早期胰岛素分泌降低是正常血糖人群糖代谢异常的主要危险因素

目的 评价早期胰岛素分泌降低及胰岛素抵抗在糖代谢异常发病中的作用,探讨正常血糖人群发生糖代谢异常的主要危险因素.方法 对来自78个2型糖尿病家系的成员进行口服葡萄糖耐量试验(OGTT),选择其中年龄在30岁以上的糖耐量正常(NGT)人群[空腹血糖(FPG)<6.1mmol/L,糖负荷后2h血糖(2hPG)<7.8 mmol/L]共118人进行随访,在4-7年后复查OGTT,确定其糖代谢状态,分别以糖负荷30min净增胰岛素与净增葡萄糖的比值(AINS30/APG30)评估早期胰岛素分泌能力,以稳态模型法胰岛素抵抗指数(HOMA-IR)估测胰岛素抵抗状况,以稳态模型法β细胞功能指数(HOMA-B)估测B细胞功能,分析其对糖代谢状态转归的影响.结果 来自78个2型糖尿病家系的118人NGT人群随访4～7年后,66人仍为NGT,52人出现糖耐量恶化,其中糖尿病11人,糖尿病前期41人.分别以HOMA-IR及AINS30/APG30的中位数为切点将这118人人群分4组,4组中糖代谢异常的发生率分别为23.1%、36.4%、45.5%、73.1%,早期胰岛素分泌降低且胰岛素抵抗较重者糖代谢异常发生率较高(P<0.05);Logistic回归分析显示基线时早期胰岛素分泌能力与糖耐量恶化的发生呈明显负相关,而年龄、性别、胰岛素抵抗状况、β细胞功能均与糖调节受损的发生无显著相关性.结论 早期胰岛素分泌降低是正常血糖人群发生糖代谢异常的主要危险因素.     

The regulation of glucose-induced insulin secretion by Pre-stimulus glucose level and tolbutamide in normal man

Summary The relationship between the pre-stimulus glucose level and immunoreactive insulin responses to a glucose challenge (20-g IV) was studied in normal subjects. When the steady-state pre-stimulus glucose concentration was lowered by a 0.33 mU· kg^-1· min^-1 insulin infusion or raised by a 900mg/ min glucose infusion, no effect on first phase insulin secretion (mean 3–5 min insulin level) was observed. In contrast, the second phase response (10–60 min insulin area after glucose pulse) to intravenous glucose fell during insulin infusion and increased during the glucose infusion. Overall, a linear relationship was found between the change of pre-stimulus glucose level from the control to that during the insulin or glucose infusion and the change in second phase response (r=0.65, n = 14, p<0.02). The effect of tolbutamide infusion (7 mg·m^-2· min^-1) when compared with saline control was to increase both first phase (+54 ±13 mU/1, n=8, p <0.001, mean±SEM) and second phase (+972±256mU · mur^-1 · 1^-1, P<0.01) insulinsecretion. It is concluded that the first phase response to a glucose pulse is independent of the steady-state pre-stimulus glucose concentration and is directly enhanced by tolbutamide; in contrast, second phase is related to both the steady-state pre-stimulus glucose level and tolbutamide. These findings suggest that changes in basal or pre-stimulus plasma glucose during therapy with sulphonylurea drugs may be expected to influence the second phase insulin responses to glucose challenge.     

Effects of alloxan on glucose-stimulated insulin secretion,glucose metabolism,and cyclic adenosine 3′, 5′-monophosphate levels in rat isolated islets of Langerhans

Summary Insulin secretion was stimulated and cyclic adenosine 3, 5-monophosphate (cAMP) levels were elevated in isolated rat islets by 27.5 mmol/l glucose. Alloxan caused a dose-dependent decrease in both variables with complete obliteration of insulin release at a concentration of 1.25 mmol/l. D-glucose, in the presence or absence of extracellular calcium, or 3-0-methyl-D-glucose (both at 27.5 mmol/l) protected completely against the effects of alloxan on both glucose-induced insulin release and cAMP levels. 3-0-Methylglucose did not stimulate insulin secretion or elevate cAMP and did not interfere with glucose-stimulated secretion or elevation of cAMP. When glucose-stimulated insulin release was abolished by alloxan, the metabolism of glucose, determined by the rate of³H₂O formation from [5-³H] glucose, was depressed by 20%. It is concluded that alloxan altered the adenylate cyclase system such that it could no longer be stimulated by glucose. Glucose-stimulated insulin secretion or elevation of cAMP did not appear essential for glucose to protect against alloxan. Protection by 3-0-methylglucose did not appear to be mediated through an alteration of cAMP metabolism. Alloxan did not inhibit glucose-induced insulin secretion by grossly altering glycolysis.     

