Nitric oxide is not involved in the initiation of insulin secretion from rat islets of Langerhans

Summary The involvement of nitric oxide as an intracellular messenger in the control of insulin secretion from pancreatic Beta cells was studied in rat islets of Langerhans by measuring: (i) nitric oxide generation in response to physiological insulin secretagogues; (ii) the effects of inhibitors of nitric oxide synthesis on insulin secretory responses to physiological secretagogues, and on insulin synthesis; (iii) changes in islet cyclic guanosine monophosphate in response to secretagogues; (iv) the effects of exogenous cyclic guanosine monophosphate and dibutyryl cyclic guanosine monophosphate on insulin secretion from electrically permeabilised islets and from intact islets, respectively. These studies produced no evidence that nitric oxide generation is required for the initiation of insulin secretion by common secretagogues. However, the results of our experiments suggest that the generation of nitric oxide may be involved in long-term, glucose-dependent increases in cyclic guanosine monophosphate content of islet cells, although the physiological relevance of these changes requires further investigation.     

Hyperglycaemia compensates for the defects in insulin-mediated glucose metabolism and in the activation of glycogen synthase in the skeletal muscle of patients with Type 2 (non-insulin-dependent) diabetes mellitus

Summary Insulin resistance and a defective insulin activation of the enzyme glycogen synthase in skeletal muscle during euglycaemia may have important pathophysiological implications in Type 2 (non-insulin-dependent) diabetes mellitus. Hyperglycaemia may serve to compensate for these defects in Type 2 diabetes by increasing glucose disposal through a mass action effect. In the present study, rates of whole-body glucose oxidation and glucose storage were measured during fasting hyperglycaemia and isoglycaemic insulin infusion (40 mU·m^–2min^–1, 3 h) in 12 patients with Type 2 diabetes. Eleven control subjects were studied during euglycaemia. Biopsies were taken from the vastus lateralis muscle. Fasting and insulin-stimulated glucose oxidation, glucose storage and muscle glycogen synthase activation were all fully compensated (normalized) during hyperglycaemia in the diabetic patients. The insulin-stimulated increase in muscle glycogen content was the same in the diabetic patients and in the control subjects. Besides hyperglycaemia, the diabetic patients had elevated muscle free glucose and glucose 6-phosphate concentrations. A positive correlation was demonstrated between intracellular free glucose concentration and muscle glycogen synthase fractional velocity insulin activation (0.1 mmol/l glucose 6-phosphate: r=0.65, p<0.02 and 0.0 mmol/l glucose 6-phosphate: r= 0.91, p<0.0001). In conclusion, this study indicates an important role for hyperglycaemia and elevated muscle free glucose and glucose 6-phosphate concentrations in compensating (normalizing) intracellular glucose metabolism and skeletal muscle glycogen synthase activation in Type 2 diabetes.     

Insulin binding to trophoblast plasma membranes and placental glycogen content in well-controlled gestational diabetic women treated with diet or insulin,in well-controlled overt diabetic patients and in healthy control subjects

Summary Insulin binding to trophoblast plasma membranes and the placental glycogen content were measured in twelve healthy women, in eleven well-controlled gestational diabetic women who were treated either with diet alone (n=4) or with insulin (n=7) and in 18 women with well-controlled overt diabetes mellitus (six White B; four White C; eight White D). The competitive binding assay was carried out with 22 concentrations of unlabelled insulin. Binding data were analysed by a non-linear direct model fitting procedure assuming one non-cooperative binding site. Maximum specific binding was unchanged in the total collective of gestational diabetic women, but was decreased by 30% in those treated with diet (6.2±2.2%) and increased by 90% in insulin-treated women (16.4±10.2%) as compared to the control subjects (8.7±2.5%). The diet-treated women had only 40% as many and those treated with insulin had more than twice as many receptors compared to control subjects on a per mg protein basis and if expressed per total placenta. In patients with overt diabetes mellitus maximum specific binding (18.5±10.6 %) was higher (p<0.05) due to more receptors compared to control subjects but was similar to the insulin-treated gestational diabetic patients. Maximum specific binding and receptor concentrations did not correlate linearly with maternal plasma insulin levels. Receptor affinities were virtually similar in all groups (1.8·10⁹ l/mol). The placental glycogen content was reduced (p<0.05) to about 80% of that of control subjects in the diet-treated collective, whereas it was unchanged compared to control subjects in the insulin-treated gestational diabetic women despite a 40% increase (p<0.001) of the maternal-to-cord serum glucose ratio. In overt diabetic patients the maternal-to-cord serum glucose ratio and the placental glycogen content were higher (p<0.05) than in the control subjects. We conclude that trophoblast plasma membranes from gestational diabetic women treated with diet alone express less and those from women treated with insulin express more insulin receptors than those from a healthy control group in vitro. These differences could not have been disclosed without consideration of the mode of treatment. Trophoblast plasma membranes from overt diabetic women have more insulin receptors than those from healthy control subjects.     

