Myo-inositol and sorbitol metabolism in relation to peripheral nerve function in experimental diabetes in the rat: The effect of aldose reductase inhibition

A possible relationship between increased sorbitol concentration and decreased myo-inositol concentration in peripheral nerves of diabetic rats has been examined. To this end, sorbinil, an aldose reductase inhibitor, was used either to prevent or reverse elevation of nerve sorbitol concentration in diabetic rats. Sorbinil treatment at 20 mg . kg-1 . day-1 prevented elevation of nerve sorbitol levels in early diabetes and reduced sorbitol concentration from 2.38 to 0.51 mumol/g in rats diabetic for 10 weeks. This treatment reduced the increase in nerve fructose concentration and prevented the reduced myo-inositol concentration found in diabetic rat nerve (control 3.63, diabetic 2.40, diabetic/sorbinil, 3.56 mumol/g). Sorbinil treatment did not prevent a significant slowing of motor-nerve conduction velocity at 10 weeks although treatment reduced the extent of slowing. Sorbinil treatment at 25 mg . kg-1 . day-1 reduced elevated sorbitol and fructose concentrations in diabetic in diabetic rat nerve and normalised myo-inositol concentration. Myo-Inositol treatment at 650 mg . kg-1 . day-1 did not affect the elevated concentrations of sorbitol, fructose or glucose in peripheral nerves of diabetic rats, but it did restore reduced myo-inositol concentration. Both sorbinil and myo-inositol treatment partially reversed the slowing of motor-nerve conduction velocity in diabetic rats. These results are discussed in relation to the involvement of sorbitol and myo-inositol metabolism in the aetiology of diabetic neuropathy.     

Effect of a new aldose reductase inhibitor, 8'-chloro-2',3'-dihydrospiro [pyrrolidine-3,6'(5'H)-pyrrolo[1,2,3-de] [1,4]benzoxazine]-2,5,5'- trione (ADN-138), on delayed motor nerve conduction velocity in streptozotocin-diabetic rats

The effects of a chemically new type of aldose reductase inhibitor, ADN-138, on delayed motor nerve conduction velocity (MNCV) and sciatic nerve sorbitol, fructose and myo-inositol levels were studied in streptozotocin-diabetic rats. MNCV in rats was significantly delayed after 3 weeks of diabetes and ADN-138 treatment was started at this point. Treatment of diabetics with ADN-138 at 5 and 20 but not 1 mg/kg/d for 3 weeks resulted in a significant increase in MNCV and reduced sorbitol levels to or below those of nondiabetic controls. However, fructose, though decreased in a dose-dependent manner, was not normalized. The reference drug, Sorbinil, showed similar effects on them. After the 3 weeks of ADN-138(20 mg/kg/d) treatment, diabetics were left on ADN-138 or continued further to be treated with it for 3 weeks. The withdrawal of ADN-138 prevented a further increase in MNCV and restored sorbitol and fructose to nontreated diabetic levels, and myo-inositol levels declined. In contrast, the ADN-138-continued group kept improving its MNCV and normalized sorbitol and myo-inositol. These results suggest that polyol accumulation is responsible for delayed MNCV and that the action of ADN-138 on MNCV reflected reversibility of metabolic function in diabetics.     

Increase in cardiac muscle fructose content in streptozotocin-induced diabetic rats.

To evaluate the activation of the sorbitol pathway in cardiac muscle in diabetic rats, we measured sorbitol, fructose, and myo-inositol content in cardiac tissue obtained from control and streptozotocin-diabetic rats, with or without an 8-week insulin treatment, using gas chromatography-mass spectrometry (GC-MS). Cardiac fructose and sorbitol content in 10-week diabetic rats increased by 60-fold and 3.9-fold of those of control rats, respectively (P less than .001). In contrast, cardiac myo-inositol content in 10-week diabetic rats decreased to 56% (P less than .025) of the control value. The abnormalities in cardiac fructose, sorbitol, and myo-inositol content were completely normalized by the 8-week insulin treatment, which was initiated 2 weeks after the induction of diabetes. There was no difference in cardiac aldose reductase activity between control and diabetic rats. However, cardiac sorbitol dehydrogenase activity in diabetic rats was 151% (P less than .005) higher than that of control rats, although hepatic sorbitol dehydrogenase activity was not different between the two groups. These results indicate that the sorbitol pathway is significantly activated in cardiac tissue obtained from streptozotocin-induced diabetic rats, which results in the marked cardiac accumulation of fructose.     