Glucose levels and insulin secretion during a 75 g glucose challenge test in normal pregnancy

Objectives. The aim of the study was to evaluate glucose levels and insulin secretion early in pregnancy and at a time when gestational diabetes mellitus frequently occurs in order to define reference values for glucose tolerance during pregnancy. The results were also related to maternal factors that might identify subjects at risk of developing gestational diabetes mellitus as well as foetal factors that might be a result of impaired glucose tolerance during pregnancy. Design. A prospective study. Setting. All Caucasian women attending one antenatal out-patient care unit were offered a 75 g oral glucose tolerance test at the 17th and 32nd week of gestation. Subjects. A total of 586 consecutive pregnant women were included in the study. All 586 women were examined by repeated blood glucose measurements and 298 agreed to perform oral glucose tolerance tests as well. Main outcome measures. Venous whole blood glucose values were measured in the fasting state and in samples obtained 15, 30, 45, 60, 75, 90 and 120 min after oral intake of 75 g glucose. Serum insulin and C-peptide were also measured at these times. In all subjects, a random blood glucose sample was taken at the first visit, and thereafter at the 20th, 30th and 36th week of gestation. Information was also obtained from all subjects regarding body mass index, weight gain during pregnancy, smoking habits, family history of diabetes and hypertension, hypertension during pregnancy, past obstetric history, parity, and fetal outcome. Results. The glucose tolerance was significantly impaired at the 32nd week of gestation compared with the 17th week of gestation. The mean +2SD 2h glucose value during the oral glucose tolerance test at the 32nd week of gestation was 8.0 mmol L^?1. Impaired glucose tolerance was characterised by increased insulin resistance, with a significant rise in serum insulin and C-peptide concentrations and in the insulin/glucose index during the oral glucose tolerance test at the 32nd week of gestation. Maternal factors associated with an impaired glucose tolerance were a family history of diabetes mellitus, smoking, a weight gain more than 18 kg during pregnancy, and glucosuria, while a family history of hypertension and hypertension present during pregnancy were not. Foetal factors that might be a result of impaired glucose tolerance during pregnancy, e.g. macrosomia and prematurity as well as complicated deliveries such as vacuum extraction/forceps or Caesarean section, all tended to be associated with higher blood glucose values. The same pattern was seen when the Apgar score was <7. Conclusions. The results from this study show that the present cut-off values for diagnosis of gestational diabetes mellitus should be revised. Even if some maternal factors might indicate an increased risk for impaired glucose tolerance during pregnancy, they are probably not enough to detect women with gestational diabetes mellitus. Therefore, a screening programme for gestational diabetes should be considered.     

Measurement of glucose metabolism and insulin secretion during normal pregnancy and pregnancy complicated by gestational diabetes

Summary Gestational diabetes affects 2–3% of pregnant women and is associated with foetal complications including macrosomia and an increased likelihood of developing diabetes in later life. We have therefore studied seven women with gestational diabetes and five control women both during the third trimester of pregnancy and again 2–3 months post-partum, using the minimal model analysis of the frequently sampled labelled ([6, 6-²H₂]-glucose) intravenous glucose tolerance test. Glucose tolerance (glucose K_d) was significantly reduced in the women with gestational diabetes compared with the normal pregnant women both in pregnancy (1.16±0.11 vs 1.78±0.23%/min; p<0.05) and post-partum (1.47±0.22 vs 2.59±0.43%/min; p<0.05) and increased significantly in the control women after delivery (p<0.05). Glucose effectiveness was not significantly different between the women with gestational diabetes and the control group either during or after pregnancy. Insulin sensitivity was significantly lower during pregnancy than after delivery in the women with gestational diabetes (p<0.05). There was no significant difference in basal insulin secretion in the two groups during pregnancy or post-partum. However, during pregnancy the control subjects significantly increased (p<0.001) their insulin secretion over a period of 20 min in response to an intravenous glucose tolerance test (96.2±42.7 pmol/kg) compared with post-partum values (58.3±25.2 pmol/kg) while in the women with gestational diabetes insulin secretion was similar in pregnancy (65.5±9.3 pmol/kg) and after delivery (57.7±15.7 pmol/kg). These data suggest that the glucose intolerance in gestational diabetes compared to normal pregnancy is due to reduced insulin sensitivity and an impaired ability in gestational diabetes to increase insulin secretion in response to glucose.Abbreviations BMI Body mass index - GCMS gas chromatography mass spectrometry - GDM gestational diabetes mellitus - HOMA homeostasis model assessment - IVGTT intravenous glucose tolerance test - OGTT oral glucose tolerance test - Sab above basal insulin secretion - Sb basal insulin secretion - K_d glucose disappearance - CV coefficient of variation - AIR_glucose acute insulin response to glucose - SI insulin sensitivity index - SG glucose effectiveness     

