Impaired central insulin response in aged Wistar rats: role of adiposity

Insulin, like leptin, is considered as a lipostatic signal acting at a central level. Aging and age-associated adiposity have been related to the development of leptin resistance in Wistar rats. In the present article, hypothalamic insulin response during aging has been studied in Wistar rats. Thus, the effects of intracerebroventricular infusion of insulin during a week on food intake and body weight as well as insulin signal transduction after acute intracerebroventricular insulin administration have been studied in 3-, 8-, and 24-month-old rats. To explore the possible role of age-associated adiposity, these experiments were also performed in 8- and 24-month-old rats after 3 months of food restriction to reduce visceral adiposity index to values below those of young animals. Intracerebroventricular administration of insulin during a week was more efficient at reducing food intake and body weight in 3-month-old rats than in 8- and 24-month-old rats. Hypothalamic insulin-stimulated insulin receptor, GSK3, AKT, and p70S6K phosphorylation decreased with aging. Insulin receptor and IRS-2 phosphoserine was increased in 24-month-old rats. Food restriction improved both insulin responsiveness and insulin signaling. These data suggest that Wistar rats develop hypothalamic insulin resistance with aging. This can be explained by alterations of the signal transduction pathway. The fact that food restriction improves central insulin response and signal transduction points to the age-associated adiposity as a key player in the development of central insulin resistance.     

肾上腺髓质素对正常Wistar大鼠胰岛素敏感性的影响

用高胰岛素正常血糖钳夹试验,联合放射性同位素稀释示踪技术观察肾上腺髓质素(AM)对正常Wistar大鼠胰岛素敏感性的影响。输入生理盐水及0.05、0.2、1μg·kg-1·min-1等不同剂量的AM,测定葡萄糖利用率(GDR)、肝脏葡萄糖输出率(HGO)。AM可使正常Wistar大鼠胰岛素刺激下的GDR值下降,并有剂量依赖趋势,尤以1μg·kg-1·min-1最明显(下降51%),可能还有增加HGO的作用,提示较高浓度的AM可导致以外周为主的胰岛素抵抗的发生。     

短期能量限制对正常大鼠胰岛素敏感性的影响

目的探讨短期能量限制（CR）对正常大鼠胰岛素敏感性的影响及其机制。方法将24只F344/NSIc系雄性大鼠随机分为对照组（AL组）和能量限制组（CR组）各12只。AL组自由摄入食物及水,CR组限制食物摄入（不禁水）8周（饲料总摄入量为对照组的64%）。采用高胰岛素—正常血糖钳夹试验测定两组葡萄糖输注率（GIR）判断其胰岛素敏感性（GIR越高,胰岛素敏感性越高）;比较两组体质量增加及内脏脂肪重量;Western blot法检测骨骼肌葡萄糖转运体4（Glu T4）、蛋白激酶B底物蛋白160（AS160）及磷酸化AS160（p-AS160）蛋白表达。结果CR组GIR明显高于对照组,体质量及内脏脂肪重量明显低于对照组;两组Glu T4、AS160及p-AS160蛋白表达无显著差异。结论短期CR可提高大鼠正常状态下的胰岛素敏感性,其机制可能与AS160上游的胰岛素信号转导蛋白有关。     

