bluuebunny/crossref_metadata_2025 huggingface dataset:
Intraportal Transplantation of Pancreatic Islets Into Livers of Diabetic Rats: Reinnervation of Islets and Regulation of Insulin Secretion by the Hepatic Sympathetic Nerves
Authors: Gardemann Andreas , Jungermann Kurt , Groβe Volker , Cossel Lothar , Wohlrab Frank , Halm Hans Jürgen , Blech Wolfgang , Hildebrandt Wolfgang
Published: September 2013

Two weeks after intraportal transplantation of 2,000 neonatal pancreatic islets, recipient rats completely recovered from streptozotocin-induced diabetes. The reversal of diabetes could be documented by the normalization of blood glucose levels, by a restored weight gain, by normal glucagon and insulin levels in blood, and by a disappearance of polyuria and polydipsia. The reversal remained stable for at least 9 months. This study determined whether intraportally transplanted pancreatic islets were reinnervated after transplantation and whether the secretion of insulin and glucagon from pancreatic islets might be modulated by the vegetative innervation of recipient livers. Predominantly catecholaminergic but also cholinergic nerve fibers were detected not only within the portal tracts around hepatic arteries, portal veins, and bile ducts, but also at the borderline of hepatocytes and β-cells and in islet cell complexes between β-cells. Corresponding electron micrographs showed β-cells in close contact with axons of nonmyelinated nerve fibers. Isolated livers were single pass perfused via both the hepatic artery and the portal vein. An increase in glucose level from 5 to 14 mmoW enhanced hepatic glucose uptake and increased insulin secretion from transplanted islets with a biphasic secretion profile but had no effect on glucagon output. Stimulation of the nerve plexus around the hepatic artery and the portal vein (7.5 Hz, 2 min), which activates primarily the sympathetic system, not only reduced glucose uptake and perfusion flow but also completely reversed the glucose-stimulated increase in insulin secretion. Nerve stimulation did not influence glucagon secretion. The α1-aradrenergic antagonist prazosin and the β-blocker propranolol completely blocked the nerve stimulation-dependent alterations in glucose balance and in perfusion flow but did not affect the reversal of the glucose-stimulated increase in insulin release caused by nerve stimulation. This indicates indirectly that the inhibition by sympathetic liver nerves of insulin secretion was mediated via α2-receptors as in normal pancreatic islets. Experiments with the α2-adrenergic antagonist yohimbine were in line with this conclusion.
Repeatability of Insulin Sensitivity and Glucose Effectiveness From the Minimal Model: Implications for Study Design
Authors: Steil Garry M , Murray Joseph , Bergman Richard N , Buchanan Thomas A
Published: September 2013

To determine the repeatability of insulin sensitivity measurements generated by the minimal model, we subjected 11 normal men to 3 frequently sampled intravenous glucose tolerance tests (FSIGTs) over the course of 12 days under conditions of fixed diet and limited physical activity. FSIGTs were analyzed by the minimal model using a full, 30-sample data set, as well as a reduced, 12-sample data set that has been proposed for population studies. Minimal model insulin sensitivity index (Si) calculated from the 30-sample data set averaged 0.8 ± 0.083 × 10−4 min−1 · (pmol/1)−1 (range 0.10–1.64 × 10−4 min−1 · (pmol/I)−1 with an average interday coefficient of variation (CV) of 20.2 ± 3.2% (range 6–44%). Glucose effectiveness (SG) was slightly less repeatable, with an average interday variability of 25.1 ± 8.8%. The mean CVs for first-phase insulin secretion (20.1 ± 3.5%) and total insulin secretion (21.4 ± 3.2%) were similar to the CV for Sp Mean insulin sensitivity calculated from the 12-sample data set (0.82 ± 0.08 × 10−4 min−1 · (pmol/1)−1 was not significantly different from the mean calculated from the full data set (P = 0.37, paired Student's t test). However, the mean CV of Sx calculated from the reduced data set tended to be greater than that calculated from the full data set (27.7 ± 5.4% vs. 20.2 ± 3.2%). Power calculations using the observed variances from the full and reduced data sets indicated that the full sample protocol is preferable for small studies designed to detect small changes in Si, whereas the reduced sample protocol is appropriate for studies with large numbers of subjects or large anticipated changes in Si
Individual Differences in Neurobehavioral Disruption During Mild and Moderate Hypoglycemia in Adults With IDDM
Authors: Gonder-Frederick Linda A , Cox Daniel J , Driesen Naomi R , Ryan Christopher M , Clarke William L
Published: September 2013

This study investigated the neurobehavioral effects of mild and moderate hypoglycemia in adults with insulin-dependent diabetes mellitus (IDDM). On 2 consecutive days, 26 subjects were tested in a counterbalanced, randomized, single-blind, crossover design. On the experimental day, subjects performed tests at 6.4, 3.6, and 2.6 mmol/l and again after glycemic recovery to 6.3 mmol/l. On the control day, subjects performed tests four times at euglycemia. Three months after testing, 15 subjects repeated the experimental day protocol. Results demonstrated that both mild and moderate hypoglycemia significantly disrupted performance. However, performance deterioration varied substantially across individual subjects. Men exhibited significantly more deterioration than women at mild hypoglycemia, and subjects with a history of unconsciousness due to hypoglycemia exhibited more deterioration than subjects with no such history. Individual deterioration scores during repeat testing significantly correlated with performance during original testing. Recovery from hypoglycemia-related impairment varied across individuals and was correlated with degree of impairment during hypoglycemia. These results suggest that the glycemic threshold for onset and recovery from neurobehavioral deterioration with hypoglycemia, as well as degree of impairment experienced, varies across individuals. Furthermore, these individual differences are stable across time.
Glucose Metabolism During the Starved-To-Fed Transition in Obese Patients With NIDDM
Authors: Féry Françhise , Balasse Edmond O
Published: September 2013

