肝脏缺血-再灌注2相损伤对胰岛β细胞分泌功能的影响

目的 研究大鼠肝脏缺血-再灌注2相损伤对胰岛β细胞分泌功能的影响.方法 36只SD大鼠随机分为假手术组(C组)和IR组,每组18只.IR组制成肝脏缺血1 h再灌注12 h的70%肝脏I/R损伤模型.每组取10只大鼠,再灌注12 h后采血,测定血糖及血胰岛素浓度并计算胰岛素分泌指数.每组另各取8只大鼠,进行高血糖钳夹试验.结果 IR组血糖水平明显高于C组[(9.02±1.37)mmol/L vs.(5.52±0.95)mmol/L](P<0.01),胰岛素浓度也显著高于C组[(116.45±10.87)mU/L vs.(73.65±22.87)mU/L](P<0.01),但IR组胰岛素分泌指数显著低于C组[(462.80±46.28) vs.(1 046.54±30.21)](P<0.01).高血糖钳夹试验显示,IR组2相胰岛素分泌量显著低于C组[(83.17±6.01)mU/L vs.(99.80±10.81)mU/L](P<0.05),葡萄槠代谢率也明显低于C组[(29.68±4.92)mg·kg-1·min-1 vs.(53.16±3.45)mg·kg-1·min-1](P<0.01),胰岛素敏感性指数显著低于C组[(30.97±8.11) vs.(64.34±7.21)](P<0.01).结论 肝脏缺血-再灌注损伤12 h后,大鼠胰岛β细胞分泌功能受损,外周组织的胰岛素敏感性明显下降.     

七氟醚预处理对肝脏缺血-再灌注损伤及PI3K/Akt信号通路的影响

目的 探讨七氟醚预处理对肝脏缺血-再灌注损伤及磷脂酰肌醇3激酶/蛋白激酶B(PI3K/Akt)信号通路的影响.方法 48只成年SD大鼠随机分为假手术组(SH组)、缺血-再灌注组(IR组)、七氟醚预处理组(SI组)和七氟醚Wortmannin组(SW组),每组12只.除SH组外,IR组、SI组和SW组建立70％肝脏缺血-再灌注模型.检测大鼠血清谷草转氨酶(AST)和谷丙转氨酶( ALT)含量,并取再灌注的肝组织用ELISA法测IL-1β浓度,用Western Blot法测定肝组织的p-PI3K、p-Akt(ser473)、Akt等表达量;用HE染色进行病理学检查,观察肝细胞损伤及坏死情况.结果 与SW组比较,SI组ALT、AST和IL-1β浓度明显降低(P＜0.05),且p-PI3K、p-Akt(ser473)表达量明显增加(P＜0.05),肝组织损伤减轻.结论 七氟醚对肝脏缺血-再灌注损伤有保护作用,可能通过激活PI3K/Akt信号通路起作用.     

肝脏缺血-再灌注损伤对大鼠肝胰岛素信号转导分子的影响

目的研究肝脏缺血-再灌注损伤(HIRI)大鼠肝细胞胰岛素信号转导过程中信号蛋白表达的改变,探讨引起HIRI后高血糖的机制。方法选用健康SD大鼠80只,随机分为对照组(C组)和缺血-再灌注组(IR组),每组40只。IR组建立HIRI大鼠模型(肝门阻断30min后再灌注2h),分别测定肝门阻断前(T1)及肝门阻断30min再灌注2h(T2)血糖(BG)、血胰岛素(Ins)的浓度。检测两组大鼠肝组织胰岛素受体β亚单位(IRβ)、胰岛素受体底物2(IRS2)及其酪氨酸磷酸化蛋白表达的改变。结果与T1比较,两组大鼠T2时BG均明显升高(P<0.01),但IR组更为明显(P<0.01)。与T1比较,IR组T2时Ins无明显变化,C组明显升高(P<0.05)。与C组比较,两组大鼠肝组织内IRβ、IRS2总蛋白表达无明显差异,但其酪氨酸磷酸化蛋白表达水平分别减少了32.2%(P<0.05)和47.7%(P<0.01)。结论HIRI导致肝胰岛素信号转导通路中IRβ、IRS2蛋白的酪氨酸磷酸化表达水平降低,从而影响葡萄糖代谢过程,这可能是HIRI后血糖升高的原因之一。     