不同脂肪酸饮食对Wistar大鼠胰岛素敏感性的影响

目的 探讨饱和脂肪酸(SFA)、单不饱和脂肪酸(MUFA)、多不饱和脂肪酸(PUFA)饮食对大鼠胰岛素敏感性的影响.方法 48只雄性Wistar大鼠随机分为正常对照组、SFA组、MUFA组、PUFA组.正常对照组给基础饲料(脂肪占10.3%);SFA组饲料在基础饲料中添加15%猪油;MUFA组饲料在基础饲料中添加15%茶油;PUFA组饲料在基础饲料中添加15%豆油(脂肪占35.4%).8 w后4组各随机选8只大鼠行高胰岛素-正葡萄糖钳夹实验,同时留取空腹血清测定血脂、胰岛素等指标.结果 实验第8周末,与其他3组相比,正常对照组大鼠进食量有所增加,差异有统计学意义(P>0.05).除外进食量的影响,与SFA组相比,正常对照组、MUFA组、PUFA组血清TC、TG降低,差异有统计学意义(P<0.05),而正常对照组、MUFA、PUFA三组间无统计学意义(P>0.05).与正常对照组、MUFA组相比,SFA、PUFA组FINS、FPG升高,差异有统计学意义(P<0.05),GIR明显下降,差异有统计学意义(P<0.05),但该两组间无统计学差异(P>0.05).与正常对照组相比,MUFA组血清FINS、FPG有升高趋势,差异无统计学意义(P>0.05),GIR下降,差异有统计学意义(P<0.05). 结论 MUFA饮食较PUFA、SFA饮食可以改善胰岛素敏感性.     

多氯联苯118对大鼠胰岛素敏感性影响的研究

目的探讨多氯联苯（polychlorinated biphenyl,PCB）118对大鼠胰岛素敏感性的影响。方法将40只清洁级成年雄性Wistar大鼠[体重（200±10）g]按随机数字表法分为4组,每组10只,除正常对照组外,其余3组给予不同剂量PCB118：低、中、高剂量组分别为10、100、1000μg·kg^-1·d^-1,每周腹腔注射5d,造模13周后行腹腔葡萄糖耐量试验（IPGTT）,计算糖负荷后30min胰岛素增值与血糖增值比值（△I30／△G30）、葡萄糖、胰岛素曲线下面积（AUCg、AUCi）、AUCi／AUCg及稳态模型胰岛素抵抗指数（HOMA—IR）。采用单因素方差分析进行多组间均数比较。结果低、中、高剂量组空腹胰岛素水平[（19．0±7．1）、（18．5±3．1）、（22．1±1．2）mU／L]、30min胰岛素[（55．0±1．9）、（55．0±2．4）、（72．3±1．0）mU／L]及30min血糖水平[（22．32±2．44）、（19．87±1．89）、（21．90±2．88）mmol／L]明显高于对照组[（10．05±3．59）、（25．68±1．27）mU／L、（17．08±1．35）mmol／L],差异有统计学意义（F值分别为3．622、8．798、7．024,均P〈0．05）;高剂量组60、120min胰岛素水平高于对照组[60min（46．3±1．2）比（18．1±1．1）mU／L,t=3．287,P〈0．05;120min（39．5±1．3）比（24．5±9．4）mU／L,t=2．435,P〈0．05],各剂量组△I30／AGmAUCi、AUCi／AUCg明显高于对照组（F值分别为15．548、7．130、5．509,均P〈0．05）,低、中、高剂量组HOMA—IR亦明显高于对照组（1．26±0．42、1．35±0．22、1．52±0．47比0．65±0．37,F=6．937,P〈0．05）,上述指标在各剂量组问比较差异无统计学意义（均P〉0．05）。结论低剂量PCB118持续暴露可能引起大鼠胰岛素敏感性降低。     

Effects of food restriction on aging: separation of food intake and adiposity.

Restricted feeding of rodents increases longevity, but its mechanism of action is not understood. We studied the effects of life-long food restriction in genetically obese and normal mice of the same inbred strain in order to distinguish whether the reduction in food intake or the reduction in adiposity (percentage of fatty tissue) was the critical component in retarding the aging process. This was possible because food-restricted obese (ob/ob) mice maintained a high degree of adiposity. In addition to determining longevities, changes with age were measured in collagen, immune responses, and renal function. Genetically obese female mice highly congenic with the C57BL/6J inbred strain had substantially reduced longevities and increased rates of aging in tail tendon collagen and thymus-dependent immune responses, but not in urine-concentrating abilities. When their weight was held in a normal range by feeding restricted amounts, longevities were extended almost 50%, although these food-restricted ob/ob mice still had high levels of adiposity, with fat composing about half of their body weights. Their maximum longevities exceeded those of normal C57BL/6J mice and were similar to longevities of equally food-restricted normal mice that were much leaner. Food restricted ob/ob mice had greatly retarded rates of collagen aging, but the rapid losses with age in splenic immune responses were not mitigated. Thus, the extension of life-span by food restriction was inversely related to food consumption and corresponded to the aging rate of collagen. These results suggest that aging is a combination of independent processes; they show that reduced food consumption, not reduced adiposity, is the important component in extending longevity of genetically obese mice.     