To analyze the effects of short-term fasting on postprandial glucose metabolism in non-insulin-dependent diabetes mellitus (NIDDM), two groups of nine obese NIDDM patients and two comparable groups of control subjects underwent a 5-h oral glucose tolerance test after either 14 h or 4 days of fasting. The fluxes and the rates of oxidation and storage of glucose were measured using a dual isotope technique combined with indirect calorimetry. The effect of fasting on insulin action and beta-cell responsiveness was tested in an additional group of six obese NIDDM patients with a euglycemic hyperinsulinemic clamp followed by an intravenous glucagon test. In the diabetic patients, fasting enhanced beta-cell response to glucose and glucagon and did not modify insulin action. This response differs from that of nondiabetic subjects in whom fasting is known to impair insulin secretion and action. Regarding glucose fluxes, it was observed that in the overnight-fasted state, the incremental tissular disposal following glucose ingestion was reduced by ∼ 50% in the diabetic versus control subjects in relation to an ∼ 62% impairment in glucose storage. After fasting, incremental tissular disposal was restored to normal, glucose oxidation was virtually abolished, and storage was increased ∼ threefold. Thus, in NIDDM patients, fasting corrects the defect in glycogen storage without modifying the action of insulin on glucose uptake and improves beta-cell responsiveness, the latter two effects being opposite to those observed in nondiabetic subjects.
Proinsulin and Specific Insulin Concentration in High- and Low-Risk Populations for NIDDM
Authors: Haffner Steven M , Bowsher Ronald R , Mykkänen Leena , Hazuda Helen P , Mitchell Braxton D , Valdez Rodolfo A , Gingerich Ronald , Monterossa Ana , Stern Michael P
Published: September 2013

Hyperinsulinemia and insulin resistance have been implicated as risk factors for the development of non-insulin-dependent diabetes mellitus (NIDDM). Recent data suggest that proinsulin may comprise a large proportion of immunoreactive insulin in subjects with NIDDM and possibly in those with impaired glucose tolerance (IGT) as well. Increased proinsulin concentrations are thought to be an early indicator of a failing pancreas. We examined proinsulin, insulin (using an assay that does not display appreciable cross-reactivity with proinsulin), and the fasting proinsulin:insulin ratio in 206 nondiabetic Mexican-American (a high-risk population for NIDDM) and 123 nondiabetic non-Hispanic white (a low-risk population for NIDDM) participants in the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease. Mexican-Americans had significantly higher fasting and 2-h proinsulin and insulin levels but similar fasting proinsulin:insulin ratios compared with non-Hispanic whites. After statistical adjustment for age, body mass index, waist-to-hip ratio, and glucose tolerance status, Mexican-Americans continued to have higher fasting and 2-h insulin and fasting and 2-h proinsulin concentrations but similar proinsulin:insulin ratios compared with non-Hispanic whites. The fasting proinsulin:insulin ratio was higher in 85 subjects with NIDDM compared with subjects with IGT or normal glucose tolerance (0.31, 0.09, and 0.07, respectively). Thus, nondiabetic subjects from a high-risk population for NIDDM are hyperinsulinemic (using an assay that does not cross-react with proinsulin) and, further, do not secrete more proinsulin relative to insulin itself than do nondiabetic subjects from a low-risk population.
Muscle Sympathetic Nerve Activity in Response to Glucose Ingestion: Impact of Plasma Insulin and Body Fat
Authors: Spraul Maximilian , Anderson Erling A , Bogardus Clifton , Ravussin Eric
Published: September 2013

Carbohydrate intake stimulates sympathetic nervous system activity in lean subjects, whereas in obese subjects, the results have been inconsistent. The aim of this study was to directly measure sympathetic neural outflow to skeletal muscle in response to a 75-g oral glucose tolerance test (OGTT) in 15 Pima Indian and 16 Caucasian men, matched for body fat and age, but covering a large range of body weight (57–113 kg) and body fat (4–41%). Fasting muscle sympathetic nerve activity (MSNA) correlated positively with body fat (r = 0.73; P = 0.001) in Caucasians but not in Pima Indians, whereas the increase in MSNA during the OGTT correlated negatively with the percentage of body fat (r = −0.38, P = 0.03) independently of race. In each subject, the increase in MSNA over time correlated positively with the increase in plasma insulin levels, but the slopes of these relationships were inversely related to the percentage of body fat (r = −0.52, P = 0.003) independently of race. In conclusion, obesity is associated with a higher fasting sympathetic neural outflow to muscle but a blunted increase in response to an oral glucose load despite a larger increase in plasma insulin levels. This blunted response may represent another feature of the obesity/insulin resistance syndrome.
Pioglitazone Increases Insulin Sensitivity, Reduces Blood Glucose, Insulin, and Lipid Levels, and Lowers Blood Pressure, in Obese, Insulin-Resistant Rhesus Monkeys
Authors: Kemnitz Joseph W , Elson Diane F , Roecker Ellen B , Baum Scott T , Bergman Richard N , Meglasson Martin D
Published: September 2013