肢体缺血预处理对大鼠肝脏缺血再灌注致心肌损伤的影响

目的 探讨单侧后肢缺血预处理对大鼠肝脏缺血再灌注致心肌损伤的影响.方法 成年雄性Wistar大鼠72只,体重200～250 g,随机分为3组(n=24),假手术组(S组)仅暴露肝门;肝脏缺血再灌注组(IR组)肝脏缺血60min后恢复灌注;后肢缺血预处理组(LIP组)阻断右侧后肢动脉、静脉和肌间侧支血流10 min后恢复灌注,30 min后建立肝脏缺血再灌注模型.于肝脏再灌注即刻、1、6 h各处死8只大鼠,测定血清脑钠素(BNP)浓度和心肌细胞膜Na+-K+-ATP酶活性,观察心肌超微结构.结果 与S组比较,IR组和LIP组心肌细胞膜Na+-K+-ATP酶活性降低,血清BNP浓度升高(P＜0.05或0.01).与IR组比较,LIP组心肌细胞膜Na+-K+-ATP酶活性升高(P＜0.05),心肌病理损伤程度减轻.结论 单侧后肢缺血预处理可减轻大鼠肝脏缺血再灌注致心肌损伤的程度.     

缺血后处理和预处理对大鼠骨骼肌缺血-再灌注损伤的作用

目的 探讨缺血后处理( IPost)和缺血预处理(IPC)对大鼠骨骼肌缺血再灌注(IR)损伤的影响.方法 将40只大鼠随机分成缺血再灌注组(A组)、缺血后处理组(B组)、缺血预处理组(C组)、缺血预处理加缺血后处理组(D组)以及对照组(E组),采用切断患肢全部皮肤、肌肉和神经,保留患肢股动、静脉的动物模型,通过夹闭和开放股动、静脉造成骨骼肌缺血再灌注损伤,通过测定骨骼肌缺血4h、再灌注1h后血清丙二醛(MDA)和骨骼肌髓过氧化物酶(MPO),以及再灌注6h后骨骼肌的坏死程度来观察缺血后处理.缺血预处理及缺血预处理加缺血后处理对大鼠骨骼肌缺血再灌注损伤的影响.结果 B组、C组和D组再灌注1 h MDA和MPO水平以及再灌注6h骨骼肌坏死程度均低于A组(P＜ 0.05),但是高于E组(P＜0.05);B组和D组再灌注1 h MDA和MPO水平以及再灌注6h骨骼肌坏死程度基本相同(P＞0.05);B组和D组再灌注1 h MDA和MPO水平低于C组(P＜0.05),但再灌注6h骨骼肌坏死程度基本相同(P＞0.05).结论 应用缺血后处理和缺血预处理对大鼠骨骼肌缺血再灌注损伤有一定的保护效果,联合应用缺血后处理和缺血预处理,对骨骼肌缺血再灌注损伤的保护作用并没有明显增强.     

还原型谷胱甘肽预处理对肝脏缺血-再灌注后糖代谢的影响

目的 观察还原型谷胱甘肽(GSH)预处理对肝脏缺血-再灌注损伤(HIRI)后糖代谢的影响.方法 78只SD大鼠随机均分为假手术组(C组)、缺血-再灌注组(IR组)和GSH预处理组(G组).IR组和G组大鼠制作HIRI模型,C组仅开腹,不阻断肝门血管.每组分别在HIRI后2、6 h各取8只大鼠检测超氧化物歧化酶(SOD)、丙二醛(MDA)、血糖和胰岛素的含量,另取5只大鼠做高血糖钳夹试验后检测胰岛素含量,并计算葡萄糖代谢率(GMR)和胰岛素敏感指数(ISI).结果 与IR组比较,C组和G组血糖、MDA含量明显降低(P<0.05),胰岛素、SOD含量明显升高(P<0.05).高血糖钳夹试验后,与IR组比较,C组和G组胰岛素含量,GMR及ISI均明显升高(P<0.05).结论 GSH预处理可改善HIRI后的高血糖,其机制可能与GSH减轻HIRI过程中的氧化还原反应有关.     

