异搏定对四氧嘧啶损害大鼠胰岛β细胞的保护作用

本工作用四氧嘧啶(尾静脉注射)造成大鼠实验性糖尿病模型。若预先由腹腔注射异搏定(40mg/kg)则可使大鼠血糖水平明显降低,不产生糖尿病,注射四氧嘧啶后48h,血糖浓度的平均值由22.93±1.37mmol/L下降到8.79±0.83mmol/L。口服葡萄糖耐量试验观察到,经过异搏定处理的糖尿病大鼠,在注射四氧嘧啶后的48h,其胰岛素分泌功能较未经异搏定处理的糖尿病大鼠有明显的恢复。组织学切片也显示,胰岛β细胞内胰岛素分泌颗粒的含量在异搏定处理组较单独四氧嘧啶处理组明显增多。上述结果表明,预先注射异搏定能减轻四氧嘧啶对胰岛β细胞造成的急性损伤。     

铃蟾肽对四氧嘧啶引起的大鼠糖尿病的预防作用

本工作从三个不同的层次对铃蟾肽防止胰岛 B 细胞损伤的作用进行了研究:(1)在整体水平,预先注射铃蟾肽(50μg/kg,iv)可明显抑制单独给予四氧嘧啶(200mg/kg,s.c.)引起的大鼠血糖升高和血浆胰岛素水平下降的趋势。(2)在离体胰腺灌流实验发现,在四氧嘧啶之前预灌流铃蟾肽(10~(-2)mmol/L)可使胰腺对高糖刺激产生反应性分泌;而仅以四氧嘧啶灌流时,胰腺对高糖刺激无反应。(3)在离体胰岛水平,初步研究了在四氧嘧啶引起胰岛 B 细胞功能改变时,铃蟾肽对胰岛内胰岛素、胰高血糖素和生长抑素分泌的影响。结果表明,铃蟾肽可防止四氧嘧啶引起的胰岛素和生长抑素分泌的抑制及胰高血糖素分泌的增加趋势。     

消炎痛对四氧嘧啶引起的大鼠糖耐量和胰岛素分泌改变的影响

本实验以糖耐量为指标,观察了消炎痛抗四氧嘧啶引起的大鼠胰岛Ｂ细胞的损伤作用。皮下注射四氧嘧啶（１５０ｍｇ／ｋｇ）的大鼠控口灌注葡萄糖（５ｇ／ｋｇ以后,血糖浓度急剧升高并在灌胃后１８０ｍｉｎ仍继续升高。在葡萄糖刺激后血清胰岛素浓度无明显升高,未出现正常的分泌高峰。在注射四氧嘧啶前１２ｈ预先皮下注射消炎痛的大鼠则口服葡萄糖后的第６０ｍｉｎ血糖浓度迅速升高达到高峰,然后逐渐下降。在葡萄糖刺激后血清胰岛素浓度出现明显高峰,并具有类似正常的分泌高峰。基础血糖浓度和在口服葡萄糖后３０,６０,１２０,１８０ｍｉｎ血糖浓度及相应时相的胰岛素浓度在两组之间有显著性差异。消炎痛对正常大鼠糖耐量及胰岛素分泌没有明显的影响。本实验结果提示,消炎痛预处理可能对四氧嘧啶引起的胰岛Ｂ细胞损伤具有一定的预防作用。     

消炎痛对四嘧啶引起的大鼠糖耐量和胰岛素分泌改变的影响

本实验以糖耐量为指标,观察了消炎痛抗四氧嘧啶引起的大鼠胰岛Ｂ细胞的损伤作用。皮下注射四氧嘧啶（１５０ｍｇ／ｋｇ）的大鼠经口灌注葡萄糖（５ｇ／ｋｇ）以后,血糖浓度急剧升高并在灌胃后１８０ｍｉｎ仍继续升高。在葡萄糖刺激后血清胰岛素浓度无明显升高,未出现正常的分泌高峰。在注射四氧嘧啶前１２ｈ,预先皮下注射消炎痛的大鼠则口服葡萄糖后第６０ｍｉｎ血糖浓度迅速升高达到高峰,然后逐渐下降。在葡萄糖刺激后血清胰岛     

