bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduced Sample Number for Calculation of Insulin Sensitivity and Glucose Effectiveness From the Minimal Model: Suitability for Use in Population Studies
Authors: Steil Garry M , Volund Aage , Kahn Steven E , Bergman Richard N
Published: September 2013

The FSIGT has been extensively applied to the minimal model of glucose kinetics to obtain noninvasive measures of SI. The protocol has been modified by the addition of a bolus tolbutamide or insulin injection 20 min after glucose. Although the modified protocol has improved the S, estimate, the method still requires a relatively large number of samples (n = 30). To reduce the total number of samples, we choose a sample schedule that minimizes the variance of the parameter estimates and the error in reconstructing the plasma insulin profile. With data from 10 subjects (BMI 30 ± 7 kg/m2; SI 0.9–10.2 × 10−4 min−1 · μU−1 · ml−1), a schedule consisting of 12 samples (0, 2, 4, 8,19, 22, 30, 40, 50, 70, 90, and 180 min) was obtained. Estimates of SI obtained from the reduced sampling schedule were then compared with those obtained with the full sampling schedule. In all 10 individuals, the SI estimates were almost identical. A second, much larger data base consisting of 118 modified FSIGTs performed in 87 subjects (67 men, 20 women; BMI from 19.6 to 40 kg/m2 for men and 26.7 to 52.5 for women; SI, from 0.35 to 14.1 × 10−4 min−1 · μU−1 · ml−1) was then used to independently assess the efficacy of the reduced sampling protocol. For this data base, the correlation between SI, which was calculated from the full versus the reduced sampling schedule, was 0.95. The mean relative deviation was –1.5% (not significantly different from zero), and the SD of the relative deviation was 20.2%. Relative deviation was defined as the percentage of difference between SI calculated from the full sample protocol and SI calculated from the reduced sample protocol. Thus, the reduced sampling schedule provides an unbiased estimate of a population's SI, and an individual estimate is generally within 20% of that obtained with the full sampling schedule. A similar analysis of SG showed that this parameter was equally well determined from the reduced compared with the full sample schedule.
The Effects of Differing Insulin Levels on the Hormonal and Metabolic Response to Equivalent Hypoglycemia in Normal Humans
Authors: Davis Stephen N , Goldstein Richard E , Jacobs Julie , Price Lynn , Wolfe Robert , Cherrington Alan D
Published: September 2013

The aim off this study was to determine if differing concentrations of insulin can modify the counterregulatory response to equivalent hypoglycemia in normal humans. Experiments were conducted in 9 normal, lean men, who had fasted overnight. Insulin was infused in two separate, randomized protocols so that steady-state levels of 486 ± 33 (low) and 3056 ± 236 pM (high) were obtained. Glucose was infused during both protocols to ensure that the rate of fall of plasma glucose (0.07 mM/min) and hypoglycemic plateau (2.8 ± 0.1 mM) were similar. Despite similar plasma glucose levels, EPI (8.7 ± 0.7 vs. 5.5 ± 0.7 nM), NE (3.3 ± 0.3 vs. 2.3 ± 0.2 nM), and cortisol (811 ± 36 vs. 611 ± 72 nM) significantly increased during high compared with low insulin infusion, respectively (P < 0.05). Glucagon, growth hormone, and pancreatic polypeptide levels increased briskly and significantly but were not different during the two insulin infusions. HGP rose significantly from 12.1 ± 0.3 to 18.1 ± 1.1 μmol · kg−1 · min−1 in response to the high insulin level (P < 0.05) but remained unchanged (12.1 ± 0.4 and 11.7 ± 1.4 μmol · kg−1 · min−1) in the presence of the low insulin level. GRa increased significantly during high insulin levels (3.4 ± 0.3 to 4.8 ± 0.7 μmol · kg−1 · min−1 P < 0.05) but remained at a basal rate (3.0 ± 0.3 to 2.7 ± 0.6 μmol · kg−1 · min−1) in the presence of low insulin levels. sBP and heart rate increased more during high insulin infusion (18 ± 5 vs. 6 ± 5 mmHg and 18 ± 4 vs. 7 ± 2 beats/min, respectively, P < 0.05). In summary, the 6-fold higher insulin level resulted in significantly greater increases in catecholamine and cortisol secretion, HGP, lipolysis, heart rate, and sBP despite equivalent hypoglycemia. We conclude that at moderate hypoglycemia, high doses of insulin can augment certain aspects of the counterregulatory response in normal humans.
Effect of STZ Administration on Islet Isograft and Allograft Survival in NOD Mice
Authors: Takayama Yutaka , Ichikawa Takeru , Maki Takashi
Published: September 2013