肝脏缺血再灌注后急性肺损伤的机制及丙泊酚对其的保护作用

目的 观察肝脏缺血再灌注后急性肺损伤的发病机制及丙泊酚的保护作用.方法 成年封闭群SD雄性大鼠48只,采用随机数字表法随机分为:假手术组(Sham):假手术2 h(Sham2)组;假手术6 h(Sham6)组;缺血再灌注组(IR):缺血再灌注2 h(IR2)组;缺血再灌注6 h(IR6)组及丙泊酚组(P):丙泊酚2 h...     

大鼠肝脏缺血再灌注损伤早期载脂蛋白M的表达

目的 探讨大鼠肝缺血再灌注损伤早期肝内载脂蛋白M mRNA(apoM mRNA)及血浆apoM的表达。方法 建立大鼠肝脏缺血再灌注损伤模型。健康雄性SD大鼠40只随机分成5组，每组8只：假手术组(对照组)；IR1组(灌注0．5h)；[R2组(灌注1．0h)；IR3组(灌注2．0h)；[R4组(灌注3．0h)。缺血再灌注组的缺血时间统一为1．0h。检测血浆谷丙转氨酶水平(ALT)、肝组织病理变化、血浆apoM蛋白及肝组织apoM mRNA。结果 血浆ALT的水平随着灌注时间的延长而升高，肝组织损伤随着灌注时间的延长而逐渐加重。肝组织apoM mRNA的表达则先有一过性下降(灌注0．5h组)，此后随着灌注时间的延长其表达明显增强。血浆apoM蛋白有相同的变化趋势，但其表达在灌注2．0h才有上升。结论 在肝缺血再灌注损伤过程中，肝脏apoM mRNA的表达和血浆蛋白水平有迅速、明显的变化，提示apoM可能具有急性时相反应蛋白的特性。     

缺血预处理对大鼠肝脏缺血再灌注损伤后细胞凋亡的影响

目的:研究缺血预处理(IP)对大鼠肝脏缺血再灌注(IR)损伤后细胞凋亡的影响。方法 :健康成年雄性SD大鼠随机分为3组(每组5只)。SO组(假手术组):只麻醉开腹,不阻断肝脏血流;IR组:采用Pringle法大鼠肝脏缺血30m in再灌注3 h;IP组:在IR前先阻断肝门血流10 m in,然后开放血流10m in,其余步骤同IR组。各组均在术后3h后取组织进行检测。流式细胞术检测细胞凋亡;W-B法检测凋亡相关蛋白B cl-2、C aspase-3;生化分析仪检测A ST、A LT的活性。结果:与单纯IR相比,IP预处理明显降低了再灌注3 h所致肝组织细胞凋亡率(P0.05);同时增加肝组织抗凋亡蛋白B cl-2含量,降低凋亡蛋白C aspase-3的表达(P0.05);降低血中A ST、A LT的活性(P0.05)。结论:IP处理减少肝脏IR期间的细胞凋亡比率,其主要机制可能通过增加抗凋亡蛋白B cl-2表达,降低凋亡蛋白C aspase-3表达来实现,同时伴随血清A ST、A LT减少,从而减轻IR术后肝功能的损害。     

