bluuebunny/crossref_metadata_2025 huggingface dataset:
Downregulation of Blood-Brain Barrier Glucose Transporter in Experimental Diabetes
Authors: Pardridge William M , Triguero Domingo , Farrell Christine R
Published: September 2013

Previous studies showing downregulation of bloodbrain barrier (BBB) glucose-transporter activity in vivo in experimental diabetes have recently been questioned. Therefore, our investigations examined both the BBB glucose-transporter activity in experimental diabetes in vivo, with the use of the in situ internal carotid artery perfusion technique, and the microvessel glucose-transporter concentration, with quantitative Western immunoblots. These studies show that BBB glucose-transporter activity in vivo is decreased 44% in experimental diabetes (blood glucose concn 443 ± 12 mg/dl), parallel with a 44% decrease in cerebral blood flow, a normal brain blood volume, and a 75% prolongation of capillary transit time. The glucose-transporter concentration is decreased 77 ± 9% in microvessels isolated from diabetic rat brain compared with controls, as measured by quantitative Western blotting. These studies confirm the original observations that the BBB glucose transporter is downregulated in experimental diabetes, in association with a parallel decrease in cerebral blood flow. In addition, these studies, in conjunction with other recent experiments from this laboratory showing elevated glucose-transporter mRNA in diabetic rat brain capillaries, suggest the primary mechanism underlying the downregulation is a posttranscriptional inhibition of glucose-transporter mRNA translation.
Glomerular Structure and Function in Diabetic Nephropathy: Early to Advanced Stages
Authors: Østerby Ruth , Parving Hans-Henrik , Hommel Eva , Jørgensen Hans E , Løkkegaard Hans
Published: September 2013

Kidney biopsies from 14 insulin-dependent diabetes mellitus patients with persistent albuminuria were studied by light and electron microscopy. In terms of kidney function, the patients spanned stages from early to advanced nephropathy. The clinical parameters were (ranges, with medians in parentheses) urinary albumin excretion (UAE) 158–5494 μg/min (1153 μg/min), glomerular filtration rate (GFR) 30–128 ml · min −1 · 1.73 m−2 (90 mh ml · min−1 · 1.73 m−2) and mean arterial blood pressure () 87–122 mmHg (109 mmHg). The severity of clinical nephropathy (UAE, GFR, and BP together) correlated with an index of the structural lesions (basement membrane [BM] thickness, mesangial expansion, and glomerular occlusion together; r = 0.62, 2P < 0.05). GFR compared with remnant surface of glomerular capillaries (filtration surface; FS) gave values of r = 0.72 and 2P = 0.004, and UAE compared with the percentage of the peripheral BM surface carrying fluffy loose intrinsic fine structure gave r = 0.62 and 2P = 0.02. BP per se did not correlate with structural parameters. The area of FS per open glomerulus did not decrease with increasing mesangial volume fraction, which indicates compensatory changes of the capillaries in early and advanced stages of glomerulopathy. In 7 patients with <10% occluded glomeruli, correlations between glomerular volume and the parameters of diabetic glomerulopathy (i.e., BM thickness and volume fractions of mesangium and mesangial matrix) failed to reach statistical significance. The actual glomerular volume, however, is a product of the individual's original glomerular volume, probably the early diabetic hypertrophy and modifying changes consequent to the development of glomerulopathy. Our study shows a correlation between the parameters of glomerular structural lesions and those of the functional abnormalities in diabetic nephropathy.
Effect of Insulin on Glucose Utilization in Epitrochlearis Muscle of Rats With Streptozocin-Induced NIDDM
Authors: Karl Irene E , Gavin James R , Levy Joseph
Published: September 2013

Because skeletal muscle plays a major role in glucose disposal, it may be the primary site of insulin resistance in non-insulin-dependent diabetes mellitus (NIDDM). Rates of glycogen synthesis (GS), glucose utilization via glycolysis, glycolytic utilization (GU), and glucose transport (GT) were studied in epitrochlearis muscles (EMs) obtained from 10-wk-old nonfasted Sprague-Dawley rats in which NIDDM was neonatally induced with streptozocin. Plasma glucose in NIDDM rats was elevated (P < 0.001), whereas plasma insulin was similar in NIDDM and control rats. No differences in muscle weight, protein, glycogen, ATP, phosphocreatine, lactate, lactate-pyruvate ratios, or glucose-6-phosphate were noted in EMs of control and NIDDM rats. EMs were incubated in medium containing 5.6 or 11.2 mM glucose with tracer D-[5-3H]glucose and insulin from 0 to 7.18 × 10−7 M for 1 or 2 h, and GS, GT, and GU were evaluated. Similar rates of basal (non-insulin-mediated) and insulin-stimulated GS, GU, and GT were observed in EMs of NIDDM and control rats incubated in 5.6 mM glucose for 2 h. Insulin doseresponse curves revealed similar sensitivities and responsiveness. Increasing glucose concentration (from 5.6 to 11.2 mM) induced significant increases in basal rates of GS, GU, and GT in EMs of control but not NIDDM rats. Insulin dose-response curves for GS and GT revealed decreased sensitivity and no change in responsiveness in EMs of control and NIDDM rats, even though GU of EMs of NIDDM rats was significantly lower at basal and all other insulin concentrations. These data revealed that both insulin resistance and glucose resistance contribute to the impaired glucose metabolism in EMs of the NIDDM rat.
Amount and Speed of Fast Axonal Transport in Diabetes
Authors: Abbate Samuel L , Atkinson Mark B , Breuer Anthony C
Published: September 2013