The antidiabetic effects of pioglitazone hydrochloride were evaluated in 6 spontaneously obese, insulin-resistant rhesus monkeys. The animals were studied during six successive 2-wk treatment phases separated by 2-wk rest periods: two placebo phases; 0.3, 1.0, and 3.0 mg · kg−1 · day−1 pioglitazone hydrochloride phases; and a final placebo phase. During the second week of each treatment phase, serum insulin (immunoreactive insulin [IRI]), plasma glucose, and serum triglyceride (TG) levels were measured after an overnight fast and after a standardized meal. Blood pressure was measured and glucose tolerance tests (modified minimal model protocol) were performed a few days after the meal tests. Pioglitazone hydrochloride significantly improved fasting and postprandial levels of IRI, plasma glucose, and TG in a dose-related manner (P < 0.05). Fasting values during treatment with 3.0 mg · kg−1 · day−1 were reduced by 64% for IRI, 19% for plasma glucose, and 44% for TG compared with the placebo phase before treatment. Efficacy of pioglitazone hydrochloride was more marked for those animals with fasting hyperglycemia. Insulin sensitivity was increased by pioglitazone hydrochloride (P = 0.05), whereas glucose effectiveness and glucose disappearance rate were not detectably affected. Systolic and mean arterial blood pressures were significantly decreased by pioglitazone hydrochloride (P < 0.05). No toxic side effects of pioglitazone hydrochloride treatment were noted.
Skeletal Muscle Vascular Transport Capacity in Diabetic Rats
Authors: Sexton William L
Published: September 2013

This study aimed to determine the effect of long-term (17–20 weeks) streptozocin (STZ)-induced diabetes on skeletal muscle vascular transport capacity. Vascular transport capacity was determined from measurements of pressure-flow relationships, capillary filtration coefficient, and permeability-surface area product (PS) for 51Cr-EDTA in isolated perfused hindquarters of control (n = 7) and diabetic (n = 6; 65 mg/kg STZ intraperitoneally) rats. Hindquarters were perfused with Tyrode's solution containing albumin (5 g/dl) and horse serum (10% vol/vol) and were maximally vasodilated with papaverine (30 mM). Hindquarters of diabetic rats weighed 42% less than control rats (86 ± 3 vs. 147 ± 4 g; P ≤ 0.001) because of profound muscle atrophy. Total hindquarters flow (ml · min−1 · 100 g−1) was greater in diabetic rats (P < 0.001) at perfusion pressures between 23 and 75 mmHg, indicative of an increased flow capacity relative to control rats. However, absolute flows (ml/min) were not different between control and diabetic rats. Neither capillary filtration coefficient (control = 0.0243 ± 0.0010 and diabetic = 0.0297 ± 0.0024 ml · min−1 · mmHg−1 · 100 g−1) nor isogravimetric PS (control = 3.91 ± 0.31 and diabetic = 4.39 ± 0.46 ml · min−1 · 100 g−1) were different in control and diabetic rats. However, absolute values for capillary filtration coefficient (ml · min−1 · mmHg−1) and PS (ml/min) were less in diabetic rats. These results indicate that muscle atrophy in rats with STZ-induced diabetes is accompanied by a proportional reduction in absolute exchange capacity for water (capillary filtration coefficient) and small solutes PS, such that microvascular exchange capacity per tissue mass is maintained at control levels. In contrast, absolute flow capacity is unchanged in diabetic rats such that hindquarters flow capacity per tissue mass is increased, which results in a greater vascular transport capacity.
Enzyme-Linked Immunosorbent Assay Method for Human Autophosphorylated Insulin Receptor: Applicability to Insulin-Resistant States
Authors: Hagino Haruhiko , Shii Kozui , Yokono Koichi , Matsuba Hiroshi , Yoshida Masaki , Hosomi Yoichi , Okada Yumi , Kishimoto Miyako , Hozumi Toshiki , Ishida Yoshihiko , Kazumi Tsutomu , Nishimura Ryuichiro , Kasuga Masato , Baba Shigeaki
Published: September 2013

The insulin receptors from erythrocytes of 50 patients with non-insulin-dependent diabetes mellitus were tested for their ability to autophosphorylate. The assay was performed by a new enzyme-linked immunosorbent assay system that used monoclonal anti-insulin receptor antibodies absorbed to microtiter plates as a first antibody and polyclonal antiphosphotyrosine antibody as a labeled second antibody. By this assay, 3 patients were identified with defects in their insulin receptor kinase, although their defects appeared heterogeneous. Patient 1 had 85% less maximal autophosphorylation with a normal ED50 (1.6 × 10−9 M insulin). Patient 2, who had polycystic ovary disease, had a 49.2% decrease in maximal autophosphorylation of insulin receptors, and the ED50 was shifted to the right (5.6 × 10−8 M). Patient 3 with acanthosis nigricans had a normal maximal autophosphorylation, but the ED50 shifted to the right (2.9 × 10−8 M). The mechanisms for the diversity detected in this assay is not known, but this technique has sufficient specificity and sensitivity to be used to screen for insulin-resistant patients who have a lack of kinase activity.
Molecular Scanning of the Insulin Receptor Gene in Syndromes of Insulin Resistance
Authors: Krook Anna , Kumar Sudhesh , Laing Ian , Boulton Andrew J M , Wass John A H , O'Rahilly Stephen
Published: September 2013

Using the molecular scanning technique of single-stranded conformational polymorphism (SSCP), we have examined the exons encoding the insulin receptor gene in 26 patients with syndromes of insulin resistance. We found 27 variant sequences, 4 of which were mutations that altered an amino acid. One patient with the Rabson-Mendenhall syndrome was homozygous for a mutation in the extracellular alpha-subunit (Ser to Leu323), one type A insulin-resistant patient was heterozygous for Pro to Leu1178, and another type A insulin-resistant patient was heterozygous for a mutation in the COOH-terminus of the receptor (Arg to Gln1351). The previously reported, and probably functionally insignificant, variant Val to Met985 was detected in one patient. No missense or nonsense insulin receptor mutations were found in any patients whose insulin resistance was associated with gross obesity, lipoatrophy, or acromegaloid features. No missense or nonsense mutations were found in subjects with polycystic ovary syndrome or Syndrome X. Putting these findings in the context of other work in this field, we conclude that subjects with leprechaunism or Rabson-Mendenhall syndrome have a high probability of having a missense or nonsense insulin receptor mutation. Nonobese, nondysmorphic, severely insulin-resistant females with hirsutism, acanthosis nigricans, and menstrual disturbance (type A phenotype) have an intermediate probability of having this type of insulin receptor mutation. Although insulin receptor mutations have been occasionally described in other phenotypes of insulin resistance, the frequency of point mutations in the exons of the insulin receptor gene in patients with those phenotypes appears to be low.
Adverse Effects of Recombinant Human Insulin-like Growth Factor I in Obese Insulin-Resistant Type II Diabetic Patients
Authors: Jabri Nabeel , Schalch Don S , Schwartz Sherwyn L , Fischer Jerome S , Kipnes Mark S , Radnik Barbara J , Turman Nancy J , Marcsisin Victoria S , Guler Hans-Peter
Published: September 2013