大鼠肝脏缺血-再灌注损伤时齐墩果酸对氧自由基的影响

目的 探讨齐墩果酸(OA)对大鼠肝脏缺血-再灌注损伤时氧自由基的影响.方法 128只雄性SD大鼠随机分为假手术组(SH组)、缺血-再灌注组(IR组)、羧甲基纤维素钠(CMC-Na组)和OA组.建立70%肝脏缺血-再灌注模型,测定肝脏缺血60 min再灌注0、3、6、12 h后血清ALT活性和肝组织丙二醛(MDA)水平、超氧化物歧化酶(SOD)活性、谷胱甘肽(GSH)水平.结果 再灌注3、6、12 h,IR组、CMC-Na组、OA组血清ALT活性、肝组织MDA水平分别显著高于SH组(P<0.05),肝组织SOD活性、GSH水平分别明显低于SH组(P<0.05);OA组ALT活性、MDA水平分别较IR组和CMC-Na组明显降低(P<0.05),SOD活性和GSH水平分别较IR组和CMC-Na组显著升高(P<0.05).结论 OA对肝脏缺血-再灌注损伤具有一定保护作用,其抗肝脏缺血-再灌注损伤作用与抑制自由基的生成和释放有关.     

Hepatic Ischemia-Reperfusion Induces Insulin Resistance via Down-Regulation During the Early Steps in Insulin Signaling in Rats

Background

The effects of hepatic ischemia-reperfusion (I/R) on insulin signaling remain unclear. We observed changes in insulin secretion and signal protein expression during the early steps in insulin signaling after hepatic I/R in rats.

Materials and Methods

Eighty healthy Wistar rats were randomly divided into an I/R group and a control (C) group. After we exposed the hepatic hilum, ischemia was induced by clamping the hepatic artery and portal vein for 30 minutes and then the liver was reperfused for 2 hours in the I/R group; a show procedure was done in the C group. Blood samples were obtained after exposure of the hepatic hilum (T1) and 2 hours after reperfusion in the I/R group (T2) and 2.5 hours after T1 in the C group (T2). We measured glucose and insulin plasma concentrations. We determined the expressions of insulin signaling proteins, including insulin receptor (IR) β unit (IR β), IR substrate 1 (IRS-1), IRS-2, and P85 in phosphatidylinositol 3-kinase (PI3K) and tyrosine phosphorylation of these proteins in liver and skeletal muscle.

Results

Plasma glucose concentrations increased in both groups at T2 (P < .01) and were higher in the I/R group (P < .01). Insulin concentrations in the I/R group did not change significantly at T2. Insulin concentrations at T2 were higher than those at T1 in the C group (P < .05). Expressions of insulin signal proteins showed no significant difference between the 2 groups; however, tyrosine phosphorylation of IR β, IRS-1, IRS-2, and the interactions between IRS-1 in skeletal muscle or IRS-2 in liver and PI3K were significantly lower in the I/R group than the C group.

Conclusion

Hepatic I/R inhibited insulin secretion and induced insulin resistance via down-regulation during the early steps in insulin signaling in rats.     

参附注射液对兔体外循环时胰岛素抵抗的影响

目的 探讨参附注射液SFI对兔CPB时胰岛素抵抗的影响.方法 健康成年新西兰大白兔30只,雌雄不拘,体重2.2～2.5 kg,随机分为3组(n=10),假手术组(S组)和CPB组腹腔注射等容量生理盐水,SFI组于CPB前2 d、1 d及麻醉诱导前30 min时腹腔注射SFI 10 ml/kg.于麻醉诱导后5 min(T_1)、主动脉阻断即刻(T_2)、主动脉开放5 min(T_3)、主动脉开放35 min(T_4)和主动脉开放75 min (T_5)时采集动脉血样,测定血糖及胰岛素水平,并计算胰岛素抵抗指数(HOMA-IR).于CPB 150 min时取右后肢股四头肌组织,测定骨骼肌胰岛素受体底物-1(IRS-1)、磷脂酰肌醇3激酶p85亚单位(P13Kp85)、葡萄糖转运蛋白(GLUT)4的表达水平.结果 与T_1时比较,3组T_(2～5)时血糖、胰岛素水平及HOMA-IR均升高(P<0.05);与S组比较,CPB组和SFI组T_(2～5)时血糖、胰岛素水平及HOMA-IR均升高,P13Kp85及GLUT4表达下调(P<0.05);与CPB组比较,SFI组T_(2～5)时血糖水平及HOMA-IR降低,胰岛素水平升高,P13Kp85及GLUT4表达上调(P<0.05).结论 SFI可改善CPB诱导的兔胰岛素抵抗,其机制可能与上调骨骼肌胰岛素信号转导分子的表达有关.     