Abnormalities in axonal transport have been observed in human and experimental diabetes and may be related to the pathogenesis of diabetic neuropathy. Axonal transport has previously been evaluated by indirect methods. In this study, direct-measurement techniques were applied (with computer-enhanced video-recorded images) for the first time to evaluate intra-axonal organelle speed and frequency (the amount of organelle traffic) in both the anterograde fast component (AFC) and retrograde fast component (RFC) of axonal transport in diabetic nerve. Sciatic nerve and dorsal and ventral nerve roots were studied in the animal model of insulin-dependent diabetes (BB/Wistar rat) and sciatic nerve in the non-insulin-dependent (streptozocin-induced) model of diabetes (STZ-D rat). STZ-D rats were studied at 1 mo, and BB/Wistar rats were studied at 1 and 2 mo of diabetes duration. Statistically significant decreases in peripheral axon organelle speed were found only for RFC at 1 mo of diabetes in both the BB/Wistar (8.1%) and STZ-D (5.4%) rats. The difference was no longer significant in BB/Wistar rats at 2 mo of diabetes. This recovery suggests that the underlying abnormality is reversible. No differences were seen in AFC of any axons, and the only other difference seen was a 5.1% decrement in RFC at 2 mo in the ventral roots. No significant difference was observed in any group for organelle frequencies. Other factors should be considered to explain the decrease in materials transported in accumulation studies. The transient deficits in RFC speed observed remain of undetermined significance in the pathogenesis of diabetic neuropathy.
Low Sex-Hormone-Binding Globulin Concentration as Independent Risk Factor for Development of NIDDM: 12-Yr Follow-Up of Population Study of Women in Gothenburg, Sweden
Authors: Lindstedt Göran , Lundberg Per-Arne , Lapidus Leif , Lundgren Hans , Bengtsson Calle , Björntorp Per
Published: September 2013

Serum sex-hormone-binding globulin (SHBG) and corticosteroid-binding globulin (CBG) concentrations were evaluated as risk factors for the development of non-insulin-dependent diabetes mellitus (NIDDM), myocardial infarction, stroke, and premature death in a prospective study of 1462 randomly selected women, aged 38–60 yr, over 12 yr of observation. In multivariate analysis, taking only age into consideration as a confounding factor, low initial concentration of SHBG was significantly correlated to the incidence of NIDDM and stroke, and high initial concentration of CBG was correlated to the incidence of NIDDM. There were also significant correlations between SHBG and CBG concentrations on one hand and possible risk factors for the end points studied, such as serum triglycerides, serum cholesterol, fasting blood glucose, body mass, body mass index, waist/hip ratio, smoking habits, and systolic blood pressure, on the other. When these possible confounders, in addition to age, were taken into consideration in multivariate analyses, only the inverse significant correlation between SHBG and NIDDM remained. The increased incidence of diabetes was confined to the lowest quintile of SHBG values, where it was 5-fold higher than in the remaining group. This incidence was further increased to 8- and 11-fold in the lowest 10 and 5% of the values, respectively. We conclude that SHBG is a uniquely strong independent risk factor for the development of NIDDM in women.
Differential Effects of Prednisone and Growth Hormone on Fuel Metabolism and Insulin Antagonism in Humans
Authors: Horber Fritz F , Marsh H Michael , Haymond Morey W
Published: September 2013

Human growth hormone (hGH) and prednisone cause insulin resistance and glucose intolerance. However, it is unknown whether hGH and prednisone antagonize insulin action on protein, fat, and carbohydrate metabolism by a common or independent mechanism. Therefore, protein, fat, and carbohydrate metabolism was assessed simultaneously in four groups of eight subjects each after 7 days of placebo, recombinant DNA hGH (rhGH; 0.1 mg · kg−1 · day−1), prednisone (0.8 mg · kg−1 · day−1), or rhGH and prednisone administration after an 18-h fast and during gut infusion of glucose and amino acids (fed state). Fasting plasma glucose concentrations were similar during placebo and rhGH but elevated (P < 0.001) during combined treatment, whereas plasma insulin concentrations were higher (237 ± 57 pmol/ml, P < 0.001) during combined than during placebo, rhGH, or prednisone treatment (34, 52, and 91 pM, respectively). In the fed state, plasma glucose concentrations were elevated only during combined treatment (11.3 ± 2.1 mM, P < 0.001). Plasma insulin concentrations were elevated during therapy with prednisone alone and rhGH alone (667 ± 72 and 564 ± 65 pmol/ml, respectively, P < 0.001) compared with placebo (226 ± 44 pmol/ml) but lower than with the combined rhGH and prednisone treatment (1249 ± 54 pmol/ml, P < 0.01). Protein oxidation ([14C]leucine) increased (P < 0.001) with prednisone therapy, decreased (P < 0.001) with rhGH treatment, and was normal during the combined treatment. By indirect calorimetry, glucose oxidation was similar in all groups; fasting fat oxidation was decreased by prednisone (P < 0.001) and increased by rhGH, although only significantly in the fed state (P < 0.01). In summary, insulin antagonism of rhGH and prednisone are probably caused by independent mechanisms in which rhGH and prednisone may reciprocally regulate the oxidation of protein and fat while decreasing the efficiency of glucose disposal.
Effects of Fetal Insulin Deficiency on Growth in Fetal Lambs
Authors: Philipps Anthony F , Rosenkrantz Ted S , Clark Richard M , Knox Isabella , Chaffin David G , Raye John R
Published: September 2013

