bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduced Urinary Insulin Clearance in Patient With Abnormal Insulinemia
Authors: Yamamoto Ritsuko , Iwamoto Yasuhiko , Sakura Hiroshi , Yoshioka Narihito , Hsieh Shiun-Dong , Matsuda Ayako , Kuzuya Takeshi
Published: September 2013

We recently reported a new case of abnormal insulinemia with LeuA3 insulin. Herein, we measured urinary insulin clearance during oral glucose tolerance tests in a proband with abnormal insulinemia (44-yr-old female), three affected family members, two unaffected family members, two other hyperinsulinemic patients with obesity, five non-insulin-dependent diabetic patients, and five normal control subjects. Urinary insulin-to-creatinine clearance ratio in the proband and her affected family members was 0.22 × 10−3 ± 0.07 (mean ± SD, n = 4) and was markedly reduced compared with those of other groups: 1.73 × 10−3 in two unaffected family members, 2.77 × 10−3 in two other hyperinsulinemic patients with obesity, 2.99 × 10−3 ± 1.48 in five non-insulin-dependent diabetic patients, and 2.54 × 10−3 ± 0.67 in five normal control subjects. In contrast, urinary C-peptide clearance in these groups was not significantly different from controls. Binding of immunopurified insulins extracted from urine of the patients with abnormal insulinemia to guinea pig kidney membrane was slightly decreased (71% of standard insulin), in contrast with the observation that serum insulin of the proband had much less receptor-binding activity. Reverse-phase HPLC analysis of the immunopurified insulin of the proband revealed that the ratios of normal insulin to abnormal insulin were 8:3 in urine and 1:7 in serum, respectively. These results suggest that excretion of abnormal insulin in urine is much less than that of normal insulin.
Abnormalities in Glucose-Stimulated Insulin Release, 45Ca Uptake, and 86Rb Efflux in Diabetic Chinese Hamster Islets
Authors: Frankel Barbara J , Sehlin Janove
Published: September 2013

We loaded islets from normal and diabetic Chinese hamsters with 86Rb (an analogue for K+) and measured 86Rb efflux during stimulation with 20 mM D-glucose. Genetically diabetic Chinese hamsters were selected from a subline (L) known for subnormal pancreatic insulin release and excessive pancreatic glucagon release in vitro. 86Rb accumulation in 1 mM glucose was normal in the diabetic islets. Similar to the pattern of 86Rb efflux previously seen from normal rat and mouse islets, 20 mM glucose suppressed 86Rb efflux within 1-2 min, and efflux remained suppressed until return to 1 mM glucose in both normal and diabetic hamster islets. After the first 2 min of 20 mM glucose, suppression of 86Rb efflux was somewhat greater in the diabetic hamster islets than in the normals. In addition, glucose-stimulated insulin release and 45Ca uptake were significantly reduced in the diabetic islets. Therefore, in the diabetic hamster islets, there is at least no impairment in the initial suppression of 86Rb efflux by glucose. This suggests that the diabetic β-cells recognize glucose and carry out the initial steps in the stimulus-secretion coupling sequence normally. The later, excessive suppression of 86Rb efflux may be due to impaired Ca2+-induced changes in 86Rb efflux, suggesting that defective regulation of intracellular Ca2+ activity, rather than defective regulation of K+ permeability, may lead to the impaired insulin secretion.
Somatostatin Impairs Clearance of Exogenous Insulin in Humans
Authors: Ipp Eli , Sinai Yosef , Bar-Oz Benjamin , Nesher Rafael , Cerasi Erol
Published: September 2013

Somatostatin has been widely used to suppress endogenous pancreatic hormone secretion in research studies. Many of these studies required the simultaneous infusion of a hormone together with somatostatin. A critical assumption for its use in metabolic investigation is that somatostatin has no effect on the action or clearance of a concomitantly infused hormone. To test whether clearance of an exogenously infused hormone is affected, we infused insulin with or without somatostatin in two sets of studies. Insulin (40 mU · kg−1 · h−1) was infused for 100 min (n = 6). Plasma glucose levels fell to 55 ± 4.1 mg/dl with insulin alone and significantly lower, to 44 ± 1.9 mg/dl, when somatostatin (250 μg/h) was also infused (P < .01). Plasma immunoreactive insulin (IRI) rose to 57 ± 12.5 μU/ml with insulin alone, which was significantly different from 88 ± 15 μU/ml when insulin was infused together with somatostatin (P < .01). When a smaller dose of insulin (30 mU kg−1 h−1) was infused for 100 min (n = 4), similar results were observed. When somatostatin was infused together with insulin, plasma glucose fell to lower levels (41 ± 4.2 vs. 62 ± 9.5 mg/dl; P < .01) and plasma IRI rose higher (39 ± 8.5 vs. 27 ± 5.9 μU/ml; P < .01) than when insulin was infused alone. C-peptide was equally suppressed by hypoglycemia regardless of whether somatostatin was administered, indicating suppression of endogenous insulin during these studies. We conclude that somatostatin infusion impairs the clearance of exogenous insulin. The resulting higher plasma IRI levels may contribute to the exaggerated hypoglycemia observed when somatostatin is infused with insulin. Impairment of clearance must be considered in the interpretation of metabolic studies where insulin and perhaps other peptide hormones are infused together with somatostatin.
Immunological and Metabolic Concomitants of Cyclosporin Prevention of Diabetes in BB Rats
Authors: Yale J-F , Grose M , Seemayer T A , Marliss E B
Published: September 2013

The metabolic and immunological effects of cyclosporin given to prevent diabetes in BB rats were examined. Diabetes-prone (BBdp) and normal (BBn) BB rats received either oral cyclosporin (10 mg · kg−1 · day−1 or its vehicle from age 30-150 days. Six of 21 (29%) vehicle-treated rats became glycosuric, with hyperglycemia, weight loss, and unremitting insulin requirements, and showed destruction of islet β-cells. Five of 24 (21%) cyclosporin-treated rats became glycosuric, but none demonstrated weight loss, all required insulin only intermittently after onset, and all showed persistence of islet β-cells. Cyclosporin induced hypoinsulinemic glucose intolerance in BBn rats.