Effect of age and caloric restriction on insulin receptor binding and glucose transporter levels in aging rats

We report on the effect of age and chronic caloric restriction (CR) on insulin binding and glucose transporter content in both diaphragm and heart muscle membrane of young (11 months), mid-age (17 months), and old (29 month) ad libitum fed and CR Brown-Norway rats. The control animals received rat chow ad lib and CR animals were allowed 60% of ad libitum food. The CR regimen was initiated at four months of age and the animals were maintained on their respective diets until necropsy. There was no effect of age on insulin binding for either ad libitum or CR animals at each age evaluated. Caloric restriction significantly lowered insulin levels at each age studied when compared to the ad libitum-fed rats. However, CR animals were noted to have increased insulin binding (p < 0.001) compared to ad libitum-fed animals at each age for diaphragm muscle. For the heart, there appeared to be a decreased binding, particularly at higher insulin concentrations, in CR-fed animals. There was no net change in Glut-1 or Glut-4 levels for heart muscle membrane, or Glut-4 levels for diaphragm muscle membrane between ad libitum or CR animals. This data indicates that caloric restriction may have tissue-specific effects for insulin receptor binding, and that the improved insulin sensitivity in CR states is not a result of altered glucose transporter protein content.     

Effects of moderate dietary restriction and age on blood parameters and metabolic enzymes in Lobund-Wistar rats

The effects of moderate dietary restriction (DR) on certain blood parameters and metabolic enzymes were studied in 80 male Lobund-Wistar rats at 6, 12, 18, 24 and 30 months of age. Two groups of rats were fed ad libitum (AL) or restricted (DR) to 12 g per day from weaning. Adult DR rats received 30% less diet per day when compared to adult rats in AL group. Blood glycohemoglobin levels increased significantly with age in AL rats, but not in those of the DR group. Hematocrit showed a significant decrease at 24 and 30 months in both groups. Serum glucose levels in rats were not affected by either diet or age. Five enzymes in the liver cytosolic fractions were determined. Activities of pyruvate kinase (PK) and lactate dehydrogenase (LDH) were significantly lower in the DR group than in the AL group at each age. Activities of glutamate-pyruvate transaminase (GPT), glutamate-oxaloacetate transaminase (GOT) and malate dehydrogenase (MDH) were significantly higher in the DR group than in the AL group. The results suggest that moderate DR decreased the glycolytic pathway and appears to stimulate amino acid metabolism and increase gluconeogenesis.     

西洛他唑对OLETF大鼠胰岛素敏感性的影响

目的　探讨西洛他唑对自发 2型糖尿病的动物模型OLETF大鼠胰岛素敏感性的影响。　方法　将雄性OLETF大鼠在 32周龄时根据体重及胰岛素耐量试验中 5 0min血糖下降百分率随机分成三组 :正常喂养组 ,罗格列酮治疗组及西洛他唑治疗组 ,每组 7只鼠。测给药 2 9d后的血脂水平 ;给药 38d后测空腹血糖 ,以正常血糖高胰岛素钳夹技术对以上各组进行胰岛素敏感性评价。　结果　西洛他唑组血甘油三酯水平 ( 1.95± 0 .19mmol/L)较对照组 ( 3.11± 0 .32mmol L)降低 (P <0 .0 1) ;胆固醇 ( 1.32± 0 .17mmol/L)较对照组 ( 2 .2 6± 0 .17mmol/L)降低 (P <0 .0 1) ;游离脂肪酸 ( 0 .46± 0 .11mmol/L)较对照组 ( 1.5 3± 0 .35mmol/L)降低 (P <0 .0 5 ) ;葡萄糖输注速率 ( 11.0 4±1.12mg·kg- 1 ·min- 1 )较对照组 ( 7.33± 1.12mg·kg- 1 ·min- 1 )增加 (P <0 .0 1) ;空腹血糖 ( 6 .1± 0 .7mmol/L)较对照组 ( 7.87± 1.2 3mmol/L)有所下降 ,但差异无显著意义 (P >0 .0 5 )。　结论　西洛他唑能改善OLETF大鼠的胰岛素敏感性。     