Insulin may be an important regulator of growth in late fetal life. To assess the importance of endogenous insulin release in regulation of normal fetal growth, eight fetal lamb pairs were given either an intravenous injection of streptozocin (STZ), a nitrosourea that selectively damages pancreatic β-cells, or buffer infusion (controls). In six preparations, twins were used, and in two cases, triplets, thus allowing for comparison between treated and control fetuses residing in the same intrauterine environment. Fetal STZ injection was associated with relative fetal hyperglycemia, hypoinsulinemia, and a decrease in the fetal plasma insulin-glucose ratio. Fetal lambs exposed to STZ also developed a mild nonprogressive metabolic acidosis compared with controls. Fetal body weight was depressed by 21% overall, the magnitude of reduction related to length of time in utero after STZ injection. Similar reductions in organ weights (liver, heart, and kidney) were also observed in STZ-administered fetuses compared with controls. Protein accretion in carcass, liver, and kidney after STZ was also depressed, but no significant changes in fetal lipid accretion were observed. Skeletal growth, as measured by tail and tibial lengths, was also depressed after STZ but to a lesser extent than body weight or protein accretion. Thus, in a stable maternal environment, isolated fetal insulin deficiency is associated with significant retardation of somatic and skeletal growth and protein deposition.
Contribution to Postprandial Hyperglycemia and Effect on Initial Splanchnic Glucose Clearance of Hepatic Glucose Cycling in Glucose-Intolerant or NIDDM Patients
Authors: Butler Peter C , Rizza Robert A
Published: September 2013

Excessive amounts of glucose enter the systemic circulation when patients with non-insulin-dependent diabetes mellitus (NIDDM) eat a carbohydrate-containing meal. To determine the contribution of hepatic glucose cycling (defined as the net effect of glucose/glucose-6-phosphate cycling and uptake and release of glucose from hepatic glycogen) to postprandial hyperglycemia, diabetic, glucose-intolerant, and nondiabetic subjects were fed mixed meals. The meal contained both [2-3H]glucose (an isotope that is extensively detritiated during hepatic glucose cycling) and [6-3H]glucose (an isotope that is not detritiated during hepatic glucose cycling). Of the 50 g of carbohydrate contained in the meal, ∼4–8 g underwent hepatic glucose cycling. Although total cycling of ingested glucose did not differ between diabetic, glucose-intolerant, and nondiabetic subjects (361 ± 67 vs. 494 ± 106 vs. 322 ± 44 μmol · kg−1 · 5 h−1, respectively), the data suggested that hepatic cycling was increased in the diabetic and glucose-intolerant individuals but not in the nondiabetic subjects during the first 2 h after eating. Hepatic cycling during the first 2 h after eating was correlated with the prevailing glucagon concentration (r = 0.6, P < 0.01) and increased (P < 0.05) as hepatic glucose release increased. Hepatic glucose cycling had a marked effect on the measurement of so-called initial splanchnic glucose uptake. Nevertheless, however measured, initial splanchnic glucose uptake was not decreased and, if anything, was increased in diabetic and glucose-intolerant patients. Integrated postprandial hepatic glucose release increased (r < 0.01) with the severity of fasting hyperglycemia. These results indicate that postprandial hyperglycemia in diabetic and glucose-intolerant patients is not due to enhanced hepatic glucose cycling or a lack of uptake of ingested glucose by the splanchnic bed but rather to excessive release of glucose by the liver coupled with a failure of extrahepatic tissues to appropriately increase glucose disposal.
Chronology and Determinants of Tissue Repair in Diabetic Lower-Extremity Ulcers
Authors: Pecoraro Roger E , Ahroni Jessie H , Boyko Edward J , Stensel Victoria L
Published: September 2013

The natural history of tissue repair and the critical determinants of faulty healing of diabetic ulcers remain obscure despite recent advances in our knowledge of the cellular physiology of normal cutaneous healing. To characterize the chronology and identify important factors affecting healing, we applied an objective method to quantify the rate of wound healing of full-thickness lower-extremity ulcers in 46 diabetic outpatients who received local wound care under a standardized clinical protocol. The initial ulcer healing rate, eventual status of tissue repair, and definitive clinical outcome were not significantly associated with age; diabetes type, duration, or treatment; level or change in glycosylated hemoglobin; current smoking; presence of sensory neuropathy; ulcer location or class; initial infection; or frequency of recurrent infections. However, direct measures of local cutaneous perfusion, estimated by periwound measurements of transcutaneous O2 tension (TcPo2) and transcutaneous CO2 tension (TcPco2), were significantly associated with the initial rate of tissue repair (P = 0.003 and 0.005, respectively). The strong prediction of early healing by these parameters of local skin perfusion was independent from the effects of segmental Doppler arterial blood pressure at the dorsalis pedis, although eventual ulcer reepithelialization was significantly related to foot blood pressure and periwound TcPo2 and TcPco2. We conclude that periwound cutaneous perfusion is the critical physiological determinant of diabetic ulcer healing, indicating a 39-fold increased risk of early healing failure when the average periwound TcPo2 is <20 mmHg.
Retardation by Aminoguanidine of Development of Albuminuria, Mesangial Expansion, and Tissue Fluorescence in Streptozocin-Induced Diabetic Rat
Authors: Soulis-Liparota Tina , Cooper Mark , Papazoglou Dimitria , Clarke Belinda , Jerums George
Published: September 2013