Cyclosporin inhibited the normal rise with age of peripheral blood lymphocyte cell numbers, identified with monoclonal antibodies. OX19+ (pan-T) and W3/25+ helper T-lymphocytes were affected, and there was an increase in the large W3/13+ OX19− population characteristic of BBdp rats; in addition, this subset appeared in BBn rats. Cyclosporin also caused the appearance and/or increase in both BBdp and BBn rats of W3/25+OX19− and OX8+ OX19− subsets. Suppressor/cytotoxic (OX8+) T-lymphocytes and la+ cells were less affected.

The incidence of hyperglycemia and glycosuria was therefore unaltered by cyclosporin, although the diabetic syndrome was milder. BBn rats receiving cyclosporin showed glucose intolerance, suggesting that in BBdp rats, the net effects of immunosuppression on β-cell destruction may have been counterbalanced by the direct effect on the same cells. The attenuation of diabetes in BBdp rats occurred through further immunosuppression rather than by correction of its preexisting immunodeficiency.
Galactose Neuropathy: Structural Changes Evaluated by Nuclear Magnetic Resonance Spectroscopy
Authors: Griffey Richard H , Eaton R Philip , Gasparovic Charles , Sibbitt Wilmer
Published: September 2013

We examined the hypothesis that the polyol accumulation resulting from chronic galactose supplementation in the diet produces endoneurial edema that can be prevented by inhibition of aldose reductase. We explored the potential of nuclear magnetic resonance (NMR) spectroscopy to quantitate and characterize the water accumulation in the sciatic nerve in this “galactose neuropathy.” The data demonstrate a 16% increase in gravimetrically determined total water content of nerve in the galactose-fed rat after 8 mo of this diet and a 50% increase in the T1 relaxation time for nerve water as determined by NMR spectroscopy. Prolongation of the T1 relaxation time reflects increased rotation of water in a magnetic field, consistent with an extracellular site of the additional water. Simultaneous feeding of sorbinil to inhibit aldose reductase resulted in normalization of both total nerve water and of the prolongation of T1 relaxation time. These data define the NMR-spectroscopic state of endoneurial edema in the galactose-fed rat and suggest specific application to the investigation of the role of aldose reductase in human diabetic neuropathy.
Role of the Oropharynx in Regulation of Glycemia
Authors: Proietto Joe , Rohner-Jeanrenaud Françoise , Ionescu Elisabeth , Jeanrenaud Bernard
Published: September 2013

Previous studies have demonstrated that reflexes originating from the oral cavity at the start of food intake are necessary to ensure a normal glucose tolerance. In our experiment, the underlying mechanisms of these reflexes were studied in conscious, freely moving rats bearing chronic catheters. A double-isotope technique was used to measure, under non-steady-state conditions, rates of total glucose appearance (total Ra), total glucose disappearance (Rd), gut glucose absorption (gut Ra), hepatic glucose production (HGP), and the metabolic clearance rate of glucose (MCRg). In random order, 1 wk apart, rats either spontaneously drank 1 ml of a 60% glucose solution or were given the same dose into the stomach via a chronic gastric catheter. Glycemia and insulinemia were lower when glucose was taken orally than when the same amount of the substrate was administered intragastrically. Total Ra after glucose administration was the same in both groups throughout the experiment. Despite lower insulin and glucose values, the increase in Rd was initially higher in the oral group than in the intragastric group. This was accompanied by initial higher MCRg values in the oral group than in animals that received the glucose load directly into their stomachs. We conclude that a series of reflexes elicited by oral glucose ingestion improve glucose tolerance by increasing the efficiency of glucose disposal in the early stages after a glucose load, with a smaller amount of insulin released.
Basal and Meal-Induced Somatostatln-Like Immunoreactivity in Healthy Subjects and in IDDM and Totally Pancreatectomized Patients: Effects of Acute Blood Glucose Normalization
Authors: Gutniak Mark , Grill Valdemar , Wiechel Karl-Ludwig , Efendić Suad
Published: September 2013

We investigated the impact of blood glucose normalization on plasma levels of somatostatin-like immunoreactivity (SLI) in subjects with C-peptidenegative insulin-dependent diabetes mellitus (IDDM) and in totally pancreatectomized patients. Patients were studied during hyperglycemia and during normoglycemia, which was attained by Biostatordirected feedback insulin infusion. The experiments were performed in the fasted state and after a standardized breakfast. In IDDM (n = 6), basal levels of SLI were significantly higher than in nondiabetic subjects (n = 18). In IDDM, normalization of hyperglycemia was followed by a 40% decline in basal SLI (P < .05). After the meal, SLI increased to the same absolute levels with or without feedback insulin treatment; however, the incremental response was 60% higher during feedback insulin treatment (P < .05). Treatment also suppressed fasting and postprandial levels of glucagon, whereas gastric inhibitory polypeptide (GIP) levels were unaltered. In four pancreatectomized patients, normoglycemia tended to lower plasma levels of SLI by 50% (P < .1). After breakfast, an SLI response was noted during normoglycemia, whereas no significant effect of the meal was seen during hyperglycemia. We conclude that in IDDM and in totally pancreatectomized patients, administration of insulin with subsequent normalization of blood glucose is accompanied by a decline in plasma levels of SLI in the fasted state, whereas the apparent response to a meal is enhanced. These effects on plasma levels of SLI probably reflect to a major extent release of somatostatin from the gastrointestinal tract.
Genetic, Immunologic, and Environmental Heterogeneity of IDDM: Incidence and 12-Mo Follow-Up of an Italian Population
Authors: Pagano Gianfranco , Cavallo-Perin Paolo , Cavalot Franco , Dall'Omo Anna Maria , Masciola Paola , Suriani Renzo , Amoroso Antonio , Curtoni Sergio Emilio , Borelli Iolanda , Lenti Gianfranco
Published: September 2013