前列腺素E_2对四氧嘧啶引起的糖尿病大鼠胰岛β细胞的保护作用

本工作用四氧嘧啶(皮下注射)造成大鼠实验性糖尿病模型。若预先由腹腔注射剂量为10μg/kg 的前列腺素E_2(PGE_2),则可使大鼠的糖尿病发病率由75％下降到12.5％;在注射四氧嘧啶72h后,血浆葡萄糖浓度的平均值由498.0±86.6mg％下降到141.9±30.5mg％。PGE_2的这种对四氧嘧啶的细胞毒性作用的缓解具有一定的剂量依从关系。通过口服葡萄糖耐量试验观察到,经过PGE_2处理的糖尿病鼠,在注射四氧嘧啶后120h,其胰岛素分泌的功能,较未处理的糖尿病鼠得到明显恢复。组织学切片也显示,胰岛β细胞内胰岛素分泌颗粒含量在PGE_2处理组较单独四氧嘧啶处理组明显增多。因此,从机能和形态学观察结果均表明,预防性注射PGE_2能减轻四氧嘧啶对胰岛β细胞造成的急性损伤,提示PGE_2对胰岛β细胞似具有细胞保护作用。     

糖尿病大鼠口服载胰岛素纳米粒的降血糖实验

目的:利用糖尿病大鼠模型,研究载有胰岛素纳米粒的降血糖作用。方法:雄性SD大鼠18只,禁食12 h后,尾静脉一次性注射5%四氧嘧啶40 mg/kg制备大鼠糖尿病模型。超声条件下,制备含胰岛素纳米粒,纳米悬液的胰岛素浓度为2 U/ml,于4℃冷藏保存。大鼠随机分为三组,口服胰岛素组(A组)、载胰岛素纳米粒组(B组)、皮下注射胰岛素组(C组)。分别于灌胃前、灌胃后0.5,1,2,4,8,12 h取血测定血糖。结果:口服载胰岛素纳米粒后能显著降低大鼠的血糖水平,起效时间晚于皮下注射胰岛素,但作用时间长久;而口服等量普通胰岛素血糖无明显变化。表明HTCC-ALG/OREC纳米粒在体内对胰岛素具有保护作用。结论:载胰岛素纳米粒具有一定的降血糖作用和缓释效果,是具有很好应用前景的口服蛋白质给药载体。     

侧脑室注射胰高血糖素对兔血浆自由脂肪酸、血糖及胰岛素浓度的影响

胰高血糖素是一种脑-肠肽,但它在脑中的生理作用尚不清楚。本工作在家兔侧脑室埋藏慢性套管,并通过注射20μl含0.5—5μg的胰高血糖素溶液,在注射后的15、45、75、105分钟各取血样测定血糖、血浆自由脂肪酸(FFA)和胰岛素的浓度。结果发现:(1)对血糖及血浆胰岛素浓度无明显影响;(2)能引起血浆 FFA 浓度降低,且与剂量有依赖关系,在注射后的45分钟,FFA 降低最明显,以后逐渐恢复;(3)皮下注射阿托品(0.2mg/kg)或静脉注射酚妥拉明(5mg/kg)均不能消除侧脑室注射胰高血糖素降低 FFA 的作用;(4)静脉注射心得安(5mg/kg)能阻断侧脑室注射胰高血糖素的降低 FFA 的作用。这似表明脑中的胰高血糖素可能参与脂代谢的调节,并可能是通过肾上腺素β-受体起作用的。     