增龄对Wistar大鼠胰岛b细胞胰岛素受体的影响

目的观察增龄对大鼠胰岛β细胞胰岛素受体的影响,探讨老年糖耐量受损的机制。方法将Wistar大鼠30只分为青年组（15只）和老年组（15只）,观察空腹血糖、空腹胰岛素、血清游离脂肪酸（FFA）、血脂的变化,同时进行高胰岛素．正葡萄糖钳夹实验观察胰岛素敏感性。两组大鼠胰腺石蜡切片,免疫荧光双标染色,标染胰岛β细胞上胰岛素受体,利用软件进行荧光强度分析。结果青年组和老年组的大鼠体重分别为（490．6±7．72）g和（728．9±7．57）g,有明显统计学意义（P〈0．01）;两组大鼠空腹血糖无明显差异,空腹胰岛素青年组为（0．59±0．14）ng／ml,老年组为（2．37±0．04）ng／ml,差异有统计学意义（P〈0．01）;空腹血清FFA水平青年组为（0．76±0．14）mmol／L,老年组为（1．51±0．04）mmol／L,有统计学差异（P〈0．01）;高胰岛素-正葡萄糖钳夹结果显示青年组大鼠葡萄糖输出速率为（26．02±2．83）mg／（kg·min）,老年组为（10．73±0．72）mg／（kg·min）,差异有统计学意义（P〈0．01）;使用稳态模型评估胰岛素分泌指数（HOMA—β）随年龄增长呈递增趋势,未达到统计学差异;而胰岛素抵抗指数（HOMA-IR）在青年组和老年组分别为3．09±0．80和13．14±1．59,差异有统计学意义（P〈0．01）：免疫荧光染色显示老年组胰岛13细胞上胰岛素受体荧光强度减弱,荧光强度分析值青年组为63．55±5．20、老年组为23．26±2．50,差异有统计学意义（P〈0．01）。结论随着年龄的增长,老年大鼠存在一定的胰岛素抵抗和代偿性胰岛素分泌增加,同时胰岛13细胞胰岛素受体减少,可能存在胰岛p细胞自身胰岛素抵抗。     

Association between birth weight and insulin sensitivity in healthy young men in Korea: role of visceral adiposity

Recent studies have demonstrated decreased insulin sensitivity in individuals with low birth weight. This study was performed to examine whether abdominal obesity is a link between insulin resistance and low birth weight. We studied the relationships between birth weight and insulin secretion, insulin sensitivity, and various anthropometric indices including visceral fat area in 22 healthy young Korean adults. Birth weight correlated significantly with diastolic blood pressure (r=-0.47, P<0.05) and insulin sensitivity index (S(I)) measured by a frequently sampled intravenous glucose tolerance test (FSIGT) (r=0.54, P<0.05), but not with insulin secretory indices such as acute insulin responses during FSIGT (r=-0.35, NS) or hyperglycemic clamp (r=0.17, NS) and submaximum insulin response during hyperglycemic clamp (r=0.10, NS). S(I) correlated significantly with abdominal obesity measurements such as waist circumference (r=-0.48, P<0.05), waist-to-hip ratio (r=-0.53, P<0.05) and visceral fat area (r=-0.58, P<0.01). However, we could not find significant correlation between birth weight and any of the abdominal obesity measurements (r=-0.35 for waist-to-hip ratio, r=-0.22 for visceral fat area, and r=-0.24 for visceral-to-subcutaneous fat ratio; NS for all). The present data confirm that low birth weight is associated with insulin resistance in adult life. However, our data suggest that the association between low birth weight and insulin resistance is not mediated by abdominal obesity.     