The 1-yr incidence of insulin-dependent diabetes mellitus (IDDM) in a population of the Piedmont and Aosta Valley area of Italy was recorded. Anti-virus antibodies (e.g., Coxsackie B1-6, mumps, cytomegalovirus), islet cell antibodies (ICAs), and H LA-A, -B, -C, and -DR were determined in 74 IDDM patients (38 males, 36 females) and in controls. Total IDDM incidence was 5.0/100,000, and the incidence for those <20 yr of age was 11.6/100,000. Anti-virus antibody frequency was not different in IDDM patients and controls. ICAs were present in 58% of IDDM patients at onset and in 30% after 12 mo, and complement-fixing ICAs were found in 39 and 17%, respectively. IDDM was significantly and positively associated with DR3/DR4 and negatively associated with DR2 and DR5. ICA frequency was significantly higher in DR3/DR4 heterozygote patients than in patients without DR3 and DR4. These results suggest that in this IDDM population 1) viral etiology is not evident, 2) ICAs offer only a partial pathogenetic explanation, and 3) genetic and immunologic heterogeneity is evident.
High K+ Rapidly Stimulates Ca2+-Dependent Phosphorylation of Three Proteins Concomitant With Insulin Secretion From HIT Cells
Authors: Oberwetter James M , Boyd A E
Published: September 2013

We have previously shown in a glucose-responsive insulin-secreting β-cell line (HIT cells) that a cell membrane–depolarizing concentration of K+ causes an influx of extracellular Ca2+ that elevates the free cytosolic Ca2+ concentration ([Ca2+],) and activates insulin secretion. To identify the cellular mechanisms that couple Ca2+ influx to exocytosis, studies of protein phosphorylation were conducted. HIT cells were loaded with 32P and stimulated with either 40 mM K+ or 19.4 mM glucose, both of which trigger the immediate release of insulin. Phosphoproteins were examined with two-dimensional polyacrylamide gel electrophoresis and autoradiography. With addition of 40 mM K+, after the rise in [Ca2+]1 proteins of Mr 17,500, 20,000, and 24,000 were rapidly and specifically phosphorylated. The 17,000-Mr protein showed maximum phosphorylation by 1 min, whereas phosphorylation of the 24,000- and 20,000-Mr proteins continued to increase at 5 min. Despite stimulating the immediate release of insulin, high glucose did not result in a change in [Ca2+], or the phosphorylation of the three Ca2+-dependent phosphoproteins. Insulin secretion, the increase in [Ca2+]1, and phosphorylation of the proteins by 40 mM K+ was inhibited by 100 μM verapamil, an organic Ca2+-channel–blocking drug. The rapid phosphorylation of three proteins, after a rise in [Ca2+]1 and the coordinate inhibition of insulin secretion and phosphorylation, are consistent with the hypothesis that Ca2+ enters the β-cell through voltage-dependent Ca2+ channels, regulating insulin release by effects on protein phosphorylation. However, glucose activates the immediate release of insulin by another, as yet undefined, mechanism.
Influence of Lactation on Morphometric and Secretory Variables in Pancreatic β-Cell of Mildly Diabetic Rats
Authors: Marynissen Greta , Malaisse Willy J , Van Assche F Andre
Published: September 2013

In nondiabetic rats, lactation accelerates the restoration of pancreatic β-cell function after the period of increased secretory activity associated with pregnancy. To investigate whether a comparable situation prevails in mildly diabetic animals, streptozocin (22.5 mg/kg body wt) was administered to female rats at the onset of pregnancy. Plasma glucose and insulin concentrations, content and release of insulin in isolated islets, total mass and volume density of both the endocrine pancreas and granulated β-cells, and ultrastructural prevalence of light and dark secretory granules were measured on the 20th day of pregnancy and in lactating and nonlactating animals 20 days after delivery. In the mildly diabetic animals, the changes in endocrine pancreatic function normally associated with pregnancy and lactation were greatly attenuated, albeit not completely eliminated. We propose that the increased biosynthetic and secretory activity imposed on surviving β-cells after streptozocin administration tends to mask the adaptative changes in β-cell function otherwise seen during the postpartum and lactation period.
Glomerulopathy in Spontaneously Diabetic Rat: Impact of Glycemic Control
Authors: Cohen Andrew J , McGill Paul D , Rossetti Ronald G , Guberski Dennis L , Like Arthur A
Published: September 2013

The spontaneously diabetic BioBreeding/Worcester (BB/W) rat was used to examine the role of glycemie control in the pathogenesis of diabetic glomerulopathy and proteinuria. Nondiabetic BB/W rats (group 1) were compared with moderately (group 2) and severely (group 3) hyperglycemie diabetic animals of similar age. Urinary protein excretion and morphometric measurements of glomerular basement membrane (GBM) width and mesangial area were performed after 4, 8, and 12 mo of study.

At 4 mo, urinary protein excretion both in group 2 (9.3 ± 0.7 mg/24 h) and group 3 (24.8 ± 1.98 mg/24 h) exceeded that in group 1 (5.4 ± 0.6 mg/24 h; P < .05). Moreover, proteinuria in group 3 was significantly greater than in group 2 (P < .05). In addition, proteinuria increased in group 3 animals between 4 and 12 mo of study but did not advance in groups 1 or 2.