Data from studies in diabetic rodents and evidence from clinical situations of severe resistance to insulin suggest that insulin-like growth factor I (IGF-I) is able to at least partly overcome insulin resistance. To assess the efficacy of recombinant human IGF-I in subjects with the most common form of insulin resistance, e.g., obese, type II diabetic patients, we administered recombinant human IGF-I (rhIGF) in doses of 120 and 160 μg/kg twice daily for 4–52 days to seven such individuals who had been treated previously with high doses of insulin (> 0.7 U·kg−1 · day−1). Four patients exhibited comparable or enhanced, whereas three had diminished, blood glucose control on rhIGF-I relative to that while on twice daily NPH insulin during the six-week control period. The occurrence of adverse effects in all patients compelled us to discontinue rhIGF-I administration before completing the 8-week treatment period. These adverse effects included edema primarily on the face and hands, mild weight gain, occasional dyspnea, bilateral jaw tenderness, arthralgias and myalgias, fatigue, tachycardia, flushing, orthostatic hypotension, and local burning at the injection site. We conclude that the frequency and severity of side effects associated with administering high-dose subcutaneous rhIGF-I to obese insulin-resistant diabetic patients make it an unacceptable therapeutic agent for these patients despite its ability to produce reasonable blood glucose control in ∼50% of them.
Relationship Between Retinal and Glomerular Lesions in IDDM Patients
Authors: Chavers Blanche M , Mauer S Michael , Ramsay Robert C , Steffes Michael W
Published: September 2013

Current knowledge regarding the concordance and discordance of the eye and kidney complications of diabetes is based on observations by ophthalmoscopy of retinal structural changes, which may be present at early stages of the disorder, and renal functional changes, which only become apparent at the later stages of the disease. For this reason we investigated the relationship between retinal structural lesions and quantitative measures of glomerular structure in patients with insulin-dependent diabetes mellitus (IDDM). Renal biopsies were evaluated using morphometric techniques, and retinopathy classification was determined by retinal fundus photography in 86 patients with IDDM: age 30.4 ± 7.3 years and duration of IDDM 18.9 ± 6.3 years (mean ± SD). Retinopathy score correlated with glomerular basement membrane width (r = 0.39, P = 0.0002), mesangial volume fraction (VvMes/Glom) (r = 0.35, P = 0.0009), surface density of the peripheral capillary wall (SvPGBM/Glom) (r = 0.34, P = 0.0013), and index of arteriolar hyalinosis (r = 0.36, P = 0.0008). Abnormalities in VvMes/Glom and SvPGBM/Glom were more pronounced in patients with both retinopathy and hypertension. Four of the 15 patients (27%) with either normal urinary albumin excretion (UAE) or low-level microalbuminuria had advanced retinopathy but normal VvMes/Glom. In conclusion, the presence of advanced retinal disease with or without hypertension in patients with IDDM indicates a greater likelihood of advanced nephropathy as evidenced by increased VvMes/Glom and decreased SvPGBM/Glom. However, marked discordance between retinopathy and nephropathy occurs, as illustrated by patients with normal UAE or low-level microalbuminuria, normal glomerular structural measures, and advanced retinopathy.
Troglitazone Prevents Glucose-Induced Insulin Resistance of Insulin Receptor in Rat-1 Fibroblasts
Authors: Kellerer Monika , Kroder Gerhild , Tippmer Stefanie , Berti Lucia , Kiehn Reinhard , Mosthaf Luitgard , Häring Hans
Published: September 2013