Statil-sensitive polyol formation in nerve of galactose-fed mice

The sciatic nerve of diabetic C57BL/Ks mice did not accumulate either sorbitol or fructose despite elevated nerve glucose levels, nor did they show a depletion of free myo-inositol. Galactose feeding of both nondiabetic and diabetic mice for five days resulted in marked accumulations of dulcitol in nerve indicating polyol forming activity. Levels of myo-inositol showed small elevations in nerves of galactose-fed mice which reached significance when compared to diabetic mice fed the standard diet. Dulcitol accumulation was prevented by concurrent administration of the aldose reductase inhibitor Statil, but this did not prevent the increased levels of myo-inositol.     

Altered bone metabolism in db/db mice]

Bone and calcium metabolism was investigated in genetically obese, diabetic db/db mice and compared with that in a new hypoglycemic agent (AS-6) treated db/db mice and in their lean litter mates as controls. The 5-week-old db/db mice (serum Ca 9.88 +/- 0.22 mg/dl, glucose 258.6 +/- 13.3 mg/dl) were randomly divided into two groups. One group, together with their lean litter mates, was fed a commercial diet (CE-2). The other db/db group was fed CE-2 diet containing 0.1% of AS-6. Both groups were fed for 20 weeks. The serum glucose and calcium levels in db/db control groups (serum Ca 12.3 +/- 0.1 mg/dl, glucose 650.2 +/- 23.9 mg/dl) were higher than those in lean control groups (Ca 9.8 +/- 0.2 mg/dl, glucose 180.7 +/- 10.1 mg/dl). The wet, dry and ashed weights of the femur in db/db control were significantly lower and the length of femur in db/db control was significantly shorter than those of lean controls. These data suggest that retarded bone growth in db/db mice is related to progression of diabetes. Although, there was no change in Ca/P, Ca/ash and total perimeter in femurs, the cortical area in the femurs of db/db control mice (0.65 +/- 0.02 mm2) was significantly smaller than that of the femurs of lean control mice (0.74 +/- 0.02 mm2). The cortical bone thinning observed in the db/db control could have been caused by increased bone resorption. Treatment with AS-6 for 20 weeks resulted in a 48.6% decrease of serum glucose and 5.2% decrease of calcium as compared with db/db controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Combined therapy of rhein and benazepril on the treatment of diabetic nephropathy in db/db mice.

OBJECTIVE: Rhein and angiotensin-converting enzyme inhibitor (ACEI) have been reported to prevent the progression of diabetic nephropathy (DN). We further explore the unknown ability to induce renal-protection of rhein and ACEI combined therapy in DN compared with the therapeutic effects of single treatment of them by using db/db mouse of type 2 diabetes model. METHODS: db/db and db/m mice, 8 weeks of age, were divided into five groups according to the following treatments: (A) db/m, given saline treatment; (B) db/db, given saline treatment; (C) db/db, given rhein treatment (150 mg/kg/day); (D) db/db, given benazepril treatment (10 mg/kg/day); (E) db/db, given rhein (150 mg/kg/day) with benazepril (10 mg/kg/day). Body weight, plasma glucose, plasma lipid and 24 h urinary albumin excretion levels were measured every 4 weeks. Morphometry of renal tissue and immunohistology of transforming growth factor-beta1 (TGF-beta) and fibronectin were determined for all groups at the end of the treatment. RESULTS: It was found that after treatment urinary albumin excretion was reduced after 4 weeks treatment in group E and after 8 weeks treatment in groups C and D, when compared to group B (p<0.05). Plasma creatinine levels dropped significantly for group E, compared with the diabetic control group by the end of the treatment period. Furthermore, after the treatment body weight, plasma glucose, cholesterol, triglyceride and low density lipoprotein all decreased in groups C and E compared to group B (p<0.05). Histological morphometric analysis revealed that the whole glomerular area and extracellular matrix area was significantly reduced in groups C, D and E compared to group B, at 20 weeks of age, an effect most pronounced in group E. Using immunohistochemistry, the expression of fibronectin and TGF-beta1 in groups C, D and E was found to have decreased compared to group B, after 12 weeks treatment, again the effect being more pronounced in group E. CONCLUSIONS: There appeared to be a similar renal protective effect of rhein compared with benazepril in diabetic nephropathy. A combined therapy may offer a more beneficial complementary effect on kidney injury in db/db mice, as reflected by urinary albumin excretion, renal function and histological changes. Our findings suggest that a therapeutic approach that combines rhein with ACEI provides a more effective therapy for DN than does either agent alone.     