Differential effects of interleukin-6 and -10 on skeletal muscle and liver insulin action in vivo

The circulating level of the inflammatory cytokine interleukin (IL)-6 is elevated in various insulin-resistant states including type 2 diabetes, obesity, cancer, and HIV-associated lipodystrophy. To determine the role of IL-6 in the development of insulin resistance, we examined the effects of IL-6 treatment on whole-body insulin action and glucose metabolism in vivo during hyperinsulinemic-euglycemic clamps in awake mice. Pretreatment of IL-6 blunted insulin's ability to suppress hepatic glucose production and insulin-stimulated insulin receptor substrate (IRS)-2-associated phosphatidylinositol (PI) 3-kinase activity in liver. Acute IL-6 treatment also reduced insulin-stimulated glucose uptake in skeletal muscle, and this was associated with defects in insulin-stimulated IRS-1-associated PI 3-kinase activity and increases in fatty acyl-CoA levels in skeletal muscle. In contrast, we found that co-treatment of IL-10, a predominantly anti-inflammatory cytokine, prevented IL-6-induced defects in hepatic insulin action and signaling activity. Additionally, IL-10 co-treatment protected skeletal muscle from IL-6 and lipid-induced defects in insulin action and signaling activity, and these effects were associated with decreases in intramuscular fatty acyl-CoA levels. This is the first study to demonstrate that inflammatory cytokines IL-6 and IL-10 alter hepatic and skeletal muscle insulin action in vivo, and the mechanism may involve cytokine-induced alteration in intracellular fat contents. These findings implicate an important role of inflammatory cytokines in the pathogenesis of insulin resistance.     

Characterization of signal transduction and glucose transport in skeletal muscle from type 2 diabetic patients

We characterized metabolic and mitogenic signaling pathways in isolated skeletal muscle from well-matched type 2 diabetic and control subjects. Time course studies of the insulin receptor, insulin receptor substrate (IRS)-1/2, and phosphatidylinositol (PI) 3-kinase revealed that signal transduction through this pathway was engaged between 4 and 40 min. Insulin-stimulated (0.6-60 nmol/l) tyrosine phosphorylation of the insulin receptor beta-subunit, mitogen-activated protein (MAP) kinase phosphorylation, and glycogen synthase activity were not altered in type 2 diabetic subjects. In contrast, insulin-stimulated tyrosine phosphorylation of IRS-1 and anti-phosphotyrosine-associated PI 3-kinase activity were reduced 40-55% in type 2 diabetic subjects at high insulin concentrations (2.4 and 60 nmol/l, respectively). Impaired glucose transport activity was noted at all insulin concentrations (0.6-60 nmol/l). Aberrant protein expression cannot account for these insulin-signaling defects because expression of insulin receptor, IRS-1, IRS-2, MAP kinase, or glycogen synthase was similar between type 2 diabetic and control subjects. In skeletal muscle from type 2 diabetic subjects, IRS-1 phosphorylation, PI 3-kinase activity, and glucose transport activity were impaired, whereas insulin receptor tyrosine phosphorylation, MAP kinase phosphorylation, and glycogen synthase activity were normal. Impaired insulin signal transduction in skeletal muscle from type 2 diabetic patients may partly account for reduced insulin-stimulated glucose transport; however, additional defects are likely to play a role.     