Troglitazone (CS045), a compound belonging to the thiazolidine diones, is being tested as a new oral antidiabetic agent. Evidence exists from animal studies and clinical trials with non-insulin-dependent diabetes mellitus patients that Troglitazone might reduce insulin resistance. The molecular mechanism of this effect is not understood. In this study, we investigated whether Troglitazone might interfere with the mechanism of glucose-induced insulin resistance. Several studies indicate that hyperglycemia reduces the kinase activity of the insulin receptor in different cell types. This effect is paralleled by translocation of several protein kinase C (PKC) isoforms, and it can be prevented by PKC inhibitors, which suggests that glucose-induced receptor desensitization is mediated by activation of PKC. We studied the effect of hyperglycemia on the insulin receptor kinase activity and its modulation by Troglitazone in rat-1 fibroblasts that stably overexpress the human insulin receptor. Before stimulation with insulin (10−7 M), cells were acutely exposed to hyperglycemic conditions in the absence or presence of Troglitazone (0.01–2 μ/ml). The insulin receptor was solubilized from a plasma membrane fraction or whole cell lysates, and proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotted against antiphosphotyrosine and anti-insulin receptor β-subunit (CT 104) antibodies. Acute hyperglycemia (25 mM glucose) induced a significant inhibition of the insulin receptor kinase (IRK) activity within 30 min (inhibition to 30 ± 12.5% of maximal insulin-stimulated β-subunit phosphorylation, n = 9, P < 0.01).The glucose-induced inhibition of the insulin receptor kinase could be antagonized by a preincubation of the cells with Troglitazone before addition of 25 mM glucose (72 ± 13.5% of maximal insulin-stimulated 3-subunit phosphorylation after 20–30 min of preincubation at a concentration of 2 μg/ml Troglitazone, n = 9, P < 0.01). In addition, Troglitazone is also able to reverse the inhibition of the insulin receptor kinase caused by a prior glucose incubation. In parallel with the decrease of the IRK activity, the phosphorylation of the insulin receptor substrate-1 (IRS-1) was inhibited (inhibition to 45 ± 11.8% of maximal insulin-stimulated IRS-1 phosphorylation, n = 4, P ± 0.01), and this inhibition also could be reduced by Troglitazone (84 ± 15.7% of maximal insulin-stimulated IRS-1 phosphorylation in the presence of 2 μg/ml Troglitazone, n = 4, P ± 0.01). Taken together, the data suggest that Troglitazone is able to prevent and reverse hyperglycemia-induced insulin resistance of the insulin receptor in rat-1 fibroblasts. This mechanism might be relevant for the in vivo activity of this compound.
Pancreatic Islet Blood Flow in the Rat After Administration of Islet Amyloid Polypeptide or Calcitonin Gene-Related Peptide
Authors: Svensson Annika M , Sandler Stellan , Jansson Leif
Published: September 2013

Anesthetized male Sprague-Dawley rats (350–400 g) were injected intravenously with either 0.1, 1, 15, or 25 nmol rat islet amyloid polypeptide (IAPP), 65 or 650 pmol rat calcitonin gene-related peptide (CGRP), or saline alone. IAPP at the two highest doses decreased the mean arterial blood pressure (BP), increased blood glucose concentrations, and decreased serum insulin concentrations. CGRP at both doses decreased the BP but did not affect the blood glucose concentrations. The blood flow to the whole pancreas, pancreatic islets, adrenal glands, colon, duodenum, liver, and kidney was measured with a microsphere technique 30 min after administration of IAPP and 3 min after injection of CGRP. The two higher doses of IAPP (15 and 25 nmol) markedly reduced the whole pancreatic blood flow, whereas the islet blood flow remained unaffected. This resulted in an increase in the fraction of whole pancreatic blood flow diverted through the islets from ∼ 10 to 17%. No blood flow changes in the pancreas or the islets were observed when 0.1 or 1 nmol IAPP was injected. CGRP at both doses caused a decrease in both whole pancreatic and islet blood flow. No changes in fractional islet blood flow were observed, despite similar effects on mean arterial BP as observed after IAPP injections. Neither adrenal, duodenal, colonic, hepatic, skeletal muscle, nor renal blood flow were significantly affected by any of the concentrations of IAPP used, whereas 650 pmol CGRP decreased both duodenal and colonic blood flow. We conclude that IAPP and CGRP have different effects on pancreatic islet blood flow and that IAPP may be of importance for islet blood flow regulation.
What β-cell Defect Could Lead to Hyperproinsulinemia in NIDDM?: Some Clues From Recent Advances Made in Understanding the Proinsulin-Processing Mechanism
Authors: Rhodes Christopher J , Alarcón Cristina
Published: September 2013

Pancreatic β-cell dysfunction is a characteristic of non-insulin-dependent diabetes mellitus (NIDDM). An aspect of this dysfunction is that an increased proportion of proinsulin is secreted, but an actual β-cell defect that leads to hyperproinsulinemia is unknown. Nevertheless, an impairment in β-cell proinsulin conversion mechanism has been suggested as the most likely cause. Insulin is produced from its precursor molecule, proinsulin, by limited proteolytic cleavage at two dibasic sequences (Arg31, Arg32 and Lys64, Arg65xs). Two endopeptidase activities catalyze this cleavage: PC2 and PC3. PC2 endopeptidase cleaves predominately at Lys64, Arg65, and PC3 endopeptidase cleaves at Arg31, Arg32. The recent identification and characterization of these endopeptidases has enabled a better understanding of the human proinsulin-processing mechanism. In particular, experimental evidence suggests that the majority of human proinsulin processing is sequential. PC3 cleaves proinsulin first to generate a proinsulin conversion intermediate that is the preferred substrate of PC2. Both PC2 and PC3 activities are influenced by Ca2+ and pH, but the more stringent Ca2+ and pH requirements of PC3 suggest it as the most likely enzyme to regulate proinsulin conversion, as well as initiate it. When an increased demand is placed on the proinsulin-processing mechanism by a glucose-stimulated increase in proinsulin biosynthesis, there is a coordinate increase in PC3 biosynthesis (but not in PC2). This supports PC3 as the key endopeptidase that regulates proinsulin processing. In this perspective, the current concepts of the enzymology and regulation of proinsulin conversion at a molecular level are reviewed. Then, several hypothetical points of β-cell dysfunction that might affect the proinsulin-processing mechanism and lead to hyperproinsulinemia are considered. Because the term NIDDM encompasses a wide variety of different disorders, any one or a combination of these possible points of β-cell dysfunction could result in hyperproinsulinemia for a certain subset of NIDDM
Time Courses of Changes in Hepatic and Skeletal Muscle Insulin Action and GLUT4 Protein in Skeletal Muscle After STZ Injection
Authors: Youn Jang H , Kim Jason K , Buchanan Thomas A
Published: September 2013