Essential fatty acid treatment — effects on nerve conduction,polyol pathway and axonal transport in streptozotocin diabetic rats

Summary This study was designed to examine the effect of dietary supplementation with essential fatty acids (evening primrose oil — 5% weight:weight added to the diet) on acute neurophysiological and neurochemical defects in streptozotocin-diabetic rats. Diabetic rats, which were not given evening primrose oil, showed highly significant elevations of nerve sorbitol and fructose combined with a depletion of nerve myo-inositol. In those animals there was also a 40% reduction (p<0.02) in the accumulation of axonally transported substance P-like immunoreactivity proximal to a 12 h sciatic nerve ligature together with reduced motor nerve conduction velocity (13% [p<0.001] and 20% [p<0.001] in two separate experiments). Treatment of other diabetic rats with evening primrose oil prevented completely the development of the motor nerve conduction velocity deficit without affecting sorbitol, fructose or myo-inositol levels or the deficit in axonal transport of substance P. In a second experiment, treatment of diabetic rats with evening primrose oil was associated with significant attenuation of the conduction velocity deficit, but not complete prevention.     

雷公藤甲素治疗db／db糖尿病小鼠的疗效观察

目的:利用db/db小鼠验证雷公藤甲素对糖尿病肾脏损伤的治疗作用,探讨雷公藤甲素防治糖尿病肾病的机制. 方法:9周龄的db/db和db/m小鼠分为五组:(1)db/m正常对照组;(2)dh/dh糖尿病对照组;(3)缬沙坦治疗纽;(4)雷公藤甲素低剂最治疗组;(5)雷公藤甲素高剂繁治疗组.于4周、8周及12周测定各组24h尿白蛋白、血生化和体重.光镜观察肾小球病变,电镜观察足突改变,并作定量分析.免疫病理观察足细胞裂孔膜蛋白nephrin,足细胞损伤标志物desmin,炎症反应标志物单核细胞趋化蛋白1(MCP-1),氧化应激标志物4羟壬烯醛(4-HNE)的表达. 结果:db/db小鼠经雷公藤甲素治疗后蛋白尿下降,肾小球肥大和足细胞损伤减轻,肾组织炎症和氧化应激状态改善,同时高血脂和肥胖减轻.该作用随治疗时间延长,效果更加明显,且高剂量疗效优于低剂量.雷公藤甲素降低蛋白尿、改善肾小球肥大的作用与缬沙坦相似,但降低肾组织炎症和氧化应激的作用雷公藤甲素比缬沙坦更强. 结论:雷公藤甲索能明显降低dh/db小鼠尿蛋白的排泄,减轻肾组织炎症反应,改善肾脏组织病变,对糖尿病肾脏损伤具有显著且更全面的治疗作用.     

2型糖尿病模型db/db小鼠海马超微结构观察

目的：观察2型糖尿病动物模型－C57BL／KsJ(db/db)小鼠海马超微结构变化,方法：糖尿病组：6周龄C57BL／KsJ(db/db)小鼠5只,尾静脉空腹血糖高于11．1mmol/L且肥胖,对照组;非糖尿病小鼠C57BL／KsJ5只,尾静脉空腹血糖低于6．0mmol/L,体重正常,于30周龄（成模第6个月要）时,灌注固定取脑,透射电镜下观察海马CAI区,结果：糖尿病小鼠海马超微结构发生显著改变包括锥体细胞退变,髓鞘崩解,突触变性等。结论：糖尿病所致海马超微结构改变可能与糖尿病学习记忆功能减退有关。     

Clinical usefulness of measuring urinary polyol excretion by gas-chromatography/mass-spectrometry in type 2 diabetes to assess polyol pathway activity