汉防己甲素对四氧嘧啶引致大鼠胰岛β细胞损伤的保护作用

本实验采用四氧嘧啶损伤大鼠胰岛β细胞,复制糖尿病动物模型。若预先腹腔注射汉防己甲素（１００ｍｇ／ｋｇ）则可完全预防引发的糖尿病。预防组血糖（７．６３±０．４４ｍｍｏｌ／Ｌ）明显低于对照组（２５．４６±１．２１ｍｍｏｌ／Ｌ,Ｐ＜０．００１）;血清胰岛素水平（１１．３３±１．９７μＵ／ｍｌ）高于对照组（７．１３±０．４５μＵ／ｍｌ,Ｐ＜０．０５）;血浆胰高血糖素（６６．８５±５．０７ｐｇ／ｍｌ）明显低于对照组（９０．３５±３．１５ｐｇ／ｍｌ,Ｐ＜０．０１）．口服葡萄糖耐量实验显示预防组耐糖功能较对照组明显改善,糖耐量曲线下血糖面积预防组（２９．４５±１．６３ｍｌ·ｈ／Ｌ）低于对照组（１１３．２８±５．０２ｍｍｏｌ·ｈ／Ｌ,ｐ＜０．００１）。胰岛β细胞免疫组织化学染色结果显示,预防组胰岛β细胞数目及胰岛素分泌颗粒的含量均与正常大鼠胰岛相同,无形态学改变,而对照组胰岛内β细胞免疫反应阳性产物减少甚至消失。结果表明,汉防己甲素对四氧嘧啶引起的胰岛β细胞急性损伤有保护作用。     

吉林人参低聚肽对糖尿病大鼠的降血糖作用研究

目的：研究吉林人参低聚肽（GOP）对正常大鼠和糖尿病大鼠的血糖调节作用及其机制。方法：正常大鼠降血糖实验：选取雄性SD大鼠30只,根据空腹血糖值随机分为空白对照组和GOP组,GOP组以灌胃的方式给予0.25g/kg bw的人参肽溶液、空白对照组给予等剂量的蒸馏水,连续灌胃30d,测定空腹血糖水平。糖尿病模型大鼠降血糖实验：采用高热能饲料联合小剂量四氧嘧啶建立实验性糖尿病大鼠模型,雄性SD大鼠135只,根据空腹血糖水平随机分为9组：空白对照组、糖尿病模型组（HGC）、乳清蛋白组（WPC）,0.0625、0.125、0.25、0.5、1.0、2.0 g/kg bw GOP组。GOP组以灌胃方式给予不同剂量的GOP溶液、WPC组给予0.25g/kg bw的乳清蛋白溶液、HGC和空白对照组给予等体积的蒸馏水。实验期间HGC组、WPC组和GOP各组饲喂高热能饲料,空白对照组使用基础鼠料。连续灌胃28d,HGC组、WPC组和GOP各组给予四氧嘧啶103~105mg/kg bw腹腔注射,空白对照组注射等体积生理盐水。5d后进行口服葡萄糖耐量试验（OGTT）,测定胰岛素水平、糖化血清蛋白、胆固醇等指标。结果：正常大鼠降血糖实验：空白对照组和GOP组空腹血糖水平没有显著差异。糖尿病大鼠降血糖实验：与HGC组比较,GOP 0.0625、0.125、0.25g/kg bw组和WPC组大鼠空腹胰岛素、糖化血清蛋白、总胆固醇、甘油三酯、OGTT实验0.5h血糖和血糖曲线下面积明显降低。结论：GOP对正常大鼠空腹血糖没有影响,而对高热能饲料联合小剂量四氧嘧啶诱导的糖尿病大鼠的糖脂代谢紊乱具有明显的改善作用。     

甘露寡糖及壳聚糖对四氧嘧啶致糖尿病小鼠血糖血脂的影响

目的研究甘露寡糖和壳聚糖对四氧嘧啶致实验性糖尿病小鼠血糖、血脂的影响。方法随机选取70只健康小鼠,10只为正常对照组,其余由腹腔注射四氧嘧啶(150mg/kg),建立糖尿病模型,用快速血糖仪测血糖值,血糖值>11.1mmol/L的小鼠则为造模成功小鼠,将造模成功的小鼠随机分成5组,每组各12只。分别为模型对照组,高剂量、低剂量甘露寡糖处理组,高剂量、低剂量壳聚糖处理组。高低剂量分别以400mg/kg和200mg/kg糖溶液进行灌胃,空白组和模型组灌予等体积的生理盐水。12d后测定小鼠血清中血糖(GLU)、总胆固醇(CHO)、高密度脂蛋白胆固醇(HDL-C)和甘油三酯(TG)的浓度。结果甘露寡糖和壳聚糖使糖尿病小鼠的血糖与模型对照组相比有显著的降低,CHO和TG的浓度也显著降低,HDL-C显著升高;且高剂量的甘露寡糖和壳聚糖的降血糖、血脂效果优于低剂量。     