We examined the effect of a single STZ administration on subsequent islet isograft and allograft survival in NOD mice. Young prediabetic NOD mice were rendered diabetic by STZ administration and transplanted with islet isografts 8–11 days later. The earliest loss of islet function occurred on postgraft day 49. In sharp contrast, 15 of 16 isografts in spontaneously diabetic mice were destroyed within 17 days postgrafting. A comparison of the age of islet isograft destruction in STZ-induced diabetic NOD mice with the course of diabetes development in the NOD mouse colony clearly showed that STZ administration at the prediabetic stage led to a significant delay of diabetes onset in isografts. When STZ was given to overtly diabetic NOD mice, both islet isografts and allografts survived significantly longer than those in untreated, spontaneously diabetic NOD mice. However, the degree of prolongation induced by STZ was much smaller compared with that induced by ALS, a potent immunosuppressive reagent. In vitro mixed lymphocyte culture experiments showed that spleen cells of mice given STZ exhibited time-dependent reduction of their alloantigen reactivities. These results demonstrate that STZ, which is commonly used to induce diabetes in various experimental animals, also possesses an immunosuppressive property, although it is relatively weak compared with ALS.
Amplification of Insulin Secretion by Lipid Messengers
Authors: Turk John , Gross Richard W , Ramanadham Sasanka
Published: September 2013

D-glucose induces a rise in pancreatic islet β-cell cytosolic [Ca2+] by processes requiring both glucose metabolism and Ca2+ entry from the extracellular space, and this Ca2+ signal is thought to be critical to the induction of insulin secretion. Insulin secretagogues also induce phospholipid hydrolysis and accumulation of phospholipid-derived mediators in islets, including the lipid messengers DAG, nonesterified arachidonic acid, and arachidonate 12-LO products. This study offers the following viewpoints on potential roles of these lipid messengers in insulin secretion as working hypotheses: 1) the Ca2+ signal provided to the β-cell by D-glucose induces insulin secretion only in the context of amplifying background signals provided by the β-cell content of messengers including DAG; 2) muscarinic receptor agonists amplify glucose-induced insulin secretion in part by altering the β-cell content of DAG; 3) the Ca2+ signal provided by metabolism of D-glucose is amplified by the level of nonesterified arachidonic acid in β-cell membranes, which acts to facilitate Ca2+ entry; 4) metabolism of glucose induces accumulation of nonesterified arachidonate in beta-cells via activation of a recently identified ASCI-PLA2 enzyme, which may be a component of the β-cell fuel sensor apparatus; and 5) arachidonate 12-LO metabolites are potential candidates as adjunctive modulators of β-cell K+-channel activity.
Muscle Sympathetic Nerve Activity Is Reduced in IDDM Before Overt Autonomic Neuropathy
Authors: Hoffman Robert P , Sinkey Christine A , Kienzle Michael G , Anderson Erling A
Published: September 2013