GBM width in both diabetic groups (168.8 ± 2.4 and 165.7 ± 2.2 nm, groups 2 and 3, respectively) exceeded that in group 1 (148.3 ± 3.8 nm; P < .01) by 4 mo. At 12 mo, severely hyperglycemie group 3 animals had significantly greater GBM thickening than group 2. GBM width increased in all three groups over the course of study, but the rate of growth did not differ between groups 1 and 2. However, the rate of growth in group 3 was greater than in either group 1 or group 2. Urinary protein excretion correlated significantly with GBM width in diabetic rats. No differences in proportional mesangial area or the proportional area made up of mesangial matrix or cytoplasm could be found among the three groups.

In the spontaneously diabetic BB/W rat, poor glycemie control contributes to both proteinuria and GBM widening but apparently does not cause mesangial expansion. Proteinuria and GBM widening may either be interdependent or related to a common third factor in the diabetic milieu.
Effect of Ascorbate and Dehydroascorbate on Tissue Uptake of Glucose
Authors: Mooradian Arshag D
Published: September 2013

In vitro studies have suggested that ascorbate or dehydroascorbate share with glucose the same tissue-transport carrier. To determine if ascorbic acid or its oxidized form can inhibit tissue uptake of glucose, the brain uptake index (BUI) and muscle uptake index of glucose were determined by single arterial injection tissue-sampling technique. The injectate was either buffered Ringer's solution with varying concentrations of ascorbate, dehydroascorbate (pH 7.4), or 70% serum from individuals on vitamin C supplements. Ascorbic acid over a wide range of concentrations (0–10,000 mg/L) did not reduce the BUI. Ascorbic acid reduced BUI from the control value of 33 ± 3.2 to 20.1 ± 2.2% (P < .01) only at 100,000 mg/L; this effect was probably secondary to osmotic disruption of blood-brain barrier. In contrast, dehydroascorbate inhibited the BUI of glucose from baseline value of 32.8 ± 1.1 to 10.7 ± 0.67%, with an estimated K, of 13.0 mM. Masseter muscle glucose uptake was not significantly altered over a wide range of ascorbate or dehydroascorbate concentrations in the injectate. Dehydroascorbate (7500 mg/L) did not significantly reduce the BUI of [14C]phenylalanine (55.2 ± 4.4 vs. 62.1 ± 4.2% in controls). When serum from six individuals on calcium ascorbate (3–5 g/day) was compared with that of nine controls, the BUI was not different (19.3 ± 1.7 vs. 19.3 ± 1.1%). Similarly, supplementing the diet of eight healthy volunteers with 1 g calcium ascorbate for 8 days did not alter the BUI of glucose. We conclude that dehydroascorbic acid, but not ascorbic acid, inhibits in vivo brain but not muscle uptake of glucose, suggesting a common carrier system at the level of the blood-brain barrier. The low serum levels of ascorbate even after vitamin C supplementation are not sufficient to impair brain glucose uptake.
Specificity of Monoclonal Anti-Human Insulin Antibodies
Authors: Storch Max-Jürgen , Licht Thomas , Petersen Karl-Georg , Obermeier Rainer , Kerp Lothar
Published: September 2013

To define the specificity and epitope of five monoclonal antibodies (MoAbs) to human insulin, binding studies with artificially modified insulins and a number of native insulins were done. Epitopes on the A-chain (A4, A8–A10) and on the end of the B-chain (B30) could be identified. For two MoAbs, substructures of the amino acid B30 were found, which were essential for binding (hydroxyl and methyl groups of B30). In contrast to most antisera, MoAbs to human insulin show high specificity. However, as the study shows, the specificity is not absolute. With suitable artificial epitope modifications, cross-reaction can be seen. Two of the MoAbs used here show sufficient specificity to discriminate between insulin and proinsulin.
Insulin Hyperpolarizes Rat Myotube Primary Culture Without Stimulating Glucose Uptake
Authors: Zierler Kenneth
Published: September 2013

Insulin (100 μU/ml) increased the electrical potential difference between the inside and outside of fused myotubes from fetal rat hindlimbs 5–8 days after primary culture. Myotubes were hyperpolarized by 3.5 ± 1.2 mV (mean ± SE). Tetrodotoxin (TTX) eliminated spontaneous twitching. With TTX, membrane potentials of myotubes became more negative both in the absence and presence of insulin, and insulin hyperpolarized myotubes by 6.6 ±1.7 mV, which is at least as great as the hyperpolarization this concentration of insulin produced in muscles excised from young adult rats. However, insulin did not significantly stimulate uptake of the glucose analogue 2-deoxy-D-glucose, although there was basal D-glucose transport. Specific insulin receptors were present, demonstrated by radioinsulin binding. In summary, in primary cultures of rat myotubes, there are insulin receptors, insulin hyperpolarizes at least as much as it hyperpolarizes muscle excised from young adult rats, but insulin does not stimulate D-glucose transport.
Insulin and Other Stimulants Have Nonparallel Translational Effects on Protein Synthesis
Authors: Okabayashi Yoshinori , Moessner Joachim , Logsdon Craig D , Goldfine Ira D , Williams John A
Published: September 2013