Changes in plasma glucagon, pancreatic polypeptide and insulin during development of alloxan diabetes mellitus in dog

Changes in canine plasma glucose, immunoreactive glucagon (IRG), pancreatic polypeptide (PP) and insulin (IRI) were studied during the acute development of diabetes mellitus after iv alloxan injection. 100 mg or 75 mg/kg body weight of alloxan was injected iv and blood was taken successively till one or two days later. Plasma glucose showed four phases: first immediate and moderate decrease appeared 30 min after injection, second initial hyperglycemic phase, third hypoglycemic and fourth diabetic ones. Plasma IRI had already increased to 182 +/- 60 microU/ml 10 min after injection and again began to increase after about 6 h, peaking to 134 +/- 49 microU/ml at 18 h. Plasma IRG began increasing gradually soon after alloxan injection. The initial value was 196 +/- 26 pg/ml and it increased to 534 +/- 144 pg/ml at 4 h during the initial hyperglycemic phase, then reached a higher level through the hypoglycemic and diabetic phases. The change in plasma PP was similar to that in IRG. The initial value was 256 +/- 95 pg/ml at 12 h after injection, peaking to 840 +/- 100 pg/ml in the hypoglycemic phase. Similar blunted values were obtained following 75 mg/kg alloxan injection. Thus not only plasma IRI but also plasma IRG and PP varied greatly during the acute development of alloxan diabetes and some contribution of IRG to the initial hyperglycemic phase was suggested.     

Interactions between oxytocin, glucagon and glucose in normal and streptozotocin-induced diabetic rats

Oxytocin has been suggested to have glucoregulatory functions in rats, man and other mammals. The hyperglycemic actions of oxytocin are believed to be mediated indirectly through changes in pancreatic function. The present study examined the interaction between glucose and oxytocin in normal and streptozotocin (STZ)-induced diabetic rats, under basal conditions and after injections of oxytocin. Plasma glucose and endogenous oxytocin levels were significantly correlated in cannulated lactating rats (r = 0.44, P less than 0.01). To test the hypothesis that oxytocin was acting to elevate plasma glucose, adult male rats were injected with 10 micrograms/kg oxytocin and killed 60 min later. Oxytocin increased plasma glucose from 6.1 +/- 0.1 to 6.8 +/- 0.2 mM (P less than 0.05), and glucagon from 179 +/- 12 to 259 +/- 32 pg/ml (P less than 0.01, n = 18). There was no significant effect of oxytocin on plasma insulin, although the levels were increased by 30%. A lower dose (1 microgram/kg) of oxytocin had no significant effect on plasma glucose or glucagon. To eliminate putative local inhibitory effects of insulin on glucagon secretion, male rats were made diabetic by i.p. injection of 100 mg/kg STZ, which increased glucose to greater than 18 mM and glucagon to 249 +/- 25 pg/ml (P less than 0.05). In these rats, 10 micrograms/kg oxytocin failed to further increase plasma glucose, but caused a much greater increase in glucagon (to 828 +/- 248 pg/ml) and also increased plasma ACTH. A specific oxytocin analog, Thr4,Gly7-oxytocin, mimicked the effect of oxytocin on glucagon secretion in diabetic rats. The lower dose of oxytocin also increased glucagon levels (to 1300 +/- 250 pg/ml), but the effect was not significant. A 3 h i.v. infusion of 1 nmol/kg per h oxytocin in conscious male rats significantly increased glucagon levels by 30 min in normal and STZ-rats; levels returned to baseline by 30 min after stopping the infusion. Plasma glucose increased in the normal, but not STZ-rats. The relative magnitude of the increase in glucagon was identical for normal and diabetic rats, but the absolute levels of glucagon during the infusion were twice as high in the diabetics. To test whether hypoglycemia could elevate plasma levels of oxytocin, male rats were injected i.p. with insulin and killed from 15-180 min later. Plasma glucose levels dropped to less than 2.5 mM by 15 min. Oxytocin levels increased by 150-200% at 30 min; however, the effect was not statistically significant.(ABSTRACT TRUNCATED AT 400 WORDS)     

