

THE PROTECTIVE EFFECT OF VERAPAMIL ON MOUSE ISLETS TRANSPLANTED UNDER THE KIDNEY CAPSULE1

Islets from normal NMRI mice were transplanted under the kidney capsule of syngeneic recipients. The graft-bearing mice were divided into 4 groups treated daily with cremophor alone (control), cyclosporine (25 mg/kg body wt), CsA in combination with the calcium antagonist verapamil (0.4 mg/kg), or verapamil alone. After 3 weeks the grafts were removed, analyzed for insulin secretory dynamics in a perifusion system, and extracted for their contents of insulin. The graft insulin content was significantly decreased by CsA, an effect counteracted by verapamil. As compared with controls, all treatments increased the basal insulin at 2.8 mmol/L glucose. CsA together with verapamil enhanced the biphasic secretory response to 16.7 mmol/L glucose, whether expressed per graft or per unit of insulin content. The glucose-stimulated insulin release per graft was greater after combining CsA with verapamil than after CsA alone. It is concluded that CsA has adverse effects on islets transplanted to the kidney, and that these effects can be ameliorated by combining the immunosuppressant with verapamil.

Chronic perifusion of rat islets with palmitate suppresses glucose-stimulated insulin release.

To test the hypothesis that the high circulating FFA levels in the diabetes of obesity could contribute to the altered dynamics of insulin secretion seen in that condition, insulin release was measured in isolated perifused rat islet cells, without or with added palmitate. Acutely, as in other systems, palmitate (1 mM) stimulated insulin release. Palmitate (1 mM) suppressed both first and second phase insulin release after 2, 3, or 4 h of perifusion, but not after 1 h. No significant effect was noted with 0.3 mM palmitate, and the effect was maximal at 1 mM. The stimulatory effects of arginine were essentially unaffected. Tolbutamide (1 mM) reversed or counteracted the effect. Glucose oxidation was suppressed in islets incubated with 1 mM palmitate for 4 h. Inhibitors of fat oxidation, alpha-bromostearate (1 mM) and methyl-3-tetradecylglycidate (100 microM) reversed the effects of palmitate on glucose-stimulated insulin release and glucose oxidation. Thus, prolonged incubation of rat islet cells with 1 mM palmitate could suppress the glucose-stimulated release of insulin from perifused rat islets. This suppression could be reversed by inhibitors of fat oxidation. This supports the hypothesis that elevated FFA levels and/or increased fat oxidation could contribute to the altered dynamics of insulin secretion in obese diabetics by fuel antagonism as well as the previously documented suppression of peripheral glucose uptake and stimulation of hepatic gluconeogenesis and may be a key link between obesity and the development of diabetes.