Evidence for an intrahepatic contribution to the waning effect of glucagon on glucose production in the conscious dog

We previously showed that infusion of glucagon at four times the basal rate into conscious dogs given somatostatin and basal replacement amounts of insulin caused hyperglycemia (217 15 mg/dl) for at least 3 h and an initial increment in hepatic glucose production of 5.5 0.8 mg/kg . min. After 3 h, however, the effect of hyperglucagonemia on glucose production had declined by 85%. The aim of the present study was to determine the importance of hyperglycemia in the "downregulation" of the action of glucagon. Six overnight-fasted conscious dogs were given somatostatin (0.8 microgram/kg . min) plus basal intraportal replacement amounts of insulin (263 microunits/kg . min) and glucagon (0.65 ng/kg . min). Hyperglycemia (276 12 md/dl) was established after 2 h by the infusion of exogenous glucose. The glucagon infusion rate was then increased fourfold 1 h later, so that the plasma glucagon level rose from 95 16 to 227 35 pg/ml. The glucose concentration was maintained at a fixed value despite the increase in glucagon by decreasing the glucose infusion rate by an amount equal to the increase in endogenous glucose production induced by the hormone. Glucose production was measured using a primed infusion of 3H-glucose. With the insulin (11 2 microunits/ml) and glucose levels fixed, the elevation in glucagon caused an initial increment of 5.1 0.7 mg/kg . min in glucose production which was followed by a fall of only 2.5 0.4 mg/kg . min (50%) over the next 3 hr. Thus, when the plasma glucagon level is raised fourfold under conditions in which insulin mobilization cannot occur, the effect of hyperglucagonemia on glucose production will be partially offset by the resulting hyperglycemia and partly inhibited by an hepatic factor(s).     

Insulin signal transduction in skeletal muscle from glucose-intolerant relatives of type 2 diabetic patients [corrected].

To determine whether defects in the insulin signal transduction cascade are present in skeletal muscle from prediabetic individuals, we excised biopsies from eight glucose-intolerant male first-degree relatives of patients with type 2 diabetes (IGT relatives) and nine matched control subjects before and during a euglycemic-hyperinsulinemic clamp. IGT relatives were insulin-resistant in oxidative and nonoxidative pathways for glucose metabolism. In vivo insulin infusion increased skeletal muscle insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation (P = 0.01) and phosphatidylinositide 3-kinase (PI 3-kinase) activity (phosphotyrosine and IRS-1 associated) in control subjects (P < 0.02) but not in IGT relatives (NS). The incremental increase in insulin action on IRS-1 tyrosine phosphorylation was lower in IGT relatives versus control subjects (P < 0.05). The incremental defects in signal transduction noted for IRS-1 and PI 3-kinase may be attributed to elevated basal phosphorylation/activity of these parameters, because absolute phosphorylation/activity under insulin-stimulated conditions was similar between IGT relatives and control subjects. Insulin increased Akt serine phosphorylation in control subjects and IGT relatives, with a tendency for reduced phosphorylation in IGT relatives (P = 0.12). In conclusion, aberrant phosphorylation/activity of IRS-1, PI 3-kinase, and Akt is observed in skeletal muscle from relatives of patients with type 2 diabetes with IGT. However, the elevated basal activity of these signaling intermediates and the lack of a strong correlation between these parameters to glucose metabolism suggests that other defects of insulin signal transduction and/or downstream components of glucose metabolism may play a greater role in the development of insulin resistance in skeletal muscle from relatives of patients with type 2 diabetes.     

Insulin sensitively controls the glucagon response to mild hypoglycemia in the dog