Impact of infection on glucose-dependent liver glucose uptake during TPN: interaction with insulin

Chronic total parenteral nutrition (TPN) markedly augments net hepatic glucose uptake (NHGU). This adaptive increase is impaired by an infection despite accompanying hyperinsulinemia. In the nonadapted state, NHGU is dependent on the prevailing glucose levels. Our aims were to determine whether the adaptation to TPN alters the glucose dependence of NHGU, whether infection impairs this dependence, and whether insulin modulates the glucose dependence of NHGU during infection. Chronically catheterized dogs received TPN for 5 days. On day 3 of TPN, dogs received either a bacterial fibrin clot to induce a nonlethal infection (INF, n = 9) or a sterile fibrin clot (Sham, n = 6). Forty-two hours after clot implantation, somatostatin was infused. In Sham, insulin and glucagon were infused to match the level seen in Sham (9 +/- 1 microU/ml and 23 +/- 4 pg/ml, respectively). In infected animals, either insulin and glucagon were infused to match the levels seen in infection (25 +/- 2 microU/ml and 101 +/- 15 pg/ml; INF-HI; n = 5) or insulin was replaced to match the lower levels seen in Sham (13 +/- 2 microU/ml), whereas glucagon was kept elevated (97 +/- 9 pg/ml; INF-LO; n = 4). Then a four-step (90 min each) hyperglycemic (120, 150, 200, or 250 mg/dl) clamp was performed. NHGU increased at each glucose step in Sham (from 3.6 +/- 0.6 to 5.4 +/- 0.7 to 8.9 +/- 0.9 to 12.1 +/- 1.1 mg.kg(-1).min(-1)); the slope of the relationship between glucose levels and NHGU (i.e., glucose dependence) was higher than that seen in nonadapted animals. Infection impaired glucose-dependent NHGU in both INF-HI (1.3 +/- 0.4 to 2.9 +/- 0.5 to 5.5 +/- 1.0 to 7.7 +/- 1.6 mg.kg(-1).min(-1)) and INF-LO (0.5 +/- 0.7 to 2.2 +/- 0.6 to 4.2 +/- 1.0 to 5.8 +/- 0.8 mg.kg(-1).min(-1)). In summary, TPN augments glucose-dependent NHGU, the presence of infection decreases glucose-dependent NHGU, and the accompanying hyperinsulinemia associated with infection does not sustain the glucose dependence of NHGU.     

In vitro effects of glycosylated insulin and glucagon in perfused liver of the rat.

Using perfused liver of the rat, the hepatic uptake of glycosylated insulin (GI) and glucagon (GG) and its effects on hepatic glucose output were investigated. Insulin and glucagon were glycosylated in ambient high glucose concentration, and GI80 or GG80 (insulin or glucagon incubated with 0.08% glucose), GI350 or GG350 (incubated with 0.35% glucose), and GI1000 or GG1000 (incubated with 1% glucose) were prepared. The liver was perfused with the medium containing 1000 microU/ml insulin and 200 pg/ml glucagon or 200 microU/ml insulin and 1000 pg/ml glucagon. The fractional uptake of insulin or glucagon by perfused liver was not significantly altered by the glycosylation. In the liver perfused with 1000 microU/ml insulin and 200 pg/ml glucagon, glucose output was not changed by the glycosylation of the hormones, while in the liver perfused with 200 microU/ml insulin and 1000 pg/ml glucagon, GI1000 reduced its biological activity, as reflected by insulin-mediated decrease in glucose output. These results suggest that in the liver insulin incubated with markedly high concentration of glucose reduces its biological activity at a physiological concentration in the presence of high concentration of glucagon.     