To determine the relative time courses of changes in peripheral and hepatic insulin action and skeletal muscle GLUT4 protein levels after a streptozotocin (STZ) injection in rats, we performed hyperinsulinemic (14–18 nM), euglycemic (7.5 mM) clamps in control (n = 8) and diabetic rats at 1 (n = 7), 3 (n = 8), 7 (n = 8), and 14 (n = 6) days after intraperitoneal STZ (65 mg/kg). Basal plasma glucose concentrations increased from 8.1 ± 0.2 mM in control rats to 23.5 ± 1.2 mM 1 day after STZ (P < 0.01) and remained constant thereafter. Basal plasma insulin levels were ∼ 35% of control levels in all STZ groups (P < 0.01). Insulin-stimulated whole-body glucose uptake decreased significantly as early as one day after STZ injection (P < 0.01), resulting predominantly from a decrease in whole-body glycolysis. Insulin action to suppress hepatic glucose output was normal on day 1 after STZ but impaired markedly on day 3 and thereafter (P < 0.01). Insulin-stimulated glucose uptake in individual skeletal muscles was not altered until day 7 after STZ, and the magnitudes of decreases in skeletal muscle insulin action on days 7 and 14 were not fully accounted for by the decreases in GLUT4 protein level measured from the same muscles. Our data indicate that there is a temporal hierarchy in the development of insulin resistance in STZ-induced diabetes. Insulin resistance is manifested initially (within one day) as a reduction in insulin-mediated glucose uptake and glycolysis in tissues other than skeletal muscle; available data suggest that the liver is a potential site of the initial reduction in insulin-mediated glucose uptake. Resistance of hepatic glucose output to suppression by insulin appears next, by day 3. Insulin resistance in skeletal muscle appears last (between days 3 and 7 after STZ administration), and the resistance in muscle cannot be fully accounted for by reduced GLUT4 expression.
Increased Renal Metabolism in Diabetes: Mechanism and Functional Implications
Authors: Körner Anna , Eklöf Ann-Christine , Celsi Gianni , Aperia Anita
Published: September 2013

The coupling between the Na+/glucose cotransporter and Na+-K+-ATPase (NKA) described for epithelial cells (1) prompted us to study in rats with streptozocin-induced diabetes the effect of increased tubular glucose load on tubular Na+ reabsorption, NKA-dependent O2 consumption (QO2), and NKA activity. Filtered glucose is mainly reabsorbed in the proximal tubuli via the phlorizin-sensitive Na+/glucose cotransporter. In this study, the diabetic rats had a significantly higher renal blood flow (RBF), glomerular filtration rate (GFR), and Na+ reabsorption than the control rats. Total renal QO2 as well as QO2 in cortical tissue, which consists mainly of proximal tubular cells, was significantly higher in diabetic than in control rats. The increase in tissue QO2 was entirely caused by increased NKA-dependent QO2. NKA activity, measured as rate of ATP hydrolysis, was increased in cortical tubular but not glomerular tissue from diabetic rats. Phlorizin treatment abolished the increase in NKA activity, Na+ reabsorption, and QO2, as well as the increase in RBF and GFR in diabetic rats. We conclude that diabetes is associated with increased renal O2 metabolism secondary to the increase in coupled Na+ reabsorption via the Na+/glucose cotransporter and NKA. The increased oxygen consumption might contribute to the hyperperfusion and hyperfiltration in the diabetic kidney.
Early Changes in Postprandial Insulin Secretion, Not in Insulin Sensitivity, Characterize Juvenile Obesity
Authors: Le Stunff Catherine , Bougnères Pierre
Published: September 2013

The development of hyperinsulinemia and insulin resistance, both common in adults with established obesity, was studied in 16 children, weighing 169 ± 8% ideal body weight who were 12.7 ± 0.4 years of age with obesity duration of 0.5–8.5 years and continuous weight gain in excess of normal, and compared with 11 age-matched normal children. Early in the evolution of obesity, insulin and C-peptide responses to a normal meal were increased by 76 and 80%. The first insulin peak was higher (613 ± 53 pmol/ml) than normal (413 ± 59 pmol/ml, P < 0.02) and occurred only 50 ± 7 min after onset of lunch versus 33 ± 11 min in normal children (P < 0.0005). Obese patients had a total of 3.0 ± 0.2 large insulin peaks within the 6-h period after the lunch versus only 1.5 ± 0.2 peaks in normal children (P < 0.0005). In contrast, fasting plasma insulin and C-peptide levels remained normal during the initial years of obesity, then increased progressively with duration (r = 0.73, P < 0.001) and degree (r = 0.59, P < 0.02) of obesity. Insulin sensitivity evaluated as the rate of glucose uptake during a three-step hyperinsulinemic euglycemic clamp was comparable in the obese (20 ± 1.5 mmol.m−2 · min−1) and the normal (21.7 ± 1.5 mmol.m−2 · min−1) children. Initially higher than normal in obese children, the maximal rate of glucose uptake decreased with both obesity duration (r = −0.67, P < 0.005) and children's age (r = −0.66, P < 0.005), indicating the progressive development of insulin resistance. No correlation was found with overweight (r = −0.17, NS). Fasting plasma insulin level and maximal glucose uptake were inversely related (r = −0.67, P < 0.005). During the first years of obesity, insulin concentrations corresponding to half-maximal glucose uptake remained comparable in obese (677 ± 51 pM) and normal children (654 ± 59 pM) and showed no changes with duration of obesity. In conclusion, an abnormal pattern of insulin response to meals is one of the earliest metabolic alterations characterizing the obesity syndrome, followed by the parallel, time-dependent development of fasting hyperinsulinemia and insulin resistance. These results support the primacy of a dysfunction or dysregulation of β-cell function in obesity of juvenile onset.
Nicotinamide Prevents Interleukin-1 Effects on Accumulated Insulin Release and Nitric Oxide Production in Rat Islets of Langerhans
Authors: Andersen Henrik U , Jørgensen Klavs H , Egeberg Jørn , Mandrup-Poulsen Thomas , Nerup Jørn
Published: September 2013