Acute actions of insulin-like growth factor II on glucose metabolism in adult rats

Summary The metabolic potency of recombinant human insulin-like growth factor II was studied in anaesthetized adult rats by obtaining dose-response curves for the hypoglycaemic action and for the stimulation of glucose metabolism during euglycaemic clamping. Compared to insulin, about 50 times higher doses of insulin-like growth factor II were required to result in identical in vivo responses, with half-maximally effective serum concentrations for the stimulation of glucose disposal during clamp studies of about 0.8 and 50 pmol/ml, respectively. A similar difference in potency was observed for the dose-dependent stimulatory actions on glucose metabolism in individual target tissues. Half-maximally effective serum concentrations in the range of 0.8 to 3.0 pmol/ml for insulin and of 40 to 70 pmol/ml for insulin-like growth factor II were seen to be required for 2-deoxyglucose uptake, glycogen formation in skeletal muscle and lipogenesis in epididymal fat. Maximal responses were identical with both peptides. These data suggest that in vivo acute metabolic actions of insulin-like growth factor II on carbohydrate metabolism occurred through insulin receptors.     

高血压病患者血清瘦素含量与胰岛素抵抗水平的相关性研究

目的：探讨高血压病患者血清瘦素水平与胰岛素抵抗的关系。方法：测定217例高血压病患者(男92例，女125例)的空腹血清瘦素含量、空腹血糖、胰岛素、收缩压、舒张压和体质量指数(BMI)，稳态模式评估法计算胰岛素抵抗指数(HOMA-IR)。分析瘦素与其他各项参数的相关性。结果：以HOMA—IR的25％位点，作为判断胰岛素抵抗的切割点，把高血压病患者分为胰岛素抵抗组(IR)和胰岛素敏感组(IS)，血清瘦素浓度IR组显著高于IS组(P＜0．05)。血清瘦素浓度与HOMA—IR呈显著正相关(男性r＝0．407，P＜0．01；女性r＝0．254，P＜0．01)；校正年龄和BMI后，男性组两者仍呈显著正相关(r＝0．219，P＜0．05)，女性组两者无相关；逐步回归分析显示，男性组HOMA—IR为血清瘦素浓度的独立预测因素。结论：男性高血压病患者血清瘦素浓度与胰岛素抵抗直接相关，女性则无直接相关性。性别差异的机制有待进一步探讨。     