正常糖耐量人群中血压与胰岛素抵抗及胰岛素分泌关系研究

目的研究血压与胰岛素敏感性和胰岛B细胞功能之间的关系。方法采用多阶段分层整群随机抽样方法对江苏省内人群进行研究,根据口服葡萄糖耐量试验结果选取18岁以上正常糖耐量人群952例,根据血压不同,分为正常血压组、正常高值组、1级高血压组、2级高血压组、3级高血压组。胰岛素敏感性采用ISIM及1/HOMA-IR评价;胰岛B细胞功能采用HOMA-β、InsAUC30/GluAUC30和InsAUC120/GluAUC120评估。结果同正常血压组相比,正常高值组和1、2、3级高血压组的1/HOMA-IR分别下降11.1%、14.8%、24.1%、33.3%(P<0.001),ISIM分别下降10.3%、15.5%、27.6%、37.1%(P<0.001);InsAUC30/GluAUC30指数分别升高11.1%、41.3%、42.9%、101.2%(P<0.001),InsAUC120/GluAUC120分别升高13.2%、46.5%、54.2%、96.9%(P<0.001);5组间的HOMA-β有上升趋势,但差异无统计学意义。处置指数DI(包括基础时相DI0、早时相DI30、总时相DI120)在5组别间均没有明显变化。结论正常糖耐量人群中,随着血压升高,胰岛素敏感性逐渐下降,出现胰岛素抵抗,胰岛素分泌逐渐上升,尚未出现胰岛分泌功能的缺陷。     

Differential mechanisms of glucose and palmitate in augmentation of insulin secretion in mouse pancreatic islets

Aims/hypothesis. To assess the possible importance of saturated fatty acids in glucose amplification of K⁺ _ATP channel-independent insulin secretion. Methods. Insulin release from perifused pancreatic islets of NMRI mice was determined by radioimmunoassay. Results. In the presence of K⁺ (20 mmol/l) and diazoxide (250 μmol/l), which stimulates Ca²⁺ influx and opens K⁺ _ATP channels, palmitate (165 μmol/l total; 1.2 μmol/l free) increased insulin secretion at 3.3, 10 and 16.7 mmol/l glucose while glucose (10; 16.7 mmol/l) did not increase insulin secretion. In the presence of K⁺ (60 mmol/l) and diazoxide (250 μmol/l), glucose (10; 16.7 mmol/l) stimulation of K⁺ _ATP channel-independent insulin secretion increased, whereas the effectiveness of palmitate (165 μmol/l total; 1.2 μmol/l free) on insulin secretion at both 3.3, 10 or 16.7 mmol/l glucose was reduced. Palmitate thereby mimicked the stimulatory pattern of the protein kinase C activator, 12-O-tetradecanoylphorbol 13-acetate (0.16 μmol/l), which also failed to increase insulin secretion at maximum depolarising concentrations of K⁺ (60 mmol/l). Furthermore, the protein kinase C inhibitor calphostin C (1 μmol/l), led to a complete suppression of the effects of both palmitate (165 μmol/l total; 1.2 μmol/l free) and myristate (165 μmol/l total; 2.4 μmol/l free) stimulation of glucose (16.7 mmol/l)-induced insulin secretion. Calphostin C (1 μmol/l), however, failed to affect insulin secretion induced by glucose (16.7 mmol/l). Conclusion/interpretation. These data suggest that glucose could increase insulin secretion independently of saturated fatty acids like palmitate and myristate, which amplify glucose-induced insulin secretion by activation of protein kinase C. [Diabetologia (2001) 44: 738–746] Received: 30 October 2001 and in revised form: 31 January 2001     