INTRODUCTION: Decreased myo-inositol levels and increased activity of the polyol pathway have been proposed to play a role in causing diabetic microvascular complications. There are few clinical methods for examining the activity of the polyol pathway in diabetic patients. We assessed the effect of changes in glycemic control on polyol pathway activity by measuring urinary polyol excretion. MATERIALS AND METHODS: Gas-chromatography/mass-spectrometry (GC/MS) was used to assess the urinary excretion of glucose and polyols (myo-inositol, sorbitol, and fructose) in 50 patients who had type 2 diabetes without nephropathy and 20 healthy subjects. RESULTS: In the diabetic patients with poor glycemic control, urinary sorbitol levels were significantly increased and urinary myo-inositol excretion was approximately 6.5-fold higher than in healthy controls (33.0+/-6.5 vs 221.7+/-45.9 mg/day, mean+/-SE, P<0.01). During strict glycemic control, some patients (Group A) showed simultaneous disappearance of glucosuria and normalization of the urinary excretion of myo-inositol (<50 mg/day) and, while others (Group B) showed delayed normalization of urinary myo-inositol excretion. Group B showed significantly higher urinary myo-inositol, sorbitol, and fructose excretion than Group A at the time of disappearance of glucosuria. These findings suggest that patients in Group B may have increased polyol pathway activity. CONCLUSION: Even though short-term strict glycemic regulations were established in long-standing hyperglycemic diabetic patients, to normalize the once-exaggerated polyol pathway activities, it was essential to maintain glucosuria-free conditions for some period. Quantitation of urinary polyols using GC/MS appears to be a clinically useful method for assessing polyol pathway activity.     

Effects of a new aldose reductase inhibitor, (2S, 4S)-6-fluoro-2',5'-dioxospiro[chroman-4,4'-imidazolidine]-2-ca rboxamid e (SNK-860), on the slowing of motor nerve conduction velocity and metabolic abnormalities in the peripheral nerve in acute streptozotocin-induced diabetic rats.

The effects of a new aldose reductase inhibitor (ARI), (2S,4S)-6-fluoro-2',5'-dioxospiro[chroman-4,4'-imidazolidine]-2-ca rboxamide (SNK-860), on the slowing of motor nerve conduction velocity (MNCV) and metabolic abnormalities in sciatic nerve were investigated in acute streptozotocin (STZ)-induced diabetic rats. MNCV in the diabetic rats was significantly slower 2 weeks after STZ injection. In the following 2 weeks, treatment with SNK-860 improved MNCV in a dose-dependent manner. The efficacy of 1 mg/kg SNK-860 was equipotent to that of 20 mg/kg sorbinil. Four weeks after STZ injection, increases in sorbitol levels, decreases in myo-inositol levels, and reductions in Na+, K(+)-adenosine triphosphatase (ATPase) activity were observed in sciatic nerves of diabetic rats. Administration of SNK-860 for 14 days beginning 2 weeks after the induction of diabetes inhibited these metabolic abnormalities in a dose-dependent manner. SNK-860 restored all of these parameters to normal levels at a dose of 2 mg/kg. In addition, close correlations were observed between MNCV and sorbitol levels (r = -.95) and between MNCV and myo-inositol levels (r = .93) in the sciatic nerve; a close correlation was also observed between sorbitol and myo-inositol levels in the sciatic nerve (r = -.86). Therefore, it is suggested that the effect of SNK-860 on the slowing of MNCV results from normalizing the above-mentioned metabolic abnormalities in the sciatic nerve of diabetics. Thus, SNK-860 may be useful in the treatment of diabetic neuropathy.     

Characterization of a novel aldose reductase inhibitor, FR74366, and its effects on diabetic cataract and neuropathy in the rat