This study evaluated the relationship between the development of fluorescence related to advanced glycosylation end products (AGEs) in the kidney and experimental diabetic nephropathy over a 32-wk period. Control, untreated diabetic, and aminoguanidine-treated diabetic rats were followed for 32 wk with eight weekly measurements of urinary albumin excretion. After 32 wk, collagen-related fluorescence in aorta and kidney (whole kidney, isolated glomeruli, and renal tubules) and glomerular ultrastructure were evaluated. Diabetes was associated with a significant increase in collagen-related fluorescence in the aorta and kidney. Aminoguanidine prevented the increases in collagen-related fluorescence in aorta, isolated glomeruli, and renal tubules but not in whole kidney. Diabetes was associated with increased albuminuria, fractional mesangial volume, and glomerular basement membrane (GBM) thickness. Aminoguanidine attenuated the rise in albuminuria and prevented mesangial expansion without influencing GBM thickness in diabetic rats. The concomitant changes in collagen-related fluorescence, albuminuria, and mesangial expansion with aminoguanidine therapy are consistent with the hypothesis that AGEs may play a role in the development of diabetic nephropathy.
Development of Muscle Insulin Resistance After Liver Insulin Resistance in High-Fat–Fed Rats
Authors: Kraegen Edward W , Clark Peter W , Jenkins Arthur B , Daley Eugene A , Chisholm Donald J , Storlien Leonard H
Published: September 2013

Muscle and hepatic insulin resistance are two major defects of non-insulin-dependent diabetes mellitus. Dietary factors may be important in the etiology of insulin resistance. We studied progressive changes in the development of high-fat–diet–induced insulin resistance in tissues of the adult male Wistar rat. In vivo insulin action was compared 3 days and 3 wk after isocaloric synthetic high-fat or high-starch feeding (59 and 10% cal as fat, respectively). Basal and insulin-stimulated glucose metabolism were assessed in the conscious 5- to 7-h fasted state with the euglycemic clamp (600 pM insulin) with a [3-3H]-glucose infusion. Fat feeding significantly reduced suppressibility of hepatic glucose output by insulin after both 3 days and 3 wk of diet (P < 0.01). However, a significant impairment of insulin-mediated peripheral glucose disposal was only present after 3 wk of diet. Further in vivo [3H]-2-deoxyglucose uptake studies supported this finding and demonstrated adipose but not muscle insulin resistance after 3 days of high-fat feeding. Muscle triglyceride accumulation due to fat feeding was not significant at 3 days but had doubled by 3 wk in red muscle (P < 0.001) compared with starch-fed controls. By 3 wk, high-fat—fed animals had developed significant glucose intolerance. We concludethat fat feeding induces insulin resistance in liver and adipose tissue before skeletal muscle with early metabolic changes favoring an oversupply of energy substrate to skeletal muscle relative to metabolic needs. This may generate later muscle insulin resistance.
Deterioration of Islet β-Cell Function After Hemipancreatectomy in Dogs
Authors: Stagner John I , Samols Ellis
Published: September 2013

The metabolic consequences of hemipancreatectomy in living pancreas donors were tested in a dog model in which a 50% lobe-specific pancreatectomy was performed. Removal of the dorsal lobe (analogous to a donor, n = 4) resulted in a progressive increase in fasting glucose during 12 mo from 5.32 ± 0.16 to 8.17 ± 0.28 mM and a decrease in fasting insulin from 54 ± 3 to 6.0 ± 2.4pM and glucose clearance (Kg) from 3.00 ± 0.22 to 1.00 ± 0.06 mM. Removal of the ventral lobe (analogous to a recipient, n = 5)did not result in a change in fasting glucose or Kg during 12 mo, although fasting insulin was reduced from 36.0 ± 1.8 to 18.00 ± 1.93 pM. In vitro perfusion of the remnants after 1 yr showed a deterioration in glucose-stimulated insulin secretion (5–11 mM) by the dorsal remnant (18 ± 11 vs., 232 ± 37%) and the ventral remnant (2.6 ± 19 vs. 87 ± 13%). The dorsal remnant had a higher response than the ventral remnant (46 ± 23 vs. −16 ± 10%, respectively) to severe hyperglucosuria (11–27.7 mM). Insulin content was unchanged in the dorsal remnant (224 ± 16 vs. 180 ± 14μg/g), but was reduced in the ventral remnant (65 ± 14 vs. 154 ± 15μg/g). Invitro insulin pulse intervals were reduced in both remnants (5.3 ± 0.2 min vs. control 7.00 ± 0.18 min). Because of the above effects on the donor when the dorsallobe is removed, the continued use of hemipancreatectomy as a source of transplantable tissue must be questioned.
Age-Dependent Expression of Protein Kinase C Isoforms in Rat Islets
Authors: Fletcher Donald J , Ways D Kirk
Published: September 2013

The appearance of the biphasic insulin secretory response several days after birth suggests that maturation of a critical step in stimulus-secretion coupling occurs during the early neonatal period. To clarify the role of protein kinase C (PKC) during this time, we examined the pancreatic islets of adult, 3-day neonatal, and 19-day fetal rats for the presence of different PKC isoenzymes. Western-blot analysis of islet extracts showedthe presence of PKC isoforms in both adult and neonatal tissues. Immunocytochemistry of adult islets revealed a differential expression in islet cell types. PKC-α was found only in β-cells, PKC-γ in α-cells, and PKC-ε in δ-cells and vascular walls. Immunoreactivity for PKC-β was not detected in any cell type. All three isoenzymes were also present in neonatal islets; however, in contrast to adult tissue, immunoreactivity for either PKC-α or PKC-γ was present inrelatively few cells. There was no apparent immunoreactivity for PKC-α or PKC-γ in fetal islets, although these tissues contained strong staining for insulin and glucagon. These data show that three of the PKC isoforms are restricted to a particular islet cell type, where they may play a unique role in the secretion of a specific hormone. Moreover, our results demonstrate that these enzymes, especially PKC-γ, appearduring the early neonatal period. This age-dependent expression may be linked to the development of the biphasic insulin release response.
Nutrition and Somatomedin: XXVI. Molecular Regulation of IGF-I by Insulin in Cultured Rat Hepatocytes
Authors: Phillips Lawrence S , Goldstein S , Pao C -I
Published: September 2013