Decreased insulin action and insulin secretion predict the development of impaired glucose tolerance

Summary The relative importance of insulin resistance and abnormal insulin secretion as risk factors for the development of impaired glucose tolerance (IGT) is controversial. Few prospective data are available on metabolic precursors of IGT. We examined the relation of fasting serum insulin level (as a marker of insulin resistance) and change in insulin/glucose ratio (ΔI ₃₀/ΔG₃₀) over the first 30 min after glucose ingestion (as a marker of insulin secretion) as predictors of the 7-year development of IGT in 839 Mexican Americans and non-Hispanic whites with normal glucose tolerance at baseline from the San Antonio Heart Study. IGT eventually developed in 148 subjects. When modelled separately, fasting serum insulin (odds ratio (OR)=2.60,95 % confidence interval (CI)=1.58,4.28,p<0.005), but not ΔI ₃₀/ΔG₃₀ (OR=0.80, 95 % CI=0.50,1.27,p=0.339) predicted the development of IGT. However, when both variables were included in the same logistic regression model, fasting serum insulin (OR=3.50, 95 % CI=1.97,6.21,p<0.001) and low ΔI ₃₀/ΔG₃₀ (OR=0.48, 95 % CI=0.28,0.82,p=0.008) both predicted IGT. These results were basically unchanged after further adjustment for obesity, body fat distribution and fasting plasma glucose level. We conclude that both decreased insulin secretion (as assessed by low ΔI ₃₀/ΔG₃₀) and increased insulin resistance (as assessed by fasting serum insulin) predict the development of IGT and are thus early precursors of non-insulin-dependent diabetes mellitus; further studies of insulin secretion should take into account the level of basal insulin resistance.     

Evidence for priming and inhibitory effects of glucose on insulin secretion from isolated islets of langerhans

Summary Biphasic insulin secretion from perifused rat islets of Langerhans was affected in three ways by the islet glucose environment prior to stimulation, (i) The secretory response to glucose was diminished if the basal concentration of glucose in the medium was reduced from 5.5 to 2.7 mmol/l for 2 h prior to stimulation. First phase secretion was affected more than the second, (ii) Secretion was potentiated if islets had been previously exposed to a stimulatory concentration of glucose of 22.2 mmol/l. Again first phase secretion was particularly affected and there was a positive correlation between the magnitude of the secretory response and the duration of the initial stimulus, (iii) In contrast, both phases of secretion were proportionately reduced if islets had been previously exposed to stimulatory concentrations of glucose of 8.3 mmol/l.     

Divergent effect of glucagon antibodies on arginine and glucose-stimulated insulin secretion in the rat

Summary The effects of glucose and arginine on insulin secretion in the presence of glucagon antibodies were investigated in rats in vivo. In contrast to controls, animals given glucagon antibodies showed an inhibition of arginine-stimulated (p < 0.001), but not glucose-stimulated, insulin secretion. That these effects were not due to incomplete neutralisation of endogenous glucagon is evidenced by the presence of large antibody excess throughout the duration of the experiments. Both the glucagonotropic effect of arginine (319 ± 60ng/l, p < 0.01) and the insulinotropic effect of exogenous glucagon (8.3 ± 0.8 g/l, p < 0.001) were demonstrable under our experimental conditions in the absence of exogenous glucagon antibodies. These observations suggest that different mechanisms are involved in the stimulation of insulin release by arginine and by glucose, and that glucagon may play an important physiological role in the mediation and regulation of insulin secretion by secretogogues, such as arginine.     

Effect of high sucrose diet on insulin secretion and insulin action: a study in the normal rat