FR74366 (FK366) ([3-(4-bromo-2-fluorobenzyl)-7-chloro-2,4-dioxo-1,2,3,4- tetrahydroquinazolin-1-yl] acetic acid) is a chemically novel aldose reductase (AR) inhibitor. It exhibited a highly potent, reversible, and mixed type inhibition of partially purified AR from the rat sciatic nerve (IC50 = 3.6 nmol/L) and rat lens (IC50 = 4.4 nmol/L). FR74366 inhibited sorbitol accumulation in the isolated human erythrocyte (IC50 = 1.6 mumol/L), rat lens (IC50 = 39 mumol/L), and rat sciatic nerve (IC50 = 17 mumol/L) incubated with high glucose concentrations. The oral administration of FR74366 to streptozotocin (STZ)-induced diabetic rats for 2 weeks decreased sorbitol levels (ED50 = 3.7 mg/kg for sciatic nerve, 23 mg/kg for lens, 52 mg/kg for retina, and 62 mg/kg for renal cortex). Administration of FR74366 to diabetic rats for 17 weeks delayed cataract formation and admixture of 0.028% FR74366 in the diet completely inhibited the cataract formation. Moreover, the recovery of reduced motor nerve conduction velocity by FR74366 in diabetic rats was demonstrated in prevention and reversal experiments. This recovery effect correlated well with reduction of accumulated sorbitol and fructose levels and normalization of decreased myoinositol levels. The duration and tissue specificity of inhibitory effects of FR74366 on sorbitol accumulation also correlated well with the levels of FR74366 in various tissues of diabetic rats. These data indicate that both decreases in tissue sorbitol levels and improvement of functional defects reflect FR74366 levels in tissue rather than plasma in diabetic rats. These results, taken together, suggest that FR74366, which is currently undergoing clinical trials in Japan and the United States, will be a useful therapeutic agent for diabetic complications.     

Enteroinsular axis of db/db mice and efficacy of dipeptidyl peptidase IV inhibition

In type 2 diabetic patients, the administration of glucagon-like peptide-1 (GLP-1), known as an incretin, exerts antidiabetic effects. However, GLP-1 is rapidly degraded by dipeptidyl peptidase IV (DPPIV) after its release. DPPIV inhibition is thought to be a rational strategy to treat type 2 diabetes. In this study, using C57BLKS/J-db/db (db/db) mice as a model of type 2 diabetes, we examined the effect of acute DPPIV inhibition on glucose tolerance at the early and later stages of diabetes, determining plasma active GLP-1 and insulin levels. In addition, we investigated changes of plasma DPPIV activity. Compared with normal C57BL6/J (B6) and db/+ mice, significantly increased plasma DPPIV activities were observed in db/db mice. Expression of the proglucagon gene encoding GLP-1 was significantly upregulated in the colon of db/db mice. The administration of valine-pyrrolidide, a DPPIV inhibitor, resulted in potentiated insulin secretion mediated by increased endogenous GLP-1 action, leading to improved glucose tolerance in db/db mice at 6 weeks of age. However, although acute DPPIV inhibition with valine-pyrrolidide resulted in higher plasma active GLP-1 and insulin levels in db/db mice at 23 weeks of age, it did not improve glucose tolerance. The function of the enteroinsular axis is preserved in both stage of diabetes and the DPPIV inhibitor potentiated it, but the progression of insulin resistance appeared to block the improvement of glucose tolerance through DPPIV inhibition. Our results suggest that DPPIV inhibition is a suitable approach for treatment of impaired glucose tolerance (IGT), and type 2 diabetes in the early stage.     

Effects of 15-month aldose reductase inhibition with fidarestat on the experimental diabetic neuropathy in rats

We examined the effects of long-term treatment with an aldose reductase inhibitor (ARI) fidarestat on functional, morphological and metabolic changes in the peripheral nerve of 15-month diabetic rats induced by streptozotocin (STZ). Slowed F-wave, motor nerve and sensory nerve conduction velocities were corrected dose-dependently in fidarestat-treated diabetic rats. Morphometric analysis of myelinated fibers demonstrated that frequencies of abnormal fibers such as paranodal demyelination and axonal degeneration were reduced to the extent of normal levels by fidarestat-treatment. Axonal atrophy, distorted axon circularity and reduction of myelin sheath thickness were also inhibited. These effects were associated with normalization of increased levels of sorbitol and fructose and decreased level of myo-inositol in the peripheral nerve by fidarestat. Thus, the results demonstrated that long-term treatment with fidarestat substantially inhibited the functional and structural progression of diabetic neuropathy with inhibition of increased polyol pathway flux in diabetic rats.     