Although decreased levels of circulating insulinlike growth factor I (IGF-I) and hepatic IGF-I mRNA in diabetic animal models support a role for insulin in IGF-I regulation, it has been difficult to study the effects of insulin in vitro. Few immortal cell lines exhibit hormone-responsive production of IGF-I, and studies of cultured hepatocytes have often been inconclusive because conventional methods may not reproduce the IGF-I transcripts recognized in vivo. We have modified the hepatocyte isolation and RNA extraction procedures to circumvent this problem, resulting in transcripts of 1, 2, and 7.5 kb. With increasing insulin from 10−10 to 10−6 M, dexamethasone from 10−10 to 10−7 M, and amino acids from 1 to 10 × rat arterial levels, IGF-I release rose by 226, 257, and 447%, respectively (P < 0.05), with correlated changes in IGF-I mRNA (r = 0.75, P < 0.005). In the presence of 5 × amino acids and 10−7 M dexamethasone, insulin-stimulated IGF-I release was dose dependent, increasing 183% at 10−6 M (P < 0.01). Across a broad range of amino acid concentrations (0.25–6.25 ×), insulin provided consistent stimulation of both IGF-I mRNA content and release of IGF-I. Cells cultured for 2 days at 10−10 M insulin and then 2 days at 10−6 M insulin released 66% more IGF-I than cells cultured 4 days at 10−10 M insulin (P < 0.01). Hepatocyte IGF-I release was correlated strongly with content of IGF-I mRNA, both sum of transcripts (r = 0.76, P < 0.001) and individual transcripts. Insulin appears to regulate IGF-I release at the mRNA level in hepatocyte primary culture. This system should be a useful tool for further studies of molecular mechanisms of IGF-I regulation.
Glyburide-Stimulated Glucose Transport in Cultured Muscle Cells via Protein Kinase C–Mediated Pathway Requiring New Protein Synthesis
Authors: Davidson Mayer B , Molnar I Gabriella , Furman Anchel , Yamaguchi Dean
Published: September 2013

To study the mechanism of action of sulfonylurea agents on peripheral tissues without the potentially confounding influences of insulin, the direct effect of glyburide (i.e., in the absence of insulin) was evaluated in the L6 cultured myogenic cell line. Glyburide approximately doubled the incorporation of [14C]-glucose into glycogen. The rate-determining enzymes of glycogen metabolism, glycogen synthase and glycogen phosphorylase, were unaffected by the drug. Glucose transport (2-deoxyglucose uptake) was also ∼ doubled. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) also doubled glucose transport and showed the same lag period (4–6 h) as glyburide before an effect occurred. Blockade of protein kinase C activity by either 1-(5-isoquinolinesulfonyl)-2 methyl piperazine (H7) or chronic exposure to TPA completely abolished the stimulation by glyburide. Cycloheximide, a protein synthesis inhibitor, also completely eliminated the effect of glyburide. The presence of ATP-sensitive K+ channels was assessed by measuring 86Rb efflux in ATP-depleted L6 muscle cells and RINm5F cells (which served as a positive control). Such channels were present and responded appropriately to glyburide and diazoxide in pancreatic β-cells but were not present in muscle cells. Glyburide stimulation of glucose transport was completely eliminated by both Quin 2, an intracellular chelator of Ca2+, and verapamil, a Ca2+ channel blocker. However, glyburide did not raise intracellular Ca2+ levels. We conclude that glyburide stimulates glucose transport in cultured L6 muscle cells by a protein kinase C–mediated pathway that requires new protein synthesis. Although intracellular Ca2+ metabolism may also be involved, the initial step in the mechanism of action is probably different between pancreatic β-cells and muscle cells.
The Pancreatic Islet as Rubik's Cube: Is Phospholipid Hydrolysis a piece of the Puzzle?
Authors: Metz Stewart A
Published: September 2013

At least three types of phospholipase exist in the β-cells of the pancreatic islet. Data regarding their physiological activation are incomplete but suggest that glucose (or its metabolite glyceraldehyde) either activates or potentiates the activation of several phospholipases. At least seven phospholipid hydrolysis by-products (diacylglycerol, myo-inositol 1,4,5-trisphosphate, lysophospholipids, arachidonic acid and its cyclooxygenase- and lipoxygenase-derived metabolites, phosphatidate) have been demonstrated to have effects compatible with their postulated roles as mediators or modulators of islet function. Presumptive mechanisms of action have been tentatively identified for these metabolites. However, key studies in the puzzle are missing, and current methodologies have important limitations. Shortcomings include the paucity of measurements of the mass of metabolites; the frequent use of static incubations rather than perfusions; a lack of complete time- and agonist concentration–dependence curves; the equation of metabolite accumulation with rates of metabolite generation (which ignores metabolite removal as a key variable); the use of nonspecific, insensitive, or ambiguous phospholipase assays; and the need for more studies directly correlating lipid metabolism and insulin secretion in physiologically functioning preparations. Like Rubik's Cube, the pancreatic islet is a dynamic puzzle comprised of many interrelated components requiring proper alignment and integration. Phospholipid turnover is one “panel” in the islet; however, an obligate role for phospholipase activation in glucose-induced insulin secretion is not yet rigorously established, despite tantalizing, inferential evidence. It may be that glucose serves principally to potentiate the phospholipase and secretory responses to other signals that act by initiating phospholipid hydrolysis.
Direct Involvement of Macrophages in Destruction of β-Cells Leading to Development of Diabetes in Virus-Infected Mice
Authors: Baek Hong-Sun , Yoon Ji-Won
Published: September 2013