Summary The effects of chronic high sucrose feeding for 1 month on in vivo and in vitro insulin secretion and on in vivo insulin action were studied in normal male rats. As compared to the standard chow diet, the high sucrose diet induced excess in vivo insulin response to an intravenous glucose load; the high sucrose diet also slightly improved glucose tolerance, as demonstrated by significantly higher rate of glucose disappearance (p<0.02). The increased insulin secretion in response to glucose in vivo seems to be related to an hyper-reactivity of the pancreatic B cell to glucose, since it was still observed in vitro with the isolated perfused pancreas preparation. By contrast, B cells of sucrose-fed rats exhibited in vitro a normal response to arginine and a significantly lowered (p<0.05) response to acetylcholine. The insulin action in the sucrose-fed rats was quantified in vivo with the insulin-glucose clamp technique. The effects of different concentrations of insulin on glucose production and glucose utilization were studied in anaesthetized rats while in the postabsorptive state. The basal glucose utilization was found significantly higher (p<0.001) in sucrose-fed rats. During the clamp studies the glucose utilization induced by submaximal (400 U/ml) or maximal (7500 U/ml) insulin levels was significantly more important (p<0.02) in the sucrose-fed rats than in the chow-fed rats. This suggests that insulin-mediated glucose uptake is enhanced over a large range of plasma insulin levels in the sucrose-fed rats. In the basal state hepatic glucose production was significantly higher (p<0.001) in sucrose-fed rats. During the clamp studies, the suppression of glucose production induced by submaximal or maximal insulin levels was significantly less effective (p<0.05) in the sucrose-fed rats as compared to chow-fed rats, thus suggesting that the liver becomes resistant to insulin action after sucrose feeding.     

The priming effect of glucose on insulin secretion from isolated islets of Langerhans

Summary Biphasic insulin secretion from perifused rat islets of Langerhans was enhanced if islets had previously been stimulated with glucose 16.6 mmol/l. The priming effect of glucose was reduced if mannoheptulose (16.6 mmol/l), deuterium oxide (D₂O; 98% v/v) or adrenaline (10mol/l) was included in the medium during the initial stimulation period, or if Calcium was omitted. Glyceraldehyde (16.6 mmol/l) but not theophylline (5 mmol/l) could substitute for glucose during the initial stimulation and make islets more responsive to subsequent stimulation. The results suggest that the priming effect of glucose on insulin secretion may be related to 1) glucose metabolism and 2) Ca fluxes in the B cell and the consequent activation of the microtubular system. Neither the generation of intracellular cyclic AMP nor the release of insulin per se appears to be involved in the priming process.     

Inhibition of insulin secretion by cerulenin might be due to impaired glucose metabolism

BACKGROUND: Cerulenin, an inhibitor of protein acylation, has been used as a tool to study the potential role of protein acylation in a variety of activities in different cells, and in stimulus-secretion coupling in pancreatic islets and clonal beta-cells. METHODS: In the present study we investigated its effects on stimulated insulin secretion, glucose metabolism and utilization, oxygen consumption and ATP levels. RESULTS: In isolated rat pancreatic islets, cerulenin pre-treatment (100 microM) inhibited insulin secretion in response to glucose, and to the non-hydrolysable analogue of leucine, aminobicyclo-[2,2,1]heptane-2-carboxylic acid (BCH). These data are in accord with the hypothesis that protein acylation could be involved in the stimulation of insulin secretion. However, we also found that cerulenin profoundly decreased glucose oxidation, glucose utilization, oxygen consumption and ATP levels. Consequently, decreased metabolism provides an alternative mechanism to inhibition of protein acylation that could explain the inhibition of insulin secretion by cerulenin. CONCLUSIONS: Inhibition of insulin secretion by cerulenin can no longer be taken as evidence in favour of a role for protein acylation in the control of insulin release. As protein acylation is known to be involved in the normal functioning of proteins in stimulus-secretion coupling and exocytosis, more direct approaches to understand its role(s) are required.     

Cellular characterization of pituitary adenoma cell line (AtT20 cell) transfected with insulin, glucose transporter type 2 (GLUT2) and glucokinase genes: Insulin secretion in response to physiological concentrations of glucose