Studies of heart-rate variability have demonstrated that abnormal cardiac parasympathetic activity in individuals with IDDM precedes the development of other signs or symptoms of diabetic autonomic neuropathy. To determine whether IDDM patients have impaired sympathetic activity compared with normal control subjects before the onset of overt neuropathy, we directly recorded MSNA. We also examined the effects of changes in plasma glucose and insulin on sympathetic function in each group. MSNA was recorded by using microneurographic techniques in 10 IDDM patients without clinically evident diabetic complications and 10 control subjects. MSNA was compared during a 15-min fasting baseline period and during insulin infusion (120 mU · m−2 · min−1) with 30 min of euglycemia. A cold pressor test was performed at the end of euglycemia. Power spectral analysis of 24-h RR variability was used to assess cardiac autonomic function. IDDM patients had lower MSNA than control subjects at baseline (8 ± 1 vs. 18 ± 3 burst/min, P < 0.02). MSNA increased in both groups with insulin infusion (P < 0.01) but remained lower in IDDM patients (20 ± 3 vs. 28 ± 3 burst/min, P < 0.01). In the IDDM group, we found no relationships between MSNA and plasma glucose, insulin, or HbA1c concentrations. BP levels did not differ at rest or during insulin. Heart-rate variability and the MSNA response to cold pressor testing in IDDM patients did not differ from those in healthy control subjects. IDDM patients had reduced MSNA at rest and in response to insulin. The lower MSNA is not attributable to differences in plasma glucose or insulin, but, rather, is most likely an early manifestation of diabetic autonomic neuropathy that precedes impaired cardiac parasympathetic control.
Methionine for Valine Substitution in Exon 17 of the Insulin Receptor Gene in a Pedigree With Familial NIDDM
Authors: Elbein Steven C , Sorensen Lise K , Schumacher M Catherine
Published: September 2013

INSR gene mutations have been described in multiple individuals with extreme insulin resistance, but the INSR gene has not been implicated in familial NIDDM. We previously have screened members of 18 familial NIDDM pedigrees for mutations in exons encoding the tyrosine kinase domain of the INSR gene (exons 13–21) by SSCP. That analysis initially detected only patterns consistent with silent polymorphisms, but on direct sequence analysis of exon 17 we detected a Met-for-Val substitution at position 985 in 1/18 pedigrees. We confirmed the substitution by sequence analysis of subcloned, PCR-amplified DNA from two pedigree members and by hybridization to labeled primers for the normal and mutant sequences. We did not find the mutation in any other individuals. Pedigree members were typed for presence or absence of the Met985 substitution by hybridization of PCR-amplified exon 17 DNA to allele-specific oligonucleotide probes, and typing was confirmed by segregation of INSR haplotypes and by SSCP analysis. The substitution was present in 3 NIDDM individuals in 3 generations, including a lean individual with onset at age 24. The substitution was present in only 50% of NIDDM siblings in generation 2, however. To determine the clinical effect of the Met985 substitution, we compared the 5 nondiabetic pedigree members who carried the mutation with the 9 nondiabetic pedigree members without the mutation and with 266 members of other pedigrees. Fasting and 1-h postglucose insulin levels were not different between carriers and noncarriers (fasting, 71.4 pM vs. 74.5 pM; 1-h, 381 pM vs. 354 pM), even after correction for age, sex, and BMI. Both 1- and 2-h postglucose load glucose levels were higher (P < 0.05) among carriers relative to noncarriers, however (1-h, 9.2 mM vs. 6.55 mM; 2-h, 6.1 mM vs. 5.5 mM). Carriers also had significantly higher glucose levels when compared with 266 members of other pedigrees, after correction for age, weight, and sex (P < 0.05). These data suggest that although the Met985 substitution does not result in severe insulin resistance and has low penetrance with respect to expression of the NIDDM phenotype, it may represent a modifying factor if multiple loci predispose to diabetes in this pedigree. The identification of additional predisposing mutations and prospective studies of this pedigree will clarify the role of this insulin receptor substitution.
mRNA Expression of Growth Factors in Glomeruli From Diabetic Rats
Authors: Nakamura Tsukasa , Fukui Mitsumine , Ebihara Isao , Osada Shiori , Nagaoka Isao , Tomino Yasuhiko , Koide Hikaru
Published: September 2013