Isolated pancreatic acini from streptozocin-induced diabetic rats were used to study the role of insulin on the synthesis of specific cellular proteins. When acini were incubated with 0–100 nM insulin for 2 h and then pulsed with [35S]methionine, a dose-dependent increase in [35S]methionine incorporation into total cellular proteins was observed. When acinar cell lysates were subjected to gel electrophoresis, 12 major newly synthesized protein bands were resolved. Insulin (100 nM) increased the incorporation of [35S]methionine into all bands but with significantly different rates, varying from 84 to 216% of control. Next, specific antibodies to amylase, trypsin, ribonuclease, myosin, and lactate dehydrogenase (LDH) were used to evaluate the biosynthesis of known proteins. Insulin stimulated labeled amino acid incorporation into amylase by 148% over control. Insulin stimulated the synthesis of trypsinogen to a similar degree, but ribonuclease systhesis showed a significantly smaller increase of 53% over control. Insulin stimulated myosin and LDH synthesis by 169 and 184%, respectively. A differential pattern of protein synthesis was also observed when acini were treated with two other stimulators of protein synthesis, cholecystokinin and hemin. Both of these stimulators had a reduced effect on ribonuclease synthesis compared with amylase and trypsinogen synthesis but failed to increase myosin synthesis. When the RNAs extracted from control acini and acini treated with 100 nM insulin were translated in vitro, the proteins synthesized were quantitatively similar. This study therefore indicates that insulin has translational effects on acinar protein synthesis, and these effects are nonparallel for various specific acinar cell proteins.
Extended Survival of MHC-Compatible Islet Grafts From Diabetes-Resistant Donors in Spontaneously Diabetic BB/W Rat
Authors: Selawry Helena , Fojaco Rita , Whittington Karen
Published: September 2013

Transplantation of a large inoculum of incubated islets of MHC-compatible donors led to an extended survival of the grafts to an average of >86 days in 71% of male diabetic BB/W recipients. Identical results were obtained whether the immunologically privileged abdominal testis or the nonimmunologically favored renal subcapsular space was used as the organ site for the injection of the islets. Survival of the islet grafts was also independent of the duration of diabetes in the BB/W rats at the time of transplantation. These results showed that under our experimental conditions the grafted islets were able to become established and survive for extended periods in nonimmunosuppressed spontaneously diabetic BB/W hosts.
Six-Month Treatment with Sorbinil in Asymptomatic Diabetic Neuropathy: Failure to Improve Abnormal Nerve Function
Authors: Martyn Christopher N , Reid William , Young Robert J , Ewing David J , Clarke Basil F
Published: September 2013

The effect of long-term treatment with the aldose reductase inhibitor sorbinil (125 mg daily for 6 mo) was examined in 22 diabetic patients with subclinical abnormalities of nerve function. This was a placebo-controlled, double-blind crossover trial in which each of the two treatment periods lasted 6 mo. Peripheral nerve function was assessed electrophysiologically and by quantitative sensory testing; autonomie function was assessed by measurement of five cardiovascular reflexes and of mean heart rate from a 24-h ECG recording. Measurement of erythrocyte sorbitol concentrations demonstrated very significant inhibition of aldose reductase activity with sorbinil treatment, but no concomitant improvement in either peripheral or autonomie nerve function was observed.
Low-Dose Streptozocin-Induced Diabetes in Mice: Electron Microscopy Reveals Single-Cell Insulitis Before Diabetes Onset
Authors: Kolb-Bachofen Victoria , Epstein Stefan , Kiesel Ulrich , Kolb Hubert
Published: September 2013

We investigated the morphology of mouse islets 5 days after completion of low-dose streptozocin treatment of C57BL/6 mice by electron microscopy. At this stage, mice were still normoglycemic and light microscopy did not reveal massive islet infiltration. The electron-microscopic investigation revealed two characteristics indicative of ongoing islet cell destruction. In all islets investigated, lysed islet β-cells were recognized by disrupted plasma membranes and concomitantly decreased plasma contrast. Many of the lysed islet β-cells still contained numerous insulin granules. We also found immunocytes scattered throughout the islets, most of which could be identified as macrophages. Some were found engaged in phagocytosis of islet β-cell debris. This early stage of islet lesion termed single-cell insulitis is followed by the well-known later stage of massive infiltration easily recognized in light microscopy. Administration of silica particles to mice treated with low-dose streptozocin inhibited macrophage infiltration of islets as shown by immunocytochemistry with macrophage-specific monoclonal antibody F4/80. In parallel, the development of hyperglycemia was suppressed. The observations favor a pathogenic role of macrophages in islet destruction.
Rapid Reduction and Return of Surface Insulin Receptors After Exposure to Brief Pulses of Insulin in Perifused Rat Hepatocytes
Authors: Goodner Charles J , Sweet Ian R , Harrison H Courtenay
Published: September 2013

Hepatic receptors are normally exposed to discrete pulses of insulin and glucagon at intervals of 8 to 16 min. Using a multicolumn system for perifusing hepatocytes, we investigated the effect of this pattern on the normal processing of the insulin receptor. Surface-receptor binding was measured in acid-washed cells harvested from individual columns. The number of high-affinity surface receptors fell to a nadir 1 min after the end of a 3-min square-wave pulse of insulin. The maximum reduction reached 45% of baseline at amplitudes of 1000 μU/ml or above. The number of surface binding sites returned to baseline 15 min after the end of the pulse, but the affinity constant of the high-affinity receptor was unchanged. The reduction of surface binding was dose dependent, with an ED50, of 251 ± 34 μU/ml. Prolonging the pulse to 60 min did not affect the nadir or the rate of restoration of the surface-receptor population. The change in surface binding was reduced at 15°C and abolished at 4°C. After a pulse, the pattern of change was a period of rapid decline to a nadir (t1/2 ≤ 1 min) that persisted for 3–5 min, followed by restoration of surface binding that reached baseline in 10–15 min. This same pattern was present after six ED95 pulses delivered at intervals of 15 min. These data indicate that the internalization of hepatocyte surface receptors and their recycling and reinsertion into the plasma membrane can be entrained to pulses at the physiologic pulse frequency.
Undersulfation of Glomerular Basement Membrane Heparan Sulfate in Experimental Diabetes and Lack of Correction With Aldose Reductase Inhibition
Authors: Cohen Margo Panush , Klepser Henry , Wu Van-Yu
Published: September 2013