Relation of Na+, K(+)-ATPase to delayed motor nerve conduction velocity: effect of aldose reductase inhibitor, ADN-138, on Na+, K(+)-ATPase activity

The role of sorbitol, myo-inositol, and Na+, K(+)-adenosine triphosphatase (ATPase) activity on motor nerve conduction velocity (MNCV) in streptozotocin (STZ)-diabetic rats was studied. Reduction of MNCV and Na+, K(+)-ATPase in caudal nerves appeared after 3 weeks of diabetes, and at this time treatment with aldose reductase inhibitor (ARI), ADN-138 and 1% myo-inositol supplement was begun. One percent myo-inositol supplement for 3 weeks resulted in a significant increase in myo-inositol levels in diabetic nerves, but left MNCV and sorbitol levels unchanged. In contrast, treatment with ADN-138 for 3 weeks reduced sorbitol levels in diabetic nerves and resulted in significant increases in MNCV and Na+, K(+)-ATPase in the nerves. Since ADN-138 did not restore myo-inositol levels, the increase in Na+, K(+)-ATPase levels by ADN-138 treatment was independent of myo-inositol levels. Also, nerve Na+ levels in ADN-138-treated rats were reduced and the ratio of K+ to Na+ was raised, while 1% myo-inositol supplement did not affect them. These results suggest that treatment with ADN-138 elevates MNCV through a series of processes: ARI----reduction of sorbitol level----increase in Na+, K(+)-ATPase activity----correction of K+, Na+ imbalance----increase in MNCV.     

Osmotically-induced nerve taurine depletion and the compatible osmolyte hypothesis in experimental diabetic neuropathy in the rat

Summary Diabetic neuropathy results from progressive nerve fibre damage with blunted nerve regeneration and repair and may be complicated by nerve hyperexcitability resulting in pain. The naturally occurring amino acid taurine functions as an osmolyte, inhibitory neurotransmitter, and modulator of pain perception. It is also known to have neurotrophic actions. The compatible osmolyte hypothesis proposes that levels of intracellular organic osmolytes including taurine and myo-inositol, respond co-ordinately in response to changes in intracellular sorbitol or external osmolality to maintain the intracellular milieu. We hypothesize that glucose-induced sorbitol accumulation in diabetes mellitus will result in taurine depletion in peripheral nerve which may potentially impair nerve regeneration and precipitate neuronal hyperexcitability and pain. This study explored the relationships of taurine, myo-inositol and sorbitol in the rat nerve and their effects on nerve conduction velocity. Osmolyte levels and nerve conduction velocity were determined in sciatic nerve from non-diabetic and streptozotocin-induced diabetic rats, with or without dietary taurine or myo-inositol supplementation. Taurine levels decreased by 31% (p< 0.01) and myo-inositol decreased by 37% (p<0.05) in diabetic nerve as sorbitol accumulated. Taurine supplementation of diabetic animals did not affect nerve conduction velocity but further reduced nerve myo-inositol levels. Prevention of sorbitol accumulation with the aldose reductase inhibitor sorbinil increased nerve taurine levels by 22% (p<0.05) when compared with untreated diabetic animals. Thus, we have demonstrated an interdependence of organic osmolytes within the nerve. Abnormal accumulation of one osmolyte results in reciprocal depletion of others. Diabetic neuropathy may be an example of maladaptive osmoregulation, nerve damage and instability being aggravated by taurine depletion.     

Effects of antidiabetic treatment with metformin and insulin on serum and adipose tissue adiponectin levels in db/db mice

Decreased circulating levels of adiponectin, a novel adipose-derived adipocytokine, in obesity possibly contribute to the development of insulin resistance which is a major factor in the pathogenesis of type 2 diabetes. The present study was conducted to examine whether circulating and adipose tissue adiponectin levels are modulated by chronic treatment with metformin and intensive treatment with insulin in murine models of obesity and type 2 diabetes, db/db mice with a C57BL/KsJ genetic background. Nine-week-old male db/db mice were treated with metformin, insulin, and vehicle for 4 weeks. Expectedly, metformin treatment led to inhibition of weight gain and improvement of hyperinsulinemia. Insulin treatment lowered fasting blood glucose levels to normal values, although it sustained hyperinsulinemic state. However, after 4 weeks of treatment, serum adiponectin levels were not significantly elevated in either metformin-treated or insulin-treated db/db mouse group (14.2 +/- 0.7 and 16.7 +/- 1.0 microg/ml, respectively) compared to vehicle-treated group (14.9 +/- 0.6 microg/ml). Similarly, adipose tissue adiponectin levels determined by Western blot analysis were not increased in either metformin-treated or insulin-treated group relative to vehicle-treated group. Recent studies have shown that adiponectin possibly has the same physiological effects on lipid and glucose metabolism that metformin has. Therefore, an elevation in blood concentration of metformin following the treatment might lead to suppression in adiponectin synthesis in adipose tissue, independent of inhibition in weight gain and improvement in hyperinsulinemia by metformin treatment. The present results indicate that adiponectin is not involved in the mechanism by which metformin treatment enhances insulin sensitivity. Moreover, our results suggest that adiponectin synthesis in adipose tissue may be suppressed under hyperinsulinemic state sustained by insulin treatment, even though hyperglycemia is markedly reduced. We conclude that antidiabetic treatment with metformin and insulin does not affect circulating and adipose tissue adiponectin levels.     