Glucagon chronically impairs hepatic and muscle glucose disposal

Defects in insulin secretion and/or action contribute to the hyperglycemia of stressed and diabetic patients, and we hypothesize that failure to suppress glucagon also plays a role. We examined the chronic impact of glucagon on glucose uptake in chronically catheterized conscious depancreatized dogs placed on 5 days of nutritional support (NS). For 3 days of NS, a variable intraportal infusion of insulin was given to maintain isoglycemia (approximately 120 mg/dl). On day 3 of NS, animals received a constant low infusion of insulin (0.4 mU.kg-1.min-1) and either no glucagon (CONT), basal glucagon (0.7 ng.kg-1.min-1; BasG), or elevated glucagon (2.4 ng.kg-1.min-1; HiG) for the remaining 2 days. Glucose in NS was varied to maintain isoglycemia. An additional group (HiG+I) received elevated insulin (1 mU.kg-1.min-1) to maintain glucose requirements in the presence of elevated glucagon. On day 5 of NS, hepatic substrate balance was assessed. Insulin and glucagon levels were 10+/-2, 9+/-1, 7+/-1, and 24+/-4 microU/ml, and 24+/-5, 39+/-3, 80+/-11, and 79+/-5 pg/ml, CONT, BasG, HiG, and HiG+I, respectively. Glucagon infusion decreased the glucose requirements (9.3+/-0.1, 4.6+/-1.2, 0.9+/-0.4, and 11.3+/-1.0 mg.kg-1.min-1). Glucose uptake by both hepatic (5.1+/-0.4, 1.7+/-0.9, -1.0+/-0.4, and 1.2+/-0.4 mg.kg-1.min-1) and nonhepatic (4.2+/-0.3, 2.9+/-0.7, 1.9+/-0.3, and 10.2+/-1.0 mg.kg-1.min-1) tissues decreased. Additional insulin augmented nonhepatic glucose uptake and only partially improved hepatic glucose uptake. Thus, glucagon impaired glucose uptake by hepatic and nonhepatic tissues. Compensatory hyperinsulinemia restored nonhepatic glucose uptake and partially corrected hepatic metabolism. Thus, persistent inappropriate secretion of glucagon likely contributes to the insulin resistance and glucose intolerance observed in obese and diabetic individuals.     

Stevioside induces antihyperglycaemic, insulinotropic and glucagonostatic effects in vivo: studies in the diabetic Goto-Kakizaki (GK) rats.

Extracts of leaves from the plant Stevia rebaudiana Bertoni have been used in the traditional treatment of diabetes in Paraguay and Brazil. Recently, we demonstrated a direct insulinotropic effect in isolated mouse islets and the clonal beta cell line INS-1 of the glycoside stevioside that is present in large quantity in these leaves. Type 2 diabetes is a chronic metabolic disorder that results from defects in both insulin and glucagon secretion as well as insulin action. In the present study we wanted to unravel if stevioside in vivo exerts an antihyperglycaemic effect in a nonobese animal model of type 2 diabetes. An i.v. glucose tolerance test (IVGT) was carried out with and without stevioside in the type 2 diabetic Goto-Kakizaki (GK) rat, as well as in the normal Wistar rat. Stevioside (0.2 g/kg BW) and D-glucose (2.0 g/kg BW) were administered as i.v. bolus injections in anaesthetized rats. Stevioside significantly suppressed the glucose response to the IVGT in GK rats (incremental area under the curve (IAUC): 648 +/- 50 (stevioside) vs 958 +/- 85 mM x 120 min (control); P < 0.05) and concomitantly increased the insulin response (IAUC: 51116 +/- 10967 (stevioside) vs 21548 +/- 3101 microU x 120 min (control); P < 0.05). Interestingly, the glucagon level was suppressed by stevioside during the IVGT, (total area under the curve (TAUC): 5720 +/- 922 (stevioside) vs 8713 +/- 901 pg/ml x 120 min (control); P < 0.05). In the normal Wistar rat stevioside enhanced insulin levels above basal during the IVGT (IAUC: 79913 +/- 3107 (stevioside) vs 17347 +/- 2882 microU x 120 min (control); P < 0.001), however, without altering the blood glucose response (IAUC: 416 +/- 43 (stevioside) vs 417 +/- 47 mM x 120 min (control)) or the glucagon levels (TAUC: 5493 +/- 527 (stevioside) vs 5033 +/- 264 pg/ml x 120 min (control)). In conclusion, stevioside exerts antihyperglycaemic, insulinotropic, and glucagonostatic actions in the type 2 diabetic GK rat, and may have the potential of becoming a new antidiabetic drug for use in type 2 diabetes.     