Summary We investigated the mechanisms of insulin secretion by transfecting into a pituitary adenoma cell line (AtT20) a combination of genes encoding human insulin (HI), glucose transporter type 2 (GLUT2) and glucokinase (GK), followed by studying the characteristics of these cells. In static incubation, a cell line transfected with insulin gene alone (AtT20HI) secreted mature human insulin but this was not in a glucose-dependent manner. Other cell lines transfected with insulin and GLUT2 genes (AtT20HI-GLUT2–3) or with insulin and GK genes (AtT20HI-GK-1) secreted insulin in response to glucose concentrations of only less than 1 mmol/l. In contrast, cell lines transfected with insulin, GLUT2 and GK genes (AtT20HI-GLUT2-GK-6, AtT20HI-GLUT2-GK-7 and AtT20HI-GLUT2-GK-10) showed a glucose-dependent insulin secretion up to 25 mmol/l glucose. Glucose utilization and oxidation were increased in AtT20HI-GLUT2-GK cell lines but not in AtT20HI, AtT20HI-GLUT2–3 and AtT20HI-GK-1 cells at physiological glucose concentrations, compared with AtT20 cells. Diazoxide, nifedipine and 2-deoxy glucose suppressed (p < 0.05) glucose stimulated insulin secretion in AtT20HI-GLUT2-GK-6 cells. Glibenclamide, KCl or corticotropin releasing factor (CRF) stimulated (p < 0.05) insulin secretion both in AtT20HI and AtT20HI-GLUT2-GK-6 cells. Insulin secretion stimulated by glibenclamide, KCl or CRF was further enhanced by the addition of 25 mmol/l glucose in AtT20HI-GLUT2-GK-6 cells but not in AtT20HI cells. In perifusion experiments, a stepwise increase in glucose concentration from 5 to 25 mmol/l stimulated insulin secretion in AtT20HI-GLUT2-GK cell lines but the response lacked a clear first phase of insulin secretion. Our results suggest that both GLUT2 and glucokinase are necessary for the glucose stimulated insulin secretion in at least rodent cell lines, and that other element(s) are necessary for a biphasic insulin secretion typically observed in beta cells. [Diabetologia (1998) 41: 1492–1501] Received: 9 February 1998 and in revised form: 19 May 1998     

基础及早期胰岛素分泌对2型糖尿病患者血糖水平的贡献

目的　探讨 2型糖尿病人群基础及早期胰岛素分泌对血糖水平的贡献。方法　 2型糖尿病患者 81例 ,测定标准餐试验 0、3 0、60、12 0min血浆葡萄糖及真胰岛素水平。计算胰岛素敏感性指数 (ISI)和早期胰岛素分泌 (ΔI3 0 /ΔG3 0 ) ,以评估机体胰岛素敏感性 ,以多因素回归方法评估早期及基础胰岛素分泌对2型糖尿病人群血糖变化的贡献。结果　多因素回归分析显示 ,ISI和ΔI3 0 /ΔG3 0 对血糖变化的贡献几乎相等。在标准餐试验各时点胰岛素值中 ,空腹及 60min血浆真胰岛素水平对血糖水平的变化起主要作用 ;空腹胰岛素对血糖曲线下面积的作用强于ΔI3 0 /ΔG3 0 的作用。结论　基础及早期胰岛素分泌对血糖水平的变化都有重要影响     

Daily rhythm of glucose-induced insulin secretion by isolated islets from intact and pinealectomized rat

It is well known that pinealectomy induces in rats a diminished glucose tolerance, insulin resistance, a reduction in GLUT4 content in adipose and muscular tissues, a decrease in hepatic and muscular glycogenesis, impairment of glucagon action and an increase in blood pyruvate concentration. In addition, it has been shown that melatonin suppresses insulin secretion in several experimental conditions. The objective of the present study was to investigate the daily rhythm of glucose-induced insulin secretion and glucose oxidation by isolated pancreatic islets and to investigate the effect of chronic absence of melatonin (30 days of pinealectomy) on this rhythmic process. The data obtained confirmed the presence of a strong 24-hr rhythm of insulin secretion by isolated pancreatic islets. In addition, it was demonstrated that the glucose-metabolizing ability of the B-cell follows a daily rhythm phase locked to insulin secretion rhythm. Most interesting, however, was the demonstration that the daily rhythmic processes of insulin secretion and B-cell -[U-14C]-glucose oxidation by isolated pancreatic islets is completely modified by the chronic absence of the pineal gland. Thus, pinealectomy induced in all groups an increase in 24-hr mean glucose-stimulated insulin secretion and [U-14C]-glucose oxidation, in addition to some alterations in the rhythmic amplitude and a remarkable phase-advancing of the daily curves for 8.3 mm glucose (a condition similar to that observed in fed animals and where the B-cells are supposedly more active). These observations strongly suggest that the presence of the pineal gland may be necessary for the proper synchronization of these metabolic rhythms with other circadian rhythms like activity-rest and feeding.     