In this study we examined the effect of experimental diabetes and of treatment with an aldose reductase inhibitor on the level of sulfation of glomerular basement membrane (GBM) heparan sulfate, the principal glycosaminoglycan in this extracellular matrix. Glycosaminoglycans were isolated from GBM purified from control, streptozocin-induced diabetic, and sorbinil-treated diabetic rats and analyzed for sulfate and uronate content. Glomerular yields from diabetic kidneys were greater than those from control animals, but the amount of sulfate per glomerulus in diabetic samples, both untreated and sorbinil treated, did not differ significantly from that in control samples. However, the sulfate-to-uronate ratio in heparan sulfate isolated from diabetic GBM (0.34 ± 0.08) was significantly less than in control samples (0.69 ± 0.11), and treatment of diabetic rats with an aldose reductase inhibitor did not correct this reduced ratio (0.36 ± 0.06). The results indicate that there is an undersulfation of heparan sulfate of GBM in experimental diabetes, an abnormality that may contribute to loss of anionie sites and decreased charge selectivity of the glomerular filtration barrier. The findings further suggest that this abnormality results from disturbances in glycosaminoglycan synthesis and/or metabolism in diabetes that are independent of polyol-pathway activation in the renal glomerulus.
Effect of L-Carnitine Treatment on Lipid Metabolism and Cardiac Performance in Chronically Diabetic Rats
Authors: Rodrigues Brian , Xiang Hong , McNeill John H
Published: September 2013

The beneficial effects of L-carnitine administration were studied in vivo in isolated perfused working hearts from control and diabetic rats. Control and streptozocin-induced diabetic (STZ-D) rats were treated daily for 6 wk with high-dose L-carnitine (3 g · kg−1 · day−1 i.p.). STZ-D results in loss of body weight and hypoinsulinemia. These effects were not altered by L-carnitine treatment. Myocardial free-carnitine levels were decreased in the untreated diabetic rats. L-Carnitine treatment of the diabetic rats increased myocardial free-carnitine levels, which were comparable with those of control rats. Six weeks after STZ administration, hearts from untreated diabetic animals exhibited depressed left ventricular developed pressure, cardiac contractility, and ventricular relaxation rates compared with control animals. However, this depression was not seen in the L-carnitine-treated diabetic animals. L-Carnitine treatment of diabetic rats significantly reduced plasma glucose and lipid levels but had no effect on control rats. Furthermore, thyroid hormone levels were higher in the L-carnitine-treated diabetic rats than in the untreated diabetic group. The data suggest that high-dose L-carnitine treatment may reduce the severity of diabetes and result in improved cardiac performance.
Exogenous Arachidonic Acid Promotes Insulin Release From Intact or Permeabilized Rat Islets by Dual Mechanisms: Putative Activation of Ca2+ Mobilization and Protein Kinase C
Authors: Metz Stewart A
Published: September 2013

A number of indirect studies suggest a role for endogenous arachidonic acid (AA) in pancreatic islet function. To probe the effects of this fatty acid, AA and other polyunsaturated fatty acids were exogenously provided in Ca2+-free medium to avoid the formation of insoluble or impermeant Ca2+-arachidonate complexes. Concentrations of AA of ≧3 μM induced potent and sustained but reversible 45Ca efflux from prelabeled intact (or digitonin-permeabilized) islets; AA also nduced insulin release at somewhat higher concentrations. Other unsaturated fatty acids (erucic, oleic, linoleic, linolenic, dihomo-γ-linolenic, eicosapentaenoic, docosahexaenoic acids) were generally less active than AA itself, indicating a structure-function relationship. The effects of AA were saturable, were inhibitable by cooling, and were not accompanied in parallel by 51Cr release or trypan blue retention, suggesting a nontoxic mechanism. At low concentrations (3.3–16 μM), at which AA does not stimulate insulin release, AA-induced 45Ca efflux was not reduced by pretreatment with ionomycin (to deplete membrane-bound Ca2+ stores), suggesting stimulation of Ca2+ extrusion through the plasma membrane. At higher concentrations (≧25 μM), at which AA promotes insulin release, further Ca2+ efflux was stimulated, which was blunted by pretreatment with ionomycin (as well as by trifluoperazine). Conversely, pretreatment with AA obliterated the effects of ionomycin (3 μM) on cellular Ca2+ mobilization. Thus, AA also mobilizes Ca2+ from intracellular organelles, leading to a rise in free cytosolic Ca2+ (as previously reported). AA-induced 45Ca efflux and insulin release were independent of the presence of extracellular Na+ and did not require the oxygenation of AA. Dose-response curves comparing45Ca efflux and insulin secretion suggested that AA also stimulates hormone release by at least one other mechanism in addition to Ca2+ mobilization. This second stimulatory effect of AA could be seen in digitonin-permeabilized islets, where changes in cytosolic free Ca2+ concentration were vitiated by EGTA-containing buffers. Such secretion was also saturable and was inhibited by cooling or by spermine (which inhibits protein kinase C in the islet). Furthermore, AA-induced secretion from either intact or permeabilized islets was blunted by prolonged pretreatment of islets with a phorbol ester to deplete them of protein kinase C. Thus, exogenous arachidonic acid seems to be a complete secretagogue, having stimulatory effects both on Ca2+ mobilization and Ca2+-related secretory processes, putatively the activation of protein kinase C.
Clarification of Signaling Pathways Mediated by Insulin and Insulin-Like Growth Factor I Receptors in Fibroblasts From Patients With Specific Defect in Insulin Receptor
Authors: Sasaoka Toshiyasu , Kobayashi Masashi , Takata Yasumitsu , Ishibashi Osamu , Iwasaki Makoto , Shigeta Yukio , Goji Katsumi , Hisatomi Akitaka
Published: September 2013