Evaluations of glomerular mRNA levels encoding for PCNA, TNF-α, PDGF-A and -B chains, TGF-β, IGF-I, bFGF, and EGF were made at 4, 12, and 24 wk after injection of STZ in Sprague-Dawley rats. The mRNA levels for PCNA, TNF-α, PDGF-B chain, TGF-β, and bFGF increased with age in STZ-induced diabetic rats. At 24 wk after STZ injection, mRNA levels for PCNA, TNF-α, PDGF-B chain, TGF-β, and bFGF were increased 3.8-fold, (P < 0.01), 4.2-fold (P < 0.01), 4.0-fold (P < 0.01), 5.2-fold (P < 0.001), and 3.6-fold (P < 0.01), respectively, in the glomeruli of diabetic rats when compared with control rats. In contrast, mRNA levels for IGF-I, PDGF-A chain, and EGF were not altered in glomeruli from diabetic and control rats throughout the experimental period. Insulin treatment partially ameliorated the increase in mRNA levels for PCNA, TNF-α, PDGF-B chain, TGF-β, and bFGF in the glomeruli of diabetic rats. These data indicate that alterations in growth factor mRNA levels in glomeruli may be a manifestation of diabetic nephropathy, and that hyperglycemia or insulin deficiency may play a role in abnormal growth factor gene regulation.
The Effects of Perindopril and Triple Therapy in a Normotensive Model of Diabetic Nephropathy
Authors: O'Brien Richard C , Cooper Mark E , Jerums George , Doyle Austin E
Published: September 2013

The effect of the angiotensin-converting enzyme inhibitor, perindopril, on functional and structural parameters of diabetic nephropathy has been compared with triple therapy (hydralazine, reserpine, and hydrochlorothiazide) in normotensive, STZ-induced diabetic Sprague-Dawley rats. Animal groups included control rats, diabetic rats treated with perindopril, diabetic rats receiving triple therapy, and untreated diabetic rats. Treatment was continued for 32 wk. Blood pressure reduction and severity of diabetes, as assessed by body weight and glycemic control were similar with both drug regimens. A similar rise in plasma renin activity occurred in the two groups receiving antihypertensive drugs, whereas the perindopril but not the triple therapy group had suppressed plasma angiotensin-converting enzyme activity. No significant difference was observed in renal function among the four groups. Diabetes was associated with a progressive increase in albuminuria, but this rise was ameliorated by both perindopril and triple therapy. No significant difference was noted in albuminuria between triple therapy and perindopril-treated diabetic rats. Diabetes was associated with glomerular basement membrane thickening, mesangial expansion, and glomerular volume. No glomerular ultrastructural parameter was affected by antihypertensive drugs. No specific benefit of angiotensin-converting enzyme inhibition over triple therapy could be detected in this normotensive model of diabetic nephropathy.
Glucose-Induced Amplitude Regulation of Pulsatile Insulin Secretion From Individual Pancreatic Islets
Authors: Bergsten Peter , Hellman Bo
Published: September 2013

The insulin secretory response to glucose was studied in single pancreatic islets isolated from ob/ob mice and rats. The perfusate from an individual islet was collected during 18-s periods and analyzed for insulin with an ELISA technique. Increase of the glucose concentration from 3 to ≥ 5.5 mM resulted in pulses of insulin release often originating from the basal level and having a frequency of 0.4/min. Glucose regulation of insulin release from the individual islet was manifested by alterations of the amplitudes of the pulses but not of their frequency. It is concluded that the large amplitude oscillations of cytoplasmic Ca2+ known to occur in the pancreatic β-cells have their counterpart in pulses of insulin release and that glucose stimulation of the secretory activity may be the result of recruitment of more β-cells into an oscillatory state.
Genotoxic Agents Increase Expression of Growth Arrest and DNA Damage–Inducible Genes gadd 153 and gadd 45 in Rat Pancreatic Islets
Authors: Eizirik Decio L , Björklund Andreas , Cagliero Enrico
Published: September 2013