Sensitivity and responsiveness of glucose output to insulin in isolated perfused liver from dexamethasone-treated rats

To elucidate insulin action on hepatic glucose output (glycogenolysis) in the state exposed to an excess glucocorticoid, the fed rat liver was isolated and cyclically perfused with a medium containing 5 mM glucose and various concentrations of insulin. The rat was subcutaneously injected with 1 mg/kg of dexamethasone (Dex) for 7 days. Dex-treated rats showed marked increases of serum insulin and plasma glucose level compared with those in control rats. Hepatic glycogen contents in Dex group were markedly increased compared with those in control (115 +/- 5 and 28 +/- 4 mg/g, respectively). Insulin extraction rate in the perfused liver was not different between control and Dex group. Perfusate glucose level after 60 min perfusion was much higher in the Dex-treated rat liver than that of the control at 0 microU/ml insulin (34.5 +/- 2.5 vs 23.0 +/- 2.0 mM, P less than 0.01), and reduced to the nadir level (19.0 +/- 3.0 and 13.0 +/- 1.5 mM, respectively) at 100 microU/ml insulin in both groups, i.e., the decreasing rate in perfusate glucose level was not different between Dex and control group (43% and 44%, respectively). These results suggest that Dex-treatment augments hepatic glucose output, but does not affect the sensitivity and responsiveness of that to insulin.     

In vivo insulin responsiveness for glucose uptake and production at eu- and hyperglycemic levels in normal and diabetic rats.

Whole body glucose uptake (BGU) and hepatic glucose production (HGP) at maximal plasma insulin concentrations (+/- 5000 microU/ml) were determined by eu- (EC) (6 mM) and hyperglycemic (HC) (20 mM) clamps (120 min), combined with [3-3H]glucose infusion, in normal and streptozotocin-treated (65 mg/kg) 3-day diabetic, conscious rats. In normal rats, during EC, BGU was 12.4 +/- 0.4 mg/min and during HC, when urinary glucose loss was 0.54 +/- 0.09 mg/min, BGU was 25.5 +/- 1.6 mg/min. However, throughout the final 60 min of HC, glucose infusion rate (GIR) was not constant but a linear decline in time (r = -0.99) of 17%, P less than 0.0001, was observed indicating a hyperglycemia-induced desensitization process. In diabetic rats, during EC, BGU was 7.7 +/- 0.3 mg/min and during HC, BGU was 15.5 +/- 1.4 mg/min. Throughout the final 60 min of HC, GIR was constant, suggesting that the hyperglycemia-induced desensitization process was already completed. In normal and diabetic rats, HGP was similar: during EC 0.2 +/- 0.5 mg/min and 0.1 +/- 0.5 mg/min, and during HC 0.4 +/- 0.4 mg/min and 0.5 +/- 0.6 mg/min, respectively. In vitro adipocyte and muscle insulin receptor studies showed normal to increased receptor number and increased receptor autophosphorylation in diabetic compared to normal rats. In conclusion: (i) 3-day diabetic rats show, at maximal plasma insulin concentrations, insulin resistance to BGU, but not to HGP. The resistance to BGU is equally present (reduction of 38%) at eu- and hyperglycemic levels as compared to normal rats. (ii) 3-day diabetic rats reveal no defect in adipocyte and muscle insulin receptor function. These data indicate that the diabetes induced insulin resistance for BGU is at the post-receptor level and due to a decreased maximal capacity (Vmax) for glucose uptake, with no change in affinity, or Km.     