Nicotinamide (NA) prevents macrophage- and interleukin-1 (IL-1)-mediated β-cell damage in vitro as well as diabetes development in animal models of insulin-dependent diabetes mellitus (IDDM). IL-1 β-mediated inhibition of insulin release and damage to β-cells are associated with intracellular production of nitric oxide (NO) radicals. Therefore, we studied whether NA prevented IL-1 β-induced islet NO production, measured as nitrite release from isolated rat islets, and, if so, whether this action was associated with prevention of IL-1 β-mediated inhibition of insulin release. NA dose- and time-dependently inhibited and delayed IL-1 β-induced islet NO production. Light microscopy detected that 25 mM of NA protected against IL-1 β-induced islet damage. Five to 50 mM of NA dose-dependently reduced inhibition of accumulated islet insulin release induced by 150 pg/ml of IL-1 β. NA was not able to reverse the reduced ability of IL-1 β-treated islets to respond to an acute glucose challenge. NO or nitrite did not interact directly with NA, because NA did not reduce sodium nitroprusside-generated nitrite. No-synthase inhibition with L-arginine depletion abolished NO production but only partially reduced IL-1 β-induced inhibition of accumulated insulin release. Complete inhibition of IL-1 β effects could not be obtained by adding L-arginine analogues to L-arginine-depleted medium, indicating that an NO-independent action of IL-1 β on islet insulin release may exist. These results suggest a novel mechanism for NA-mediated protection of IL-1–induced P-cell damage via an inhibitory effect of NA on the formation of NO.
Effect of 15-Deoxyspergualin on Immediate Function and Long-Term Survival of Transplanted Islets in Murine Recipients of a Marginal Islet Mass
Authors: Kaufman Dixon B , Gores Paul F , Field M Jane , Farney Alan C , Gruber Scott A , Stephanian Edic , Sutherland David E R
Published: September 2013

15-Deoxyspergualin (DSG), a macrophage immunomodulatory agent, was used as a probe in a murine model of islet transplantation to examine 1) the significance of the nonspecific, macrophage-mediated effector arm of β-cell injury in recipients of a marginal mass of isologous islets by analyzing the duration of temporary posttransplant hyperglycemia, a parameter of immediate β-cell function; and 2) whether long-term (> 100 days) functional survival could be achieved in recipients of a marginal mass of allogeneic islets. A dose-response study of the number of islets required to ameliorate diabetes showed that 150 isologous islets per recipient resulted in a 75% incidence of cure at a mean of 39.2 ± 5.8 days posttransplant. DSG-treated (0.625 mg.kg−1.day−1 intraperitoneally) recipients of isologous islets demonstrated a significant (P < 0.01) reduction in the duration of temporary posttransplant hyperglycemia (16.8 ± 3.2 vs. 39.2 ± 5.8 days), and DSG-treated recipients of allogeneic islets demonstrated a significant (P < 0.03) improvement in the rate of achieving long-term functional survival (75 vs. 22% in untreated control animals). Finally, identical rates of islet engraftment were found among control animals and DSG-treated animals by measurement of tissue insulin content in transplanted specimens. The results are consistent with the hypothesis that DSG alters the duration of temporary posttransplant hyperglycemia and extends long-term functional survival in murine recipients of a marginal mass of islets, not by affecting the efficiency of islet engraftment, but by suppression of the inhibitory effects on β-cell function by nonspecific, macrophage mediators.
Molecular Model of Human β-Cell Glucokinase Built by Analogy to the Crystal Structure of Yeast Hexokinase B
Authors: Charles Robert St , Harrison Robert W , Bell Graeme I , Pilkis Simon J , Weber Irene T
Published: September 2013

Recent studies have shown that mutations in human β-cell glucokinase that impair the activity of this key regulatory enzyme of glycolysis can cause early-onset non-insulin-dependent diabetes mellitus (NIDDM). The amino acid sequence of human glucokinase has 31% identity with yeast hexokinase, a related enzyme for which the crystal structure has been determined. This homology has allowed us to model the three-dimensional structure of human glucokinase by analogy to the crystal structure of yeast hexokinase B. This model of human glucokinase provides a basis for understanding the effects of mutations on its enzymatic activity. Residues in the active site and on the surface of the binding cleft for glucose are highly conserved in both enzymes. Regions far from the active site are predicted to differ in conformation, and 10 insertions or deletions that range in size from 1 to 7 residues are located on the protein surface between elements of secondary structure. The model structure suggests that human glucokinase binds glucose in a similar manner to yeast hexokinase. The glucose-binding site contains a conserved aspartic acid, two conserved glutamic acids, and two conserved asparagines that form hydrogen bond interactions with the hydroxyls of the glucose similar to those observed in other sugar-binding proteins. Mutation of residues in the predicted glucose-binding site has been found to greatly reduce enzymatic activity. This model will be useful for future structure/function studies of glucokinase.
Chromosome 4q Locus Associated With Insulin Resistance in Pima Indians: Studies in Three European NIDDM Populations
Authors: Humphreys Phillippa , McCarthy Mark , Tuomilehto Jaakko , Tuomilehto-Wolf Eva , Stratton Irene , Morgan Ruth , Rees Alan , Owens David , Stengård Jari , Nissinen Aulikki , Hitman Graham , Turner Robert C , O'Rahilly Stephen
Published: September 2013