Effect of maternal food restriction on circulating insulin and glucagon levels and on liver insulin and glucagon binding sites of fetal and suckling rats

Food was restricted in pregnant and nursing rats in order to evaluate the effect of malnutrition on insulin and glucagon metabolism in fetal and suckling rats. Food restriction of the mothers induced a loss of body and liver weights in their offspring, which was more pronounced in suckling than in fetal rats. A significant decrease of circulating insulin and glucagon levels in fetal and suckling rats from food restricted mothers (FRM) was also observed. In liver membranes insulin binding was higher in control, fetal and suckling rats than in adult animals, but maternal food restriction decreased insulin binding to liver membranes of suckling rats, and no changes between control and fetuses from FRM were observed. By contrast, glucagon binding was higher in adult than in younger control animals; however maternal food restriction had no effect on glucagon binding to liver membranes of fetal rats, although they produced an increase in 10 day-old suckling rats. The modifications in insulin and glucagon binding reflect changes in the number of receptors, but not in the affinity constants. The time courses of insulin and glucagon association to liver membranes were unaffected by the development or by the nutritional status of the animals. Degradation of insulin and glucagon by liver membranes was significantly lower in young rats and in rats from FRM, but this does not seem to be responsible for the differences observed in binding. No significant differences in the degradation of insulin and glucagon receptors between different groups of liver membranes were found.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distinct role of adiposity and insulin resistance in glucose intolerance: studies in ventromedial hypothalamic-lesioned obese rats

It remains unclear whether adiposity plays an important role in glucose intolerance independently of insulin resistance. We investigated whether adiposity and insulin resistance had distinct roles in glucose intolerance in rats. We examined glucose tolerance and insulin resistance using ventromedial hypothalamic (VMH)-lesioned rats in the dynamic and the static phases of obesity (2 and 14 weeks after lesioning, respectively). Rats were fed either normal chow or a fructose-enriched diet (60% of total calories). The intravenous glucose tolerance test (IVGTT) was performed by bolus injection of glucose solution (1 g/kg) and blood sampling after 0, 5 10, 30, and 60 minutes. Insulin resistance was evaluated from the steady-state plasma glucose (SSPG) value during continuous infusion of glucose, insulin, and somatostatin. SSPG was not increased in VMH-lesioned rats in the dynamic phase of obesity, but increased markedly in the static phase. The area under the glucose curve (glucose AUC) during IVGTT was increased in VMH-lesioned rats in the static phase, but not in the dynamic phase, when compared with their sham-operated counterparts. A fructose-enriched diet for 2 or 14 weeks increased SSPG values to a similar extent in both sham-operated and VMH-lesioned rats without inducing excess adiposity, but glucose intolerance was only developed in the obese rats. The plasma leptin level, an excellent indicator of adiposity, was significantly related to the glucose AUC independently of the insulin level. Insulin resistance or increased adiposity alone is not sufficient to impair glucose tolerance, but increased adiposity plays an important role in the development of glucose intolerance in an insulin-resistant state.     

Effect of ageing on insulin and insulin-glucose sensitivity tests in rats

Summary Insulin tolerance tests have shown old rats to respond to injection of the hormone by a sharp and lasting drop in blood sugar. The difference between these animals and young and adult ones lies in their inability to restore a normal blood glucose level. Glucose tolerance and insulin-glucose tolerance tests show that glucose uptake under the influence of the hormone is significantly reduced with age in absolute terms. However, the difference in glucose assimilation coefficient in the absence or presence of insulin (ΔK) is comparable in all age groups; thus senile rats were found to be as sensitive even to small doses of hormone as the adult ones, if basal levels are taken into account.     