In the present study, we examined how the arterial insulin level alters the alpha-cell response to a fall in plasma glucose in the conscious overnight fasted dog. Each study consisted of an equilibration (-140 to -40 min), a control (-40 to 0 min), and a test period (0 to 180 min), during which BAY R 3401 (10 mg/kg), a glycogen phosphorylase inhibitor, was administered orally to decrease glucose output in each of four groups (n = 5). In group 1, saline was infused. In group 2, insulin was infused peripherally (3.6 pmol. kg(- 1). min(-1)), and the arterial plasma glucose level was clamped to the level seen in group 1. In group 3, saline was infused, and euglycemia was maintained. In group 4, insulin (3.6 pmol. kg(-1). min(-1)) was given, and euglycemia was maintained by glucose infusion. In group 1, drug administration decreased the arterial plasma glucose level (mmol/l) from 5.8 +/- 0.2 (basal) to 5.2 +/- 0.3 and 4.4 +/- 0.3 by 30 and 90 min, respectively (P < 0.01). Arterial plasma insulin levels (pmol/l) and the hepatic portal-arterial difference in plasma insulin (pmol/l) decreased (P < 0.01) from 78 +/- 18 and 90 +/- 24 to 24 +/- 6 and 12 +/- 6 over the first 30 min of the test period. The arterial glucagon levels (ng/l) and the hepatic portal-arterial difference in plasma glucagon (ng/l) rose from 43 +/- 5 and 5 +/- 2 to 51 +/- 5 and 10 +/- 5 by 30 min (P < 0.05) and to 79 +/- 16 and 31 +/- 15 (P < 0.05) by 90 min, respectively. In group 2, in response to insulin infusion, arterial insulin (pmol/l) was elevated from 48 +/- 6 to 132 +/- 6 to an average of 156 +/- 6. The hepatic portal-arterial difference in plasma insulin was eliminated, indicating a complete inhibition of endogenous insulin release. The arterial glucagon level (ng/l) and the hepatic portal-arterial difference in plasma glucagon (ng/l) did not rise significantly (40 +/- 5 and 7 +/- 4 at basal, 44 +/- 4 and 9 +/- 4 at 90 min, and 44 +/- 8 and 15 +/- 7 at 180 min). In group 3, when euglycemia was maintained, the insulin and glucagon levels and the hepatic portal-arterial difference remained constant. In group 4, the arterial plasma glucose level remained basal (5.9 +/- 1.1 mmol/l) throughout, whereas insulin infusion increased the arterial insulin level to an average of 138 +/- 6 pmol/l. The hepatic portal-arterial difference in plasma insulin was again eliminated. Arterial glucagon level (ng/l) and the hepatic portal-arterial difference in plasma glucagon (ng/l) did not change significantly (43 +/- 2 and 9 +/- 2 at basal, 39 +/- 3 and 9 +/- 2 at 90 min, and 37 +/- 3 and 7 +/- 2 at 180 min). Thus, a difference of approximately 120 pmol/l in arterial insulin completely abolished the response of the alpha-cell to mild hypoglycemia.     

The IR1152 mutant insulin receptor selectively impairs insulin action in skeletal muscle but not in liver

In patients harboring the IR1152 mutant insulin receptor, hepatic glucose production was normally suppressed by insulin. Hepatocytes without the insulin receptor gene and expressing IR1152 (Hep(MUT)) also showed normal insulin suppression of glucose production and full insulin response of glycogen synthase. In contrast, expression of the IR1152 mutant in skeletal muscle maximally increased glucose uptake and storage, preventing further insulin stimulation. IRS-1 phosphorylation was normally stimulated by insulin in both intact Hep(MUT) and L6 skeletal muscle cells expressing the IR1152 mutant (L6(MUT)). At variance, IRS-2 phosphorylation exhibited high basal levels with no further insulin-dependent increase in L6(MUT) but almost normal phosphorylation, both basal and insulin-stimulated, in the Hep(MUT) cells. In vitro, IR1152 mutant preparations from both the L6(MUT) and the Hep(MUT) cells exhibited increased basal and no insulin-stimulated phosphorylation of IRS-2 immobilized from either muscle or liver cells. IR1152 internalization in liver and muscle cells closely paralleled the ability of this mutant to phosphorylate IRS-2 in vivo in these cells. Block of receptor internalization (wild-type and mutant) in the liver and muscle cells also inhibited IRS-2, but not IRS-1, phosphorylation. Thus, the mechanisms controlling insulin receptor internalization differ in liver and skeletal muscle cells and may enable IR1152 to control glucose metabolism selectively in liver. In both cell types, receptor internalization seems necessary for IRS-2 but not IRS-1 phosphorylation.     