A single administration of complete Freund's adjuvant (CFA), type 1 carrageenan (Car), or silica 7, 2, and 2 days, respectively, before infection with a low dose (1 × 102 plaque-forming units/mouse) of encephalomyocarditis D (EMC-D) virus resulted in a significant increase in the incidence of diabetes in SJL/J mice (100%) compared with untreated EMC-D virus–infected mice (40%). Peritoneal macrophages were isolated from uninfected SJL/J mice, which had been treated once with silica, and transferred into SJL/J mice 2 days before low-dose EMC-D infection. Approximately 90% of the mice became diabetic, whereas 30% of mice that received virus alone became diabetic. The depletion of macrophages by treatment with the combined anti-Mac-1 and anti-Mac-2 monoclonal antibodies after a single administration of CFA, Car, or silica resulted in almost complete prevention of β-cell destruction in EMC-D virus–infected mice. Furthermore, none of the mice in which macrophages were depleted by long-term treatment with silica and 10% of the mice treated with Car before virus infection became diabetic. On the basis of these observations, we conclude that macrophages are directly involved in the destruction of β-cells, leading to the development of clinical diabetes in EMC-D virus–infected mice.
Aggregation of Subclinical Autonomic Nervous System Dysfunction and Autoantibodies in Families With Type I Diabetes
Authors: Brown Florence M , Watts Mike , Rabinowe Steven L
Published: September 2013

The purpose of our study was to evaluate the occurrence of autonomic nervous system autoantibodies (ANS) in the nondiabetic family members of insulin-dependent (type I) diabetic subjects. We studied 24 families, including 45 nondiabetic parents and 53 nondiabetic siblings of a type I diabetic proband. One hundred one nondiabetic population control subjects were also studied. Stored sera from nondiabetic family members and control subjects were evaluated for the presence of complement-fixing (CF) adrenal medullary antibodies (CF-ADM), sympathetic ganglia antibodies (CF-SG), and vagus nerve antibodies (CF-V) by indirect immunofluorescence. HLA-DR3 and -DR4 typing was performed on 42 nondiabetic family members and 104 diabetic subjects. One or more CF-ANS were in 45 of 93 (40%) nondiabetic family members compared to 2 of 70 (2.8%) control subjects. CF-SG were in 28 of 92 (30%) family members compared to 0 of 101 control subjects (P = 0.0001). CF-V were in 25 of 95 (26%) family members compared to 0 of 76 control subjects (P = 0.0001). CF-ADM were in 10 of 83 (12%) family members compared to 2 of 70 (2.8%) control subjects (P = 0.056). There was no HLA-DR3 or HLA-DR4 association with ANS. Subclinical autonomic dysfunction was demonstrated in 3 of 4 family members with autoantibodies compared to 0 of 4 family members without autoantibodies.
Decrease of Stimulated Amylin Release Precedes Impairment of Insulin Secretion in Type II Diabetes
Authors: Ludvik Bernhard , Lell Bert , Hartter Engelbert , Schnack Christoph , Prager Rudolf
Published: September 2013

Amylin, a 37–amino acid polypeptide, has been identified as the major protein component of pancreatic amyloid deposits in patients with non-insulin-dependent (type II) diabetes mellitus. Amylin is stored and released together with insulin and has been proposed to play a major role in the pathogenesis of type II diabetes. To compare amylin release and its proportion to insulin secretion under different metabolic conditions, oral and intravenous glucose tolerance tests (OGTT and IVGTT, respectively) were performed in healthy, lean control subjects, obese patients with normal and impaired glucose tolerance (NGT and IGT, respectively), and obese type II diabetic patients. Compared with control subjects, basal and stimulated amylin secretion during OGTT was significantly higher in obese patients with NGT and IGT but not in type II diabetic patients. The integrated amylin response was significantly higher in obese patients with NGT than lean control subjects and type II diabetic patients matched for degree of obesity. The amylin-insulin ratio decreased slightly in obese subjects with NGT and IGT and significantly in type II diabetic patients. Amylin secretion was significantly stimulated during IVGTT in control subjects and obese patients with NGT and IGT but not in type II diabetic patients. These findings suggest that amylin is physiologically released by pancreatic β-cells in a constant ratio to insulin in nondiabetic subjects. Glucose-stimulated amylin secretion is increased in obese subjects with NGT and IGT. In type II diabetes mellitus, amylin secretion relative to that of insulin is decreased, and amylin is not stimulated by IVGTT.
Insulinlike Effects of Sodium Selenate in Streptozocin-Induced Diabetic Rats
Authors: McNeill John H , Delgatty Heather L M , Battell Mary L
Published: September 2013

Treatment of streptozocin (STZ)-induced diabetic rats with sodium selenate (10–15 μmol · kg−1 · day−1) for 7 wk resulted in a decrease in plasma glucose, food intake, and water intake to control or near control levels. Plasma insulin was reduced in control rats given sodium selenate to the level found in the diabetic and treated diabetic group. Treatment did not affect control rats with regard to the other measurements cited. Sodium selenate enhanced weight gain in responding diabetic rats to that seen in controls; sodium selenate's actions thus resembled those of insulin. Thus selenate, like vanadium, appears to have insulinlike effects when administered in vivo.
Risk Factors for Development of Diabetic Nephropathy and Retinopathy in Jewish IDDM Patients
Authors: Kalter-Leibovici Ofra , Van Dyk David J , Leibovici Leonard , Loya Nissim , Erman Arie , Kremer Israel , Boner Geoffrey , Rosenfeld Joseph B , Karp Moshe , Laron Zvi
Published: September 2013