Effect of pharmacological suppression of insulin secretion on tissue sensitivity to insulin in subjects with moderate obesity

After informed consent we studied effect of pharmacological suppression of insulin secretion on tissue sensitivity to insulin in eight subjects with moderate obesity (relative body weight 133 +/- 6 per cent). Glucose tolerance (100 g oGTT) and insulin sensitivity were studied on two separate days before and after treatment with 500 mg diazoxide/d for a period of 4 d. Insulin sensitivity was determined by means of a 1-h priming dose-constant insulin infusion technique (two 30-min periods of 8 and 16 mU/kg, insulin MC-Actrapid, initiated by a start injection of 1 and 2 mU/kg, respectively). The relative decrease of plasma glucose and nonesterified fatty acid concentration at comparable steady-state insulin levels has been taken as an estimate of body sensitivity to insulin. Diazoxide treatment resulted in a significant suppression of glucose-stimulated early (insulin area 0-30 min) (P less than 0.05), late (insulin area 30-120 min) (P less than 0.01) and total insulin response (insulin area 0-120 min) (P less than 0.01) as well as a mild deterioration of glucose tolerance. Insulin sensitivity increased by about 50 per cent in comparison to the pretreatment value. Similarly, there was a marked increase of the antilipolytic effect of insulin after short-term treatment with diazoxide (P less than 0.05). The results support the concept that decreased sensitivity to insulin in obesity may be secondary due to hyperinsulinaemia.     

C-reactive protein impairs hepatic insulin sensitivity and insulin signaling in rats: role of mitogen-activated protein kinases

Plasma C-reactive protein (CRP) concentration is increased in the metabolic syndrome, which consists of a cluster of cardiovascular disease risk factors, including insulin resistance. It is not known, however, whether CRP is merely a marker of accompanying inflammation or whether it contributes causally to insulin resistance. The objective of this study is to investigate the role that CRP may play in the development of insulin resistance. We examined the effect of single-dose intravenous administration of purified human (h)CRP on insulin sensitivity in Sprague-Dawley rats using the euglycemic, hyperinsulinemic clamp technique. hCRP was associated with impaired insulin suppression of endogenous glucose production with no reduction in peripheral tissue glucose uptake, suggesting that hCRP mediated insulin resistance in the liver but not extrahepatic tissues. We further assessed components of the insulin signaling pathway and mitogen-activated protein kinases (MAPKs) in the liver. Liver tissues derived from hCRP-treated rats showed reduced insulin-stimulated insulin receptor substrate (IRS) tyrosine phosphorylation, IRS/phosphatidylinositol 3-kinase (PI3K) association, and Akt phosphorylation, consistent with hCRP-induced impairment of hepatic insulin signaling. Furthermore, hCRP enhanced phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 MAPK as well as IRS-1 Ser(612) . Finally, we observed in primary cultured rat hepatocytes that U0126 (a selective inhibitor of MAPK/ERK kinase1/2) corrected hCRP-induced impairment of insulin signaling. CONCLUSIONS: hCRP plays an active role in inducing hepatic insulin resistance in the rat, at least in part by activating ERK1/2, with downstream impairment in the insulin signaling pathway.     

Effect of moderate alcoholic beverage consumption on insulin sensitivity in insulin-resistant, nondiabetic individuals