Immunoneutralization of endogenous glucagon reduces hepatic glucose output and improves long-term glycemic control in diabetic ob/ob mice

In type 2 diabetes, glucagon levels are elevated in relation to the prevailing insulin and glucose levels. The relative hyperglucagonemia is linked to increased hepatic glucose output (HGO) and hyperglycemia. Antagonizing the effects of glucagon is therefore considered an attractive target for treatment of type 2 diabetes. In the current study, effects of eliminating glucagon signaling with a glucagon monoclonal antibody (mAb) were investigated in the diabetic ob/ob mouse. Acute effects of inhibiting glucagon action were studied by an oral glucose tolerance test (OGTT) and by measurement of HGO. In addition, the effects of subchronic (5 and 14 days) glucagon mAb treatment on plasma glucose, insulin, triglycerides, and HbA1c (A1C) levels were investigated. Glucagon mAb treatment reduced the area under the curve for glucose after an OGTT, reduced HGO, and increased the rate of hepatic glycogen synthesis. Glucagon mAb treatment for 5 days lowered plasma glucose and triglyceride levels, whereas 14 days of glucagon mAb treatment reduced A1C. In conclusion, acute and subchronic neutralization of endogenous glucagon improves glycemic control, thus supporting the contention that glucagon antagonism may represent a beneficial treatment of diabetes.     

Glucosamine infusion in rats rapidly impairs insulin stimulation of phosphoinositide 3-kinase but does not alter activation of Akt/protein kinase B in skeletal muscle.

Glucosamine, a metabolite of glucose via the hexosamine biosynthetic pathway, potently induces insulin resistance in skeletal muscle by impairing insulin-induced GLUT4 translocation to the plasma membrane. Activation of phosphoinositide (PI) 3-kinase is necessary for insulin-stimulated GLUT4 translocation, and the serine/threonine kinase Akt/protein kinase B (PKB) is a downstream mediator of some actions of PI 3-kinase. To determine whether glucosamine-induced insulin resistance could be due to impaired signaling, we measured insulin receptor substrate (IRS)-1 and insulin receptor tyrosine phosphorylation; PI 3-kinase activity associated with IRS-1, IRS-2, and phosphotyrosine; and Akt activity and phosphorylation in skeletal muscle of rats infused for 2 h with glucosamine (6.0 mg x kg(-1) x min(-1)) or saline. Euglycemic-hyperinsulinemic clamp studies (12 mU x kg(-1) x min(-1) insulin) in awake rats showed that glucosamine infusion resulted in rapid induction of insulin resistance, with a 33% decrease in glucose infusion rate (P < 0.01). Tissues were harvested after saline alone (basal), 1 min after an insulin bolus (10 U/kg), or after 2 h of insulin clamp in saline- and glucosamine-infused rats. After 1 min of insulin stimulation, phosphorylation of IRS-1 and insulin receptor increased 6- to 8-fold in saline-infused rats and 7- to 10-fold in glucosamine-infused rats. In saline-infused rats, 1 min of insulin stimulation increased PI 3-kinase activity associated with IRS-1, IRS-2, or phosphotyrosine 7.6-, 6.4-, and 10-fold, respectively. In glucosamine-infused rats treated for 1 min with insulin, PI 3-kinase activity associated with IRS-1 was reduced 28% (P < 0.01) and that associated with phosphotyrosine was reduced 43% (P < 0.01). Insulin for 1 min stimulated Akt/PKB activity approximately 5-fold in both saline- and glucosamine-infused rats; insulin-induced hyperphosphorylation of Akt/PKB was not different between groups. Glucosamine infusion alone had no effect on tyrosine phosphorylation of the insulin receptor or IRS-1 or on stimulation of PI 3-kinase or Akt/PKB activity. However, 2 h of insulin clamp reduced PI 3-kinase activity associated with IRS-1, IRS-2, or phosphotyrosine to <30% of that seen with 1 min of insulin. No effect of glucosamine was seen on these signaling events when compared with 2 h of insulin clamp without glucosamine. Our data show that 1) glucosamine infusion in rats is associated with an impairment in the early activation of PI 3-kinase by insulin in skeletal muscle, 2) this insulin-resistant state does not involve alterations in the activation of Akt/PKB, and 3) prolonged insulin infusion under clamp conditions results in a blunting of the PI 3-kinase response to insulin.