Markers on chromosome 4q have recently been shown to be associated with insulin resistance in Pima Indians, a population in which insulin resistance precedes and predicts the development of non-insulin-dependent diabetes mellitus (NIDDM). To examine whether genes in this region could play a major role in susceptibility to NIDDM in other populations, we have examined the allele frequencies of a trinucleotide repeat near the fatty acid–binding protein 2 (FABP2) gene on 4q28–31 in three European populations: Finnish, U.K. Caucasian, and Welsh. The U.K. NIDDM population was selected for insulin resistance by studying patients whose obesity-corrected fasting plasma insulin before treatment was above the 98th percentile. Seven alleles were detected. On cross-tabulation analysis, there were no significant associations between allele frequencies and glucose intolerance in any of the populations. Log-linear analysis of the results from all three populations suggested a moderately significant interaction of glucose tolerance status (normal versus diabetic) and the FABP2 allele (partial x2 = 24, df 6, P = 0.027). The parameter describing the interaction of allele A3 and glucose tolerance status was the only such parameter differing significantly from zero (z-score +2.003, P = 0.046). In both the Finnish and U.K. population, the A3 allele was found ∼ twice as frequently in NIDDM than in control subjects (Finnish control subjects, impaired glucose tolerance, and NIDDM: 12.2, 22.4, and 26.6%, respectively; U.K. control subjects and NIDDM: 7.8 and 14.6%, respectively). In the Finnish populations, no associations were found between FABP2 alleles and plasma insulin levels or with homeostatic model assessment (HOMA) estimates of β-cell function and insulin sensitivity. Specific comparison of those subjects with and without the A3 allele revealed no difference in fasting (47.4 [36–61.8] vs. 47.4 [39–57] pM, geometric means and 95% confidence interval, NS) and 2-h (288 [222.6–373.2] vs. 297 [252.6–349.2] pM, NS) insulin or in insulin sensitivity as assessed by HOMA (47.6 [32.3–70.3] vs. 50.5 [39.8–64.2]%, NS). Similarly, in the U.K. NIDDM population, no differences in clinical or metabolic characteristics were found between those with and those without the A3 allele. In summary, in three European Caucasian populations, there is no evidence for a major genetic influence of the FABP2 locus on the development of diabetes. The weak association of the A3 allele with diabetes does not appear to be because of an effect of this allele on insulin resistance.
Bis(maltolato)Oxovanadium(IV) Attenuates Hyperinsulinemia and Hypertension in Spontaneously Hypertensive Rats
Authors: Bhanot Sanjay , Bryer-Ash Michael , Cheung Anthony , McNeill John H
Published: September 2013

We previously reported that bis(maltolato)oxovanadium(IV) (BMOV), an organic vanadium complex, decreased plasma insulin concentrations in nondiabetic rats without affecting plasma glucose levels (McNeill JH, Yuen VG, Hoveyda HR, Orvig C: Bis(maltolato)oxovanadium(IV) is a potent insulin mimic. J Med Chem 35:1489–1491, 1992). In this study, chronic oral BMOV treatment was started in 6-week-old spontaneously hypertensive (SH) rats and their Wistar-Kyoto (WKY) controls, and the effects of the drug on insulin sensitivity, plasma insulin, and blood pressure (BP) were studied. BMOV (0.35–0.45 mmol.kg−1.day−1) caused a sustained reduction in plasma insulin (198 ± 6 vs. untreated 366 ± 13.2 pM, P < 0.0001) and systolic BP (149 ± 3 vs. untreated 184 ± 3 mmHg, P < 0.0001) in SH rats. No changes were seen in WKY rats (plasma insulin: treated 228 ± 4.8 vs. untreated 222.6 ± 3.6 pM, P > 0.05; BP: treated 134 ± 3 vs. untreated 134 ± 5 mmHg, P > 0.05). At 13 weeks of age, euglycemic clamps were performed in fasted, conscious, mobile rats. During low-dose insulin infusions (14 pmol.kg−1 · min−1) with concomitant somatostatin administration, neither hepatic glucose output nor total body glucose uptake differed between the untreated SH and WKY rats. Insulin sensitivity, expressed as steady-state glucose clearance per unit of plasma insulin, was higher in the untreated SH compared with the untreated WKY rats (2.1 ± 0.2 vs. 1.2 ± 0.1 ml.kg−1.h−1.pM−1 P < 0.002). BMOV further enhanced insulin sensitivity in SH rats (3.6 ± 0.4, P < 0.002 vs. untreated SH rats). In conclusion, 1) SH rats are hyperinsulinemic but not insulin resistant compared with WKY rats; and 2) BMOV caused concurrent decreases in plasma insulin and BP in SH rats, which suggests that hyperinsulinemia may contribute toward the development of high BP in the SH rat.
Lithium Increases Susceptibility of Muscle Glucose Transport to Stimulation by Various Agents
Authors: Tabata Izumi , Schluter Jane , Gulve Eric A , Holloszy John O
Published: September 2013

Lithium is thought to have an insulin-like effect on glucose transport and metabolism in skeletal muscle and adipocytes. However, we found that lithium had only a minimal effect on basal glucose transport activity in rat epitrochlearis muscles. Instead, lithium markedly increased the sensitivity of glucose transport to insulin, so that the increase in glucose transport activity induced by 300 pM insulin was ∼2.5-fold greater in the presence of lithium than in its absence. Lithium also caused a modest increase in insulin responsiveness. This enhancement of the susceptibility of the glucose transport process to stimulation was not limited to insulin, because lithium induced increases in the susceptibility of glucose transport to stimulation by contractile activity, hypoxia, a phorbol ester, and phospholipase C. Lithium also blunted the activation of glycogen phosphorylase by epinephrine. These effects were not mediated by inhibition of adenylate cyclase, because neither basal- nor epinephrine-stimulated muscle cAMP concentration was affected by lithium treatment. The effects of lithium on glucose transport and metabolism in skeletal muscle are strikingly similar to the persistent effects of exercise. These results support the possibility that lithium might be useful in the treatment of insulin resistance in patients with non-insulin-dependent diabetes mellitus.