Although moderate alcohol consumption has been associated with a decrease in plasma insulin concentrations, relatively few studies have been conducted to evaluate the effect of alcohol on insulin sensitivity, particularly in nondiabetic, insulin-resistant individuals. Because enhanced insulin sensitivity could contribute to the reported association between moderate alcohol consumption and reduced risk of heart disease and diabetes, we believed it is important to address this issue. Consequently, we evaluated the ability of moderate alcohol consumption to improve insulin sensitivity, as measured by determining the steady-state plasma glucose (SSPG) concentration during the insulin suppression test, in 20 nondiabetic, insulin-resistant individuals. Measurements were made of SSPG, glucose, insulin, and lipoprotein concentrations before and after consuming 30 g of alcohol for 8 weeks, either as vodka (n = 9) or red wine (n = 11). The SSPG concentrations (insulin resistance) decreased by approximately 8% in the total group (P = .08), and high-density lipoprotein cholesterol concentration increased by a mean of 0.09 mmol/L (P = .02). Trends were similar in individuals who consumed vodka or red wine. Men tended to have greater decline in SSPG and increase in high-density lipoprotein cholesterol compared with women. There were no other metabolic changes in fasting plasma glucose, insulin, and triglyceride concentrations. These data demonstrate that 8 weeks of moderate alcohol consumption had minimal impact on enhancing insulin sensitivity in nondiabetic, insulin-resistant individuals, raising questions as to the role, if any, of improved insulin sensitivity in the purported clinical benefits associated with moderate alcohol consumption.     

用高胰岛素-正葡萄糖钳夹实验探讨增龄对Wistar大鼠胰岛素敏感性的影响

目的探讨增龄对Wistar大鼠体重、空腹血糖、空腹胰岛素、空腹游离脂肪酸(FFA)水平及胰岛素敏感性的影响。方法将雄性Wistar大鼠45只分为4月龄组、14月龄组和24月龄组,每组15只,行高胰岛素-正葡萄糖钳夹实验,观察空腹血糖、空腹胰岛素、血清FFA和胰岛素敏感性的变化。结果 3组大鼠的体重差异有统计学意义(P<0.05,P<0.01)。与4月龄组比较,14月龄组和24月龄组大鼠空腹胰岛素、胰岛素抵抗指数明显升高(P<0.01),24月龄组大鼠血清FFA明显高于4月龄组(P<0.01);与4月龄组比较,14月龄组和24月龄组大鼠稳态葡萄糖输注速率明显降低,差异有统计学意义(P<0.01)。多元线性回归分析显示,增龄与胰岛素敏感性呈负相关。结论随着年龄的增加,大鼠空腹血糖无明显差异,空腹胰岛素和FFA均明显增加,胰岛素的敏感性降低,胰岛素抵抗加重。脂肪、肌肉和肝脏可能参与了增龄介导的胰岛素抵抗。     

Effect of dehydroepiandrosterone on insulin sensitivity in Otsuka Long-Evans Tokushima-fatty rats

In order to clarify the effect of dehydroepiandrosterone (DHEA) on improvement of insulin resistance, we examined the effects of overexpression of wild-type protein kinase C-ζ (wt-PKCζ)/3-phosphoinositide-dependent protein kinase-1 (wt-PDK1) and kinase-inactive PKCζ/PDK1 (ΔPKCζ/ΔPDK1) on DHEA-induced [³H]2-deoxyglucose (DOG) uptake using the electroporation method in rat adipocytes. Overexpression of wt-PKCζ and wt-PDK1 significantly increased in DHEA-induced [³H]2-DOG uptake. Wortmannin completely suppressed DHEA-induced [³H]2-DOG uptake in wt-PKCζ- and wt-PDK1-transfected adipocytes. Overexpression of neither ΔPKCζ nor ΔPDK1 increased DHEA-induced [³H]2-DOG uptake. Otsuka Long-Evans fatty rats (OLETF), animal models of type 2 diabetes, and Long-Evans Tokushima rats (LETO) as control, were treated with 0.4% DHEA for 2 weeks. Insulin-induced [³H]2-DOG uptakes, activations of PI 3-kinase and PKCζ of adipocytes were significantly increased in DHEA-treated OLETF rats. Moreover, plasma glucose levels in OLETF rats after treatment with DHEA for 2 weeks were significantly lower than treatment without DHEA, but not in LETO rats. These results indicate that DHEA treatment may improve glucose tolerance through a PI 3-kinase-PKCζ pathway and downregulates adiposity in OLETF rats.