Receptor binding and biological action of insulin and insulin-like growth factor I (IGF-I) were studied in fibroblasts from a patient with leprechaunism and a patient with type A syndrome of insulin resistance. Insulin binding was reduced to 18.8 and 27.7% of control value, respectively. In contrast, IGF-I binding was normal in both patients. In competitive binding studies, IGF-I had 0.2% of the ability of insulin to compete with 125I-labeled insulin binding, and insulin had 0.1% of the ability of IGF-I to compete with 125I-labeled IGF-I binding in control subjects and patient fibroblasts. The dose-response curves of insulin stimulation assessed by glucose incorporation and α-aminoisobutyric acid uptake showed normal responsiveness, and ED50 was significantly shifted to the right in fibroblasts from both patients. However, normal responsiveness and sensitivity were observed in thymidine incorporation studies. For IGF-I, dose-response curves of glucose incorporation, a-aminoisobutyric acid uptake, and thymidine incorporation were all normal in both patients. These results indicate that 1) the defect is specific to the insulin-receptor binding in these patients, 2) insulin and IGF-I activate glucose incorporation and α-aminoisobutyric acid uptake mainly through their own specific receptors, but 3) the IGF-I receptor appears to have a more important role in stimulating thymidine incorporation than the insulin receptor in physiological condition or, alternatively, an unknown postreceptor process with cascade signal transmission may overcome the decreased insulin-receptor binding to produce a normal dose-response curve.
Effect of myo-Inositol and T3 on Myocardial Lipids and Cardiac Function in Streptozocin-Induced Diabetic Rats
Authors: Xiang Hong , Heyliger Clayton E , McNeill John H
Published: September 2013

Numerous experimental studies have implied a link between diabetes-induced abnormal lipid buildup in the myocardium and the development of cardiomyopathy. Because the diabetic state in rats is associated with lowered T3 (triiodothyronine) and T4 levels and because diabetic patients excrete large amounts of myo-inositol, a lipotropic agent, we investigated the effects of myo-inositol and T3 on the elevated myocardial lipid levels and depressed cardiac performance of streptozocin (55 mg/kg i.v.)-induced diabetic (STZ-D) rats, myo-inositol (2.5 g kg−1 day−1 in the drinking water) and T3 (30 μg · kg−1 · day−1 s.c.) were given for an 8-wk period 3 days after diabetes induction. Untreated diabetic rats were characterized by a decreased rate of body weight gain, hyperglycemia, and hypoinsulinemia, which were not altered after myo-inositol and/or T3 treatment. Thyroid status of diabetic animals was normalized by T3 alone or in combination with myo-inositol but not by myo-inositol alone. The elevations in plasma and myocardial lipids associated with the diabetic state were prevented by myo-inositol treatment. However, the plasma lipid and myocardial cholesterol levels in diabetic rats remained elevated or were further increased with treatment with T3 or myo-inositol plus T3. myo-inositol treatment partially improved cardiac performance in STZ-D rats. T3 treatment alone did not prevent cardiac dysfunction in diabetic rats. There was, however, some improvement in heart function in the groups treated with both myo-inositol and T3, coinciding with a significant decrease in the myocardial triacylglycerol level. The data indicate that a possible correlation may exist between elevated myocardial triacylglycerol levels and cardiac dysfunction in diabetic rats.
Effect of Fish Oil Concentrate on Lipoprotein Composition in NIDDM
Authors: Schectman Gordon , Kaul Sushma , Kissebah Ahmed H
Published: September 2013

Non-insulin-dependent diabetes mellitus (NIDDM) is associated with elevated very-low-density lipoprotein (VLDL) triglyceride concentrations and abnormalities of low-density lipoprotein (LDL) composition. Because fish oil supplementation may favorably affect lipid and lipoprotein concentrations in nondiabetic subjects, we determined the effect of fish oil concentrate on plasma lipids and lipoprotein composition in patients with NIDDM. Dietary-supplementation 1-mo periods of 4.0 and 7.5 g of omega-3 fatty acids in fish oil were compared with a placebo of 12 g safflower oil by use of a single-blind crossover design. Medications, including antidiabetic therapy, were continued through the study. Compared with safflower oil treatment, fish oil supplementation resulted in a significant reduction of total plasma triglycerides of 24% at the 4-g doseand a larger reduction of 39% at the 7.5-g dose. These decreases were due to similar reductions in VLDL triglycerides. LDL cholesterol levels were mildly elevated, but a larger 20% increase in LDL apolipoprotein B (apoB) concentration was observed. During supplementation with the fish oil concentrate, the LDL cholesterol-to-apoB ratio was significantly reduced when compared with pretreatment values, but not when compared with safflower oil treatment. Highdensity lipoprotein (HDL) cholesterol and plasma apoA1 levels were not significantly changed during fish oil treatment. At the 7.5-g dose, fasting glucose and glycohemoglobin levels increased by 20 and 12%, respectively, but were unchanged at the lower level of supplementation. Thus, in NIDDM patients, dietary supplementation with omega-3 fatty acids induces a reduction in total plasma and VLDL triglyceride levels. However, the observed increase in LDL apoB levels, and the deterioration in glycemic control, indicate thatfurther study will be required to establish whether fish oil has a role in the treatment of NIDDM.
Glucose Counterregulation and Its Impact on Diabetes Mellitus
Authors: Gerich John E
Published: September 2013