High-dose oral vitamin C partially replenishes vitamin C levels in patients with Type 2 diabetes and low vitamin C levels but does not improve endothelial dysfunction or insulin resistance

Endothelial dysfunction is a hallmark of Type 2 diabetes related to hyperglycemia and oxidative stress. Nitric oxide-dependent vasodilator actions of insulin may augment glucose disposal. Thus endothelial dysfunction may worsen insulin resistance. Intra-arterial administration of vitamin C improves endothelial dysfunction in diabetes. In the present study, we investigated effects of high-dose oral vitamin C to alter endothelial dysfunction and insulin resistance in Type 2 diabetes. Plasma vitamin C levels in 109 diabetic subjects were lower than healthy (36 +/- 2 microM) levels. Thirty-two diabetic subjects with low plasma vitamin C (<40 microM) were subsequently enrolled in a randomized, double-blind, placebo-controlled study of vitamin C (800 mg/day for 4 wk). Insulin sensitivity (determined by glucose clamp) and forearm blood flow in response to ACh, sodium nitroprusside (SNP), or insulin (determined by plethysmography) were assessed before and after 4 wk of treatment. In the placebo group (n = 17 subjects), plasma vitamin C (22 +/- 3 microM), fasting glucose (159 +/- 12 mg/dl), insulin (19 +/- 7 microU/ml), and SI(Clamp) [2.06 +/- 0.29 x 10(-4) dl x kg(-1) x min(-1)/(microU/ml)] did not change significantly after placebo treatment. In the vitamin C group (n = 15 subjects), basal plasma vitamin C (23 +/- 2 microM) increased to 48 +/- 6 microM (P < 0.01) after treatment, but this was significantly less than that expected for healthy subjects (>80 microM). No significant changes in fasting glucose (156 +/- 11 mg/dl), insulin (14 +/- 2 microU/ml), SI(Clamp) [2.71 +/- 0.46 x 10(-4) dl x kg(-1) x min(-1)/(microU/ml)], or forearm blood flow in response to ACh, SNP, or insulin were observed after vitamin C treatment. We conclude that high-dose oral vitamin C therapy, resulting in incomplete replenishment of vitamin C levels, is ineffective at improving endothelial dysfunction and insulin resistance in Type 2 diabetes.     

Infection impairs insulin-dependent hepatic glucose uptake during total parenteral nutrition

Total parenteral nutrition (TPN) markedly augments net hepatic glucose uptake (NHGU) and hepatic glycolysis in the presence of mild hyperglycemia and hyperinsulinemia. This increase is impaired by an infection. We determined whether the adaptation to TPN alters the responsiveness of the liver to insulin and whether infection impairs that response. Chronically catheterized dogs received TPN for 5 days. On day 3 of TPN, either a nonlethal hypermetabolic infection was induced (INF, n = 5) or a sham surgery was performed (SHAM, n = 5). Forty-two hours after clot implantation, somatostatin and glucagon (34 +/- 3 vs. 84 +/- 11 pg/ml in artery, SHAM vs. INF) were infused, and a three-step (120 min each) isoglycemic (approximately 120 mg/dl) hyperinsulinemic (approximately 12, 25, and 50 microU/ml) clamp was performed to simulate levels seen in normal, infected, and exogenous insulin treatment states. In SHAM, NHGU (3.5 +/- 0.2 to 4.2 +/- 0.4 to 4.6 +/- 0.5 mg x kg(-1) x min(-1)) modestly increased. In INF, NHGU was consistently lower at each insulin step (1.1 +/- 0.5 to 2.6 +/- 0.5 to 2.8 +/- 0.7 mg x kg(-1) x min(-1)). Although NHGU increased from the first to the second step in INF, it did not increase further with the highest dose of insulin. Despite increases in NHGU, net hepatic lactate release did not increase in SHAM and fell in INF. In summary, in the TPN-adapted state, liver glucose uptake is unresponsive to increases in insulin above the basal level. Although the infection-induced increase in insulin sustains NHGU, further increments in insulin enhance neither NHGU nor glycolysis.