体外循环对瓣膜置换术病人血细胞胰岛素受体和红细胞ATP含量的影响

目的：观察体外循环（ＣＰＢ）对１０例瓣膜置换术病人全血细胞胰岛素受体和红细胞ＡＴＰ含量的影响。方法：利用放射配体结合试验，测定全血细胞胰岛素受体密度和亲和力；用高效液相色谱法测定红细胞ＡＴＰ含量，同时监测血糖和胰岛素浓度。结果：转流３０分钟，血细胞高亲和胰岛素受体（Ｒ１）密度明显增加（Ｐ＜０．０１），亲和力（Ｋ１）明显降低（Ｐ＜０．０１），低亲和胰岛素受体（Ｒ２）密度也明显增加（Ｐ＜０．０１），但亲和力（Ｋ２）变化不大（Ｐ＞０．０５）；停机３０分钟，上述变化有所恢复，但未到转流前的水平。转流３０分钟红细胞ＡＴＰ含量明显降低（Ｐ＜０．０１），并持续到停机后３０分钟，同时伴随血糖明显升高（Ｐ＜０．０１），胰岛素／血糖比值明显降低（Ｐ＜０．０１）。结论：ＣＰＢ可致血细胞胰岛素受体密度增加而亲和力下降，以及红细胞ＡＴＰ含量下降。     

胰岛素泵的临床应用进展

综述了胰岛素泵在不同类型及不同情况糖尿病病人中的应用,列举了胰岛素泵临床应用中的常见问题。     

应用荧光探针H2DCF-DA检测光照致细胞内活性氧产生的初步研究

目的应用荧光显微镜及新型荧光探针H2DCF-DA检测在光源照射过程中人脐静脉血管内皮细胞(ECV304)内活性氧的产生情况。方法将ECV304细胞接种于35mm培养皿中,24h后加入H2DCF-DA,使其终浓度为10μmol/L,孵育30min。利用荧光显微镜的激发光源作为照射光源,在采集荧光图像的同时完成光源照射,光源输出波长范围为460～490nm,功率密度约为100mW/cm2。连续采集DCF的荧光图,观察细胞内DCF荧光的变化情况,采用计算机图像处理和分析技术,求得细胞内不同照射时间点DCF平均荧光强度,进而得到平均荧光强度-时间曲线。另外,使用线粒体特异标记探针MitoFluorRed589与H2DCF-DA共同孵育细胞,分别采集同一细胞的DCF的荧光图和MitoFluorRed589的荧光图,并利用像素-荧光强度分析方法来确定DCF荧光在细胞内的分布位置。结果在光源照射的开始阶段,ECV304细胞内的DCF荧光强度迅速增加,在第10s时便上升至第2s时的2.2倍,但是随着照射时间逐渐延长,荧光强度增幅逐渐变小,到第60s时上升至第2s时的4.7倍。观察时间进一步延长,DCF的荧光强度的变化似乎进入平台期,继而开始出现下降。考察DCF荧光在ECV304细胞内的分布位置主要通过比较细胞内不同区域的I1/I2值,通过图像分析与计算得到线粒体区、细胞核区以及细胞质非线粒体区内I1/I2值分     

血清瘦素水平的影响因素及相关性分析

目的探讨血清瘦素水平的影响因素及相关性分析.方法从2003年3～8月门诊体验人群中随机抽取标本150人,并排除糖尿病及高血压,测定FBS、血脂水平、血清瘦素水平(LEP)、胰岛素水平(INS),瘦素、胰岛素测定均采用放射免疫方法.胰岛素敏感性以敏感指数(IAI)评价.结果血清瘦素水平女性明显高于男性;相关分析显示血清瘦素水平与性别(SEX)、年龄(AGE)、体重指数(BMI)、INS显著正相关(r分别为0.429,0.329,0.249,0.322,P＜0.05);与LOGIAI显著负相关(r=0.322,P＜0.05),与TC,TG无明显相关;在调整年龄、BMI后,多远逐步回归分析显示血清瘦素水平仍与INS,LOGIAI显著相关.结论血清瘦素水平与TC,TG均无相关,提示高脂血症患者血清瘦素水平与正常人群比较无明显改变;血清瘦素水平与LOGIAI负相关,高瘦素水平人群胰岛素敏感性降低、存在胰岛素抵抗,提示瘦素-胰岛素轴的存在,瘦素是胰岛素抵抗的一个独立危险因素.肥胖患者存在高瘦素血症、瘦素抵抗.如果能弄清瘦素、胰岛素抵抗、肥胖之间的相互作用关系及因果关系,可能对瘦素抵抗、胰岛素抵抗相关痰病的防治有一定的意义.