Risk factors associated with diabetic microvascular complications, with special reference to ethnic origin, were looked for in 231 young Jewish insulin-dependent diabetes mellitus (IDDM) patients with duration of diabetes ≥10 yr. Median age at diagnosis of diabetes was 9.2 yr (range 0.04–26.2 yr), and median duration of the disease was 15.3 yr (range 10.0–37.2 yr). Sixty-three percent of the patients were Ashkenazi Jews, and 37% were non-Ashkenazi Jews. HbA1 was evaluated every 3 mo in the last 10 yr of follow-up, and albumin excretion rate was tested in three 24-h urine collections. Direct and indirect ophthalmoscopy was performed every year since diagnosis of diabetes, and if retinal pathology was suspected, color photographs were taken. Microalbuminuria was detected in 31% and macroalbuminuria in 7% of the patients. Nonproliferative and proliferative retinopathy was found in 44 and 12% of the patients, respectively. On logistic regression analysis, two variables were significantly and independently associated with diabetic nephropathy—non-Ashkenazi origin and mean HbA1 values over the first 5 of 10 yr of follow-up. Variables significantly and independently related to diabetic retinopathy were non-Ashkenazi origin, mean HbA1 values over the last 10 yr of follow-up, and duration of diabetes. Because non-Ashkenazi Jews in Israel are of lower socioeconomic status than Ashkenazi Jews, we stratified our patients according to their socioeconomic parameters, median HbA1 values, and duration of diabetes. Non-Ashkenazi patients were at a higher risk to develop complications in all strata. We further stratified patients into four quartiles according to mean HbA1 values; there was a steep increase in the risk to develop macroalbuminuria in the 4th quartile of HbA1 (odds ratio [OR] 4.3 vs. 1.2 in the 3rd quartile) and proliferative retinopathy (OR 13.0 in the 4th quartile of HbA, vs. 2.8 in the 3rd quartile). We conclude that non-Ashkenazi Jewish IDDM patients are at significant risk to develop microvascular complications, independent of their glycemic control, duration of diabetes, and socioeconomic status. Careful follow-up and special efforts toward improving glycemic control should be focused on high-risk subgroups of patients.
Reduced Neuroendocrine and Symptomatic Responses to Subsequent Hypoglycemia After 1 Episode of Hypoglycemia in Nondiabetic Humans
Authors: Heller Simon R , Cryer Philip E
Published: September 2013

To test the hypothesis that hypoglycemia itself causes reduced neuroendocrine and symptomatic responses to subsequent hypoglycemia, we measured those responses during clamped hypoglycemia (2.8 mM) on consecutive mornings on two occasions, with interval afternoon (1400–1600) hypoglycemia (3 mM) on one occasion and interval afternoon euglycemia (5 mM) on the other, in nine nondiabetic humans. None of the measured responses were reduced by interval euglycemia. In contrast, plasma epinephrine (P < 0.005), glucagon (P < 0.005), pancreatic polypeptide (P < 0.01), cortisol (P < 0.02), and total (P < 0.001), neurogenic (P < 0.001) and neuroglycopenic (P < 0.05) symptom responses to morning hypoglycemia were reduced after interval afternoon hypoglycemia. Thus, a single episode of hypoglycemia caused a generalized reduction of the neuroendocrine and symptomatic responses to subsequent hypoglycemia, a finding that may be important to the pathogenesis of iatrogenic hypoglycemia in insulin-dependent diabetes mellitus.
Restoration of Na+-K+ Pump Activity and Resting Membrane Potential by myo-Inositol Supplementation in Neuroblastoma Cells Chronically Exposed to Glucose or Galactose
Authors: Yorek Mark A , Dunlap Joyce A , Stefani Mark R
Published: September 2013

myo-Inositol uptake by culture neuroblastoma cells at a concentration of myo-inositol <50 μM was largely Na+ dependent. Exposing neuroblastoma cells to media supplemented with increasing concentrations of myo-inositol resulted in an increase in myo-inositol accumulation and intracellular content, but myo-inositol incorporation into phospholipids was not increased. The data indicate that myo-inositol exists as separate pools in neuroblastoma cells, and one or more of these pools may contribute to phospholipid synthesis. Exposing neuroblastoma cells to an increased concentration of glucose caused a decrease in myo-inositol uptake by two separate mechanisms. Acute exposure of the cells to 30 mM glucose caused a myo-inositol concentration–dependent decrease in Na+-dependent myo-inositol uptake. We propose that the acute inhibition of myo-inositol uptake by glucose is likely due to a competitive type of inhibition. Chronic exposure of cells to media containing 30 mM glucose or 30 mM galactose also caused decreases in myo-inositol uptake and incorporation into inositol phospholipids and intracellular myo-inositol content. This decrease in myo-inositol metabolism persisted at a higher concentration of external myo-inositol than the acute inhibition. Supplementing media containing 30 mM glucose or 30 mM galactose with 250 μM myo-inositol restored myo-inositol metabolism and content. The inhibition of myo-inositol uptake by cells chronically exposed to increased concentrations of glucose or galactose was due to a noncompetitive type of inhibition that was blocked by the addition of sorbinil. Chronic exposure of neuroblastoma cells to media containing 30 mM glucose or 30 mM galactose caused a decrease in Na+-K+-ATPase transport activity and resting membrane potential. Both of these abnormalities were corrected by supplementing the media with 250 μM myo-inositol. myo-lnositol depletion in neuroblastoma cells exposed to increased concentrations of glucose may occur by two different mechanisms and may be responsible for alterations in Na+-K+-ATPase transport activity and resting membrane potential.
Role of Glucose, Insulin, and Glucagon in Glycogen Mobilization in Human Hepatocytes
Authors: López M Pilar , Gómez-Lechón M José , Castell José V
Published: September 2013