Sorbitol accumulation is altered in Type 1 (insulin-dependent) diabetes mellitus

Summary Intracellular sorbitol accumulation has been implicated as an aetiological factor for many of the complications of diabetes mellitus. Erythrocyte sorbitol is found in higher concentration in Type 1 (insulin-dependent) diabetic patients than in normal subjects. When sorbitol accumulation is corrected for its immediate prescursor glucose (sorbitol/glucose ratio), the polyol accumulation remains significantly greater in erythrocytes from the Type 1 diabetic. Erythrocytes from Type 1 diabetic patients exposed to normal extracellular glucose concentrations for 3 h in vitro, accumulate more sorbitol and fructose than normal cells in the same incubation system. Near-normalization of plasma glucose in Type 1 diabetic patients for 12 h did not result in normal erythrocyte sorbitol levels. The increased sorbitol accumulation in erythrocytes from Type 1 diabetic subjects may reflect similar activity in the lens and nerve in long-standing diabetes. This increased sorbitol production was found in most, but not all, individuals with diabetes and appears to be an acquired characteristic. Those factors influencing enhanced tissue sorbitol accumulation may be important in the aetiology of diabetes-associated complications.     

The development of obesity in genetically diabetic-obese (db/db) mice pair-fed with lean siblings

Summary The importance of reduced thermoregulatory thermogenesis as a mechanism for the high metabolic efficiency of the diabetic-obese (db/db) mouse has been investigated. Young db/db mutants were pair-fed to the ad libitum food intake of lean siblings for two weeks at two different environmental temperatures, 23 and 33 °C. At 23 °C, a temperature at which there is a substantial demand for thermoregulatory thermogenesis, the diabetic-obese animals deposited 51% more total energy and 75% more fat than the lean mice. At 33 °C (thermoneutrality) where there is no requirement for thermoregulatory heat, the mutants deposited 25% more fat than lean animals, but there was no significant difference in the total energy gain of the two groups. Pair-feeding resulted in a reduced protein deposition at both temperatures in the diabetic-obese animals compared to the lean. It is concluded that the high metabolic efficiency of the diabetic-obese mutant, like that of the obese (ob/ob) mouse, is caused by a low energy expenditure on thermoregulatory thermogenesis.     

Metabolic abnormalities of the hyperglycemic obese Zucker rat.

In a cross-sectional study, we evaluated the metabolic profiles of lean (Fa/?) and obese (fa/fa) Zucker male rats at 4 to 8 months of age. Although all of the obese rats (N = 108) demonstrated glucose intolerance, most of the obese rats exhibited only mild elevations of fasted and fed plasma glucose. Only 14 of the obese rats were severely hyperglycemic, which resulted in substantial elevations of glycohemoglobin (GHb) levels. The nerve and lens levels of glucose, sorbitol, and fructose were elevated, and the myo-inositol was depleted in all hyperglycemic obese rats, but not in the euglycemic obese rats. With increasing duration of hyperglycemia, the neural myo-inositol level approached normal, while the lenses became cataractous. All obese rats had increased urinary albumin excretion (UAE), which was dependent on age (r = .45, P less than .02) and independent of hyperglycemia, glucosuria, and polyuria. In conclusion, although the euglycemic obese rats exhibited some diabetic abnormalities, the hyperglycemic obese Zucker rat more closely resembled the altered metabolic profile associated with type II diabetes mellitus.