Pancreatic β-cells are able to repair themselves after some sublethal injuries in vitro. However, little is known of the nature of the repair mechanisms active in these cells. This study examined the expression of growth arrest and DNA damage–inducible genes gadd 153 and gadd 45 in pancreatic rat islets and in the clonal insulin secretory HIT-T15 cells. Rat pancreatic islets were exposed in vitro to the alkylating agents streptozocin or methyl methanesulfonate, or to the cytokine recombinant interleukin-1 β. Islet exposure to STZ or MMS reduced insulin release by 40–50% over the next 4 h, whereas exposure to rIL-1 β induced a 60% increase in insulin release over the same period. Both gadd 153 and gadd 45 mRNA were detectable in rat islets, and their levels were increased twofold after STZ exposure, whereas MMS induced a fivefold increase in gadd 153 and a twofold increase in gadd 45 mRNA. Islet exposure to rIL-1β did not affect the expression of gadd 153 or gadd 45. HIT cells exposed to STZ or MMS also exhibited an increased expression of both gadd 153 and gadd 45. Again, this increase in gadd mRNA was more marked after MMS exposure. Moreover, expression of both gadd 153 and gadd 45 after MMS exposure lasted for a longer period of time than after STZ treatment. The effects of MMS on the expression of both gadd genes were inhibited by actinomycin D, suggesting that transcription is necessary for acute gadd induction. As a whole, these data show that gadd 153 and gadd 45 are increased in pancreatic islets or HIT cells after exposure to alkylating agents. Gadd expression may be related to cellular adaptation or DNA repair or both after stress. Because islets are able to recover completely their function after MMS exposure but not after STZ exposure, the role of these gadd genes may be relevant in the repair of islet DNA damage.
Expression of Calcium Channel mRNAs in Rat Pancreatic Islets and Downregulation After Glucose Infusion
Authors: Iwashima Yasunori , Pugh William , Depaoli Alex M , Takeda Jun , Seino Susumu , Bell Graeme I , Polonsky Kenneth S
Published: September 2013

Recent studies have shown that two different voltage-dependent Ca2+ channels are expressed in pancreatic islets, the β-cell/neuroendocrine-brain and the cardiac subtypes. The effects of chronic hyperglycemia on the levels in pancreatic islets of the mRNAs encoding the α1-subunits of the β-cell and cardiac subtype Ca2+ channels were studied in rats made hyperglycemic by infusion of glucose for 48 h. A competitive reverse transcriptase-polymerase chain reaction procedure was used to obtain quantitative data on the levels of these two transcripts in islets obtained from individual rats. The quantitative polymerase chain reaction data indicate that the levels of mRNA encoding the α 1-subunit of the β-cell Ca2+ channel are 2.5-fold > those for the cardiac subtype. The levels of β-cell Ca2+ channel mRNA were 72.9% lower in the glucose-infused animals when compared with the saline-infused animals (P < 0.005) and those of the cardiac channel were 72.1% lower in the animals infused with glucose (P < 0.02). In contrast, glucose infusion resulted in a twofold increase in insulin mRNA levels and did not significantly alter levels of β-actin mRNA. In situ hybridization studies revealed that the mRNAs for these two Ca2+ channels are expressed at higher levels in normal rat islets than in the surrounding acinar tissue, which suggests that the observed changes in mRNA levels occur within cells of the pancreatic islet. To assess the possible functional consequences of this reduction in expression of mRNA for the Ca2+ channels, the insulin secretory responses of perfused pancreases to the Ca2+ channel agonist Bay K8644 were studied. In pancreases from glucose-infused animals, the relative incremental insulin secretory response to Bay K8644 was reduced, and a similar blunting of the acute response to glucose also was seen. In summary, the predominant voltage-dependent Ca2+ channels subtype expressed in islets under basal conditions and after glucose infusion is the β-cell form with lower levels of the cardiac subtype. Glucose infusion for 48 h results in a significant reduction in the mRNA levels for both the β-cell and cardiac subtypes, and this is associated with enhanced basal secretion but reduced responses to glucose and the Ca2+ channel agonist Bay K8644.
Retinoic Acid Receptor, Cytosolic Retinol-Binding and Retinoic Acid-Binding Protein mRNA Transcripts and Proteins in Rat Insulin-Secreting Cells
Authors: Chertow Bruce S , Blaner Wiliiam S , Rajan Nithya , Primerano Donald A , Meda Paolo , Cirulli Vincenzo , Krozowski Zigmunt , Smith Robin , Cordle Mary Beth
Published: September 2013