This study investigated the role of glucose, insulin, and glucagon in the activation of glycogen catabolism in cultured human hepatocytes. Basal glycogenolysis in unstimulated human hepatocytes was low (only 19% of initial glycogen content was degraded in a 4-h incubation) and insensitive to changes in external glucose concentration (from 10 to 0 mM). Both glycogenolysis and glucose output could be significantly stimulated by 35 ng/L glucagon or 105 pM dibutyryl cAMP; half-maximal effect was found with 28 × 102 ng/L glucagon and 4 × 105 pM dibutyryl cAMP. After a 3-h exposure to 35 × 103 ng/L glucagon, >90% of glycogen content of human hepatocytes was mobilized. This caused a 4.6-fold increase in the rate of glucose output to the medium compared with nonstimulated cells. About 85% of degraded glycogen rendered glucose to the medium. Insulin (104 pM) was able to totally suppress basal glycogenolysis; insulin was also essential to reverse the action of glucagon in hepatocytes incubated with glucagon, whereas glucose alone, even at postprandial concentration, was unable to reverse glucagon action. In summary, these experiments show that the mobilization of glycogen stores of human hepatocytes, as it occurs during the postabsorptive periods in humans, is largely dependent on the presence of glucagon and is not simply due to a decrease of external glucose. Insulin, on the other hand, was essential to suppress both basal and glucagon-activated glycogenolysis.
Influence of Dietary Fat Composition on Development of Insulin Resistance in Rats: Relationship to Muscle Triglyceride and ω-3 Fatty Acids in Muscle Phospholipid
Authors: Storlien Leonard H , Jenkins Arthur B , Chisholm Donald J , Pascoe Wendy S , Khouri Sue , Kraegen Edward W
Published: September 2013

High levels of some but not all dietary fats lead to insulin resistance in rats. The aim of this study was to investigate the important determinants underlying this observation. Insulin action was assessed with the euglycemic clamp. Diets high in saturated, monounsaturated (ω-9), or polyunsaturated (ω-6) fatty acids led to severe insulin resistance; glucose infusion rates [GIR] to maintain euglycemia at ∼1000 pM insulin were 6.2 ± 0.9, 8.9 ± 0.9, and 9.7 ± 0.4 mg · kg−1 · min−1, respectively, versus 16.1 ± 1.0 mg · kg−1 · min−1 in chow-fed controls. Substituting 11% of fatty acids in the polyunsaturated fat diet with long-chain ω-3 fatty acids from fish oils normalized insulin action (GIR 15.0 ± 1.3 mg · kg−1 · min−1). Similar replacement with short-chain ω-3 (α-linolenic acid, 18:3ω3) was ineffective in the polyunsaturated diet (GIR 9.9 ± 0.5 mg · kg−1 · min−1) but completely prevented the insulin resistance induced by a saturated-fat diet (GIR 16.0 ± 1.5 mg · kg−1 · min−1) and did so in both the liver and peripheral tissues. Insulin sensitivity in skeletal muscle was inversely correlated with mean muscle triglyceride accumulation (r = 0.95 and 0.86 for soleus and red quadriceps, respectively; both P = 0.01). Furthermore, percentage of long-chain ω-3 fatty acid in phospholipid measured in red quadriceps correlated highly with insulin action in that muscle (r = 0.97). We conclude that 1) the particular fatty acids and the lipid environment in which they are presented in high-fat diets determine insulin sensitivity in rats; 2) impaired insulin action in skeletal muscle relates to triglyceride accumulation, suggesting intracellular glucose–fatty acid cycle involvement; and 3) long-chain ω-3 fatty acids in phospholipid of skeletal muscle may be important for efficient insulin action.
Intermolecular Phosphorylation of Insulin Receptor as Possible Mechanism for Amplification of Binding Signal
Authors: Hayes Gary R , Lydon Lance D , Lockwood Dean H
Published: September 2013

Clustering of cell-surface insulin receptors has led to the speculation that intermolecular phosphorylation of unoccupied receptors catalyzed by ligand-occupied receptors within the cluster could be a mechanism by which the insulin-binding signal is amplified. We examined whether insulin receptors can be phosphorylated by an intermolecular mechanism. In this study, we used highly purified insulin receptors isolated from rat liver plasma membranes and human placental membranes. Rat liver insulin receptors were “activated” by incubation with 10 nM insulin in the presence of ATP. Subsequent to removal of insulin by immunodepletion, these receptors were used as an enzyme source to study phosphorylation of unphosphorylated “substrate” human receptors. Initially, we found no evidence that the addition of activated rat receptors increased phosphorylation of human receptors, when assessed by immunoprecipitation with a human-specific monoclonal antibody. To examine the possibility that these negative results were due to insufficient receptor concentration, activated human receptors were mixed with unphosphorylated substrate receptors at concentrations up to 60 μg/ml. In this study, we found that addition of activated receptors resulted in increased phosphorylation of the substrate receptors at the highest concentrations employed. These are the first data indicating that insulin receptors per se are capable of intermolecular phosphorylation. In vivo, this could be the initial step in amplifying the insulin-binding signal.
Metabolic Alterations in Adulthood After Intrauterine Development in Mothers With Mild Diabetes
Authors: Assche Frans Andre Van , Aerts Leona , Holemans Kathleen
Published: September 2013

We studied the long-term effects of maternal diabetes mellitus on the offspring of experimentally induced diabetic Wistar rats. When stressed by an intravenous glucose load, the adult female offspring had impaired glucose tolerance and developed gestational diabetes mellitus when pregnant. Our results show that even mild diabetes mellitus induces an abnormal intrauterine milieu that causes morphological and functional changes in fetal development with consequences for later life.