Glucose counterregulation is the sum of processes that protect against development of hypoglycemia and that restore euglycemia if hypoglycemia should occur. In order of importance, the key counterregulatory factors are glucagon, epinephrine, growth hormone, cortisol, and hepatic autoregulation. These act primarily by increasing hepatic glucose output, initially via breakdown of glycogen and later by gluconeogenesis. In people without diabetes and in people with type II (non-insulin-dependent) diabetes, suppression of endogenous insulin secretion during hypoglycemia is also important in permitting full expression of the effects of counterregulation. People with diabetes are more prone to develop hypoglycemia for various reasons (e.g., insulin overdose, skipped meals, and intensive exercise); one that has recently been identified is impaired glucose counterregulation: patients with type I (insulin-dependent) diabetes (and to a lesser extent, patients with type II diabetes) lose the glucagon response to hypoglycemia; subsequent development of autonomic neuropathy with concomitant loss of the epinephrine response leads to almost complete paralysis of counterregulation and loss of recognition of hypoglycemia. To make matters worse, an episode of hypoglycemia that causes activation of counterregulation can lead to rebound hyperglycemia (Somogyi phenomenon); if this is improperly treated, brittle diabetes may follow. Thus, abnormalities in glucose counterregulation may predispose to severe hypoglycemia and prevent achievement of optimal glycemic control in patients with diabetes.
Expression of Peptide Hormone Genes in Human Islet Cell Tumors
Authors: Philippe Jacques , Powers Alvin C , Mojsov Svetlana , Drucker Daniel J , Comi Richard , Habener Joel F
Published: September 2013

The embryogenesis of the pancreas suggests the existence of a common stem cell progenitor of the four islet cell types (insulin, glucagon, somatostatin, and pancreatic polypeptide). We investigated whether neoplastic islet tumors express multiple hormonespecific cellular phenotypes of the islets. By analyses of RNA transcripts and immunoreactive peptides in four human insulinomas and one glucagonoma, we found that the insulin, somatostatin, and glucagon genes were coexpressed in all tumors. The expression of the three hormone genes in a lymph node metastasis of a glucagonoma reduced the possibility that contamination of tumor tissue by normal islets occurred. These observations lend further support to the hypothesis of the multipotentiality of neoplastic islet cells for the expression of genes encoding several different islet hormones.
Effect of Rapid Normalization of Plasma Glucose Levels on Microvascular Dysfunction and Polyol Metabolism in Diabetic Rats
Authors: Rogers Douglas , Rowold Edwin , Chang Katherine , Tomlinson Martha , Sherman William R , Gavin James , Kilo Charles , Williamson Joseph R
Published: September 2013

Effects of rapid normalization of plasma glucose levels (by insulin infused via Alzet pumps implanted intraperitoneally) on plasma insulin-like growth factor I (IGF-I) levels, granulation tissue polyol levels, and vascular permeation by 125I-labeled albumin were examined in male Sprague-Dawley rats with streptozocin-induced (60–65 mg/kg) diabetes. Two days after implantation of pumps, plasma insulin levels were twice normal levels and remained elevated (1.4–2.5 times normal) throughout the remainder of the study. Plasma glucose levels and granulation tissue polyol levels were normalized within 2 days after initiation of insulin treatment. Plasma IGF-I levels were significantly increased (2 times) by 2 days, but were not normalized until 7 days. In contrast, 125I-albumin permeation normalized at a much slower relatively linear rate and was still not completely normal after 14 days of insulin treatment. In view of 1) previous studies demonstrating that diabetes-induced increases in 125I-albumin permeation in this tissue are linked to increased metabolism of glucose to sorbitol and 2) the rapid normalization of tissue polyol levels in this study, the relatively linear rate of normalization of vascular permeability over 14 days in these studies suggests that impaired vascular barrier functional integrity in this model is mediated by structural and/or functional vascular alterations associated with sustained increased polyol metabolism rather than by increased polyol levels per se and/or by readily reversible functional and metabolic alterations associated with acute increases in polyol metabolism. The relatively long lag time after normalization of plasma glucose and tissue polyol levels before near normalization of vascular permeability in this model isconsistent with corresponding observations on the relationship between improved glycemic control and normalization of microangiopathy and neuropathy in diabetic humans and animals. The slow relatively linear rate of normalization of vascular permeability after normalization of plasma insulin and glucose levels and tissue polyol levels suggests that normalization of impaired vascular barrier function in this model is accomplished by a repair process (probably involving turnover of altered vascular constituents), the precise nature of which remains to be elucidated.
Phospholipid Metabolism and Protein Phosphorylation in Sciatic Nerve From Genetically Diabetic (db/db) Mouse
Authors: Berti-Mattera Liliana N , Eichberg Joseph
Published: September 2013

The incorporation of [32P]orthophosphate into phospholipids and proteins of sciatic nerve from genetically diabetic (db/db) and littermate control (db/m) C57BL/KsJ mice was studied. Nerves from animals of ages 12,16, 22, 26, and 38 wk were incubated in vitro. Among phospholipids, the uptake of isotope into phosphatidic acid was higher at nearly all ages examined. Phosphorylation of several proteins, including the major myelin glycoprotein, P0, and the small myelin basic proteins P, + P2, was significantly enhanced in nerves from both 12- and 38-wk-old diabetic mice. The altered pattern of protein phosphorylation, but not that of phospholipid metabolism, was similar to changes observed in sciatic nerve from streptozocin-induced diabetic rats. The relationship of the results to reported levels of myo-inositol, sorbitol, and Na+-K+-ATPase activity and to functional abnormalities in nerves of db/db mice is discussed. The findings suggest that caution should be exercised in reaching conclusions concerning which biochemical alterations observed in different animal models of diabetic neuropathy are invariably associated with the development of this disorder.