Properties of isolated human islets of langerhans: insulin secretion,glucose oxidation and protein phosphorylation

Summary In the present study, human islets were isolated by collagenase digestion from the pancreases of three kidney donors. Maintainance of the islets in tissue culture enabled insulin release, glucose oxidation and Ca²⁺-calmodulin-dependent protein phosphorylation to be determined using the same islets. Increasing glucose over a range 0–20 mmol/l resulted in a sigmoidal stimulation of insulin release (28.8±5.2 to 118.4±25.8 U-islet^–-h^–, n=10; threshold <4 mmol/l). There was a marked correlation between the insulin secretory response of the islets to glucose and their rate of glucose oxidation (5.9±0.3 at glucose 2 mmol/l up to 25.8±1.8 pmol-islet^–.h^– at 20 mmol/l, r = 0.98). N-acetylglucosamine (20 mmol/l) failed to elicit a secretory response from the islets. Stimulation of insulin secretion by glucose was dependent upon the presence of extracellular Ca²⁺. Extracts of the islets contained a Ca²⁺-calmodulin-dependent protein kinase which phosphorylated a 48-kdalton endogenous polypeptide. Myosin light-chain kinase activity was demonstrated in the presence of exogenous myosin light chains. This report demonstrates for the first time the sigmoidal nature of glucose-stimulated insulin release from isolated human islets, and its correlation with enhanced glucose oxidation. Furthermore, this is the first report of the presence of Ca²⁺-dependent protein kinases in human islets.     

Soybean oil treatment impairs glucose-stimulated insulin secretion and changes fatty acid composition of normal and diabetic islets

We investigated the effect of sub-chronic soybean oil (SO) treatment on the insulin secretion and fatty acid composition of islets of Langerhans obtained from Goto-Kakizaki (GK), a model of type 2 diabetes, and normal Wistar rats. We observed that soybean-treated Wistar rats present insulin resistance and defective islet insulin secretion when compared with untreated Wistar rats. The decrease in insulin secretion occurred at all concentrations of glucose and arginine tested. Furthermore we observed that soybean-treated normal islets present a significant decrease in two saturated fatty acids, myristic and heneicosanoic acids, and one monounsaturated eicosenoic acid, and the appearance of the monounsaturated erucic acid. Concerning diabetic animals, we observed that soybean-treated diabetic rats, when compared with untreated GK rats, present an increase in plasma non-fasting free fatty acids, an exacerbation of islet insulin secretion impairment in all conditions tested and a significant decrease in the monounsaturated palmitoleic acid. Altogether our results show that SO treatment results in a decrease of insulin secretion and alterations on fatty acid composition in normal and diabetic islets. Furthermore, the impairment of insulin secretion, islet erucic acid and fasting plasma insulin levels are similar in treated normal and untreated diabetic rats, suggesting that SO could have a deleterious effect on β-cell function and insulin sensitivity.     

Transgenic overexpression of human islet amyloid polypeptide inhibits insulin secretion and glucose elimination after gastric glucose gavage in mice

Summary Islet amyloid polypeptide (IAPP) is synthesized in islet beta cells and has been implicated in diabetes pathogenesis because it can inhibit insulin secretion and action and form fibrils leading to islet amyloidosis. Its physiological function has, however, not been established. We therefore examined insulin secretion and glucose elimination after i. v. or gastric gavage of glucose in transgenic mice overexpressing human IAPP (hIAPP) resulting in considerably increased circulating IAPP concentrations. The insulin response to and the glucose elimination after i. v. glucose (1 g/kg) were not different in transgenic mice compared with wild type animals, neither in males nor in females. In contrast, the insulin response to gastric glucose (150 mg/mouse) was reduced and the glucose elimination was inhibited in both male and female transgenic mice. The area under the 30 min insulin curve (AUC_insulin) was 21 ± 2 nmol/l in 30 min in transgenic males (n = 24) vs 43 ± 3 nmol/l in 30 min in wild type males (n = 26; p < 0.001) and the respective areas under the glucose curve (AUC_glucose) were 1.90 ± 0.12 and 1.62 ± 0.09 mol/l in 120 min (p < 0.05). Similarly, in females, the AUC_insulin was 17 ± 2 nmol/l in 30 min in transgenic mice vs 25 ± 3 nmol/l in 30 min in wild type mice (p < 0.05) and the respective AUC_glucose was 1.62 ± 0.7 and 1.12 ± 0.07 mol/l in 120 min (p < 0.001). Hence, endogenous hIAPP inhibits insulin secretion and glucose elimination after gastric glucose gavage in both male and female mice, indicating that overexpression of hIAPP could be a diabetogenic factor, via effects on the intestinal tract or the gut-islet axis or both. [Diabetologia (1998) 41: 1374–1380] Received: 31 March 1998 and in revised form: 15 June 1998