To define the mechanism of vitamin A action at the β-cell level, we tested for the presence of messenger RNA for retinoic acid receptors α, β, and γ; cytosolic retinol-binding protein; and cytosolic retinoic acid-binding protein in RINm5F cells, an insulin-secreting cell line, and determined whether cytosolic retinol-binding protein and cytosolic retinoic acid-binding protein are present in isolated purified normal rat β-cells. Northern blot analyses showed two transcripts of retinoic acid receptor α messenger RNA (3.8 and 2.4 kb), one transcript of retinoic acid receptor messenger RNA (3.8 kb), and one transcript of cytosolic retinol-binding protein (0.9 kb) in RINm5F cells. Ribonuclease protection assays also showed the presence of cytosolic retinol-binding protein and cytosolic retinoic acid-binding protein in RINm5F cells. Quantitatively, cytosolic retinol-binding protein levels were 0.10 ± 0.02 pg/micrograms total RNA. Using specific radioimmunoassays, normal isolated purified rat β-cells contained CRBP (19.2 ± 2.38) and cytosolic retinoic acid-binding protein (16 ± 0.53 ng/10(6) cells). The presence of message for retinoic acid receptors α and γ, cytosolic retinol-binding protein, cytosolic retinoic acid-binding protein, and the gene products of cytosolic retinol-binding protein and cytosolic retinoic acid-binding protein in insulin-secreting cells support a mechanism of vitamin A action and role for cytosolic and nuclear receptors at the β-cell level similar to that suggested in nonendocrine cells. The presence of nuclear retinoic acid receptor a. and 7 suggests that vitamin A may affect insulin secretion through gene expression in the β-cell.
Acetyl-L-Carnitine Corrects Electroretinographic Deficits in Experimental Diabetes
Authors: Lowitt Saul , Malone John I , Salem Angela , Kozak Wlodzimierz M , Orfalian Zaven
Published: September 2013

Acetyl-L-carnitine reduces the latencies of electroretinogram oscillatory potentials in healthy humans. The effect of acetyl-L-carnitine (50 mg · kg−1 · day−1) on the increased electroretinogram latencies found in rats with STZ-induced hyperglycemia of 3-wk duration was evaluated. The aldose reductase inhibitor sorbinil, which has been shown to normalize abnormal electroretinogram tracings associated with STZ-induced diabetes, was used as a positive control. Aldose reductase inhibitors are thought to lower tissue sorbitol while increasing myo-inositol. The electroretinograms of the STZ-induced diabetic rats in this study were abnormal; treatment with acetyl-L-carnitine as well as sorbinil significantly improved electroretinogram b-wave amplitude and decreased the latencies of oscillatory potentials 2 and 3. Acetyl-L-carnitine treatment of STZ-induced diabetic rats did not affect hyperglycemia or erythrocyte polyol pathway activity as reflected by erythrocyte sorbitol levels. In contrast, sorbinil did reduce elevated erythrocyte sorbitol levels. This suggests that the impaired electroretinograms associated with STZ-induced diabetes may not be caused solely by increased polyol pathway activity.
Repair of O6-Methylguanine in Rat Pancreatic β-Cells After Exposure to N-Methyl-N-Nitrosourea
Authors: Nelson J Wesley , Ledoux Susan P , Wilson Glenn L
Published: September 2013

Because of the possible involvement of O6-methyldeoxyguanosine as a cytotoxic and carcinogenic lesion in pancreatic β-cells, studies were undertaken to assess the ability of rat β-cells to repair this DNA lesion. Primary cultures of neonatal rat β-cells were shown to contain very low levels of O6-methylguanine-DNA-methyltransferase activity, the predominant mechanism for repairing O6-methyldeoxyguanosine in mammalian cells. However, using a 32P-endlabeling assay to measure O6-methyldeoxyguanosine in cells after exposure to N-methyl-N-nitrosourea, it was determined that rat β-cells repaired O6-methyldeoxyguanosine to a substantial extent over a 24-h period. To elucidate the mechanism of O6-methyldeoxyguanosine repair in the virtual absence of constitutive O6-methylguanine-DNA-methyltransferase expression, studies were performed to determine if O6-methylguanine-DNA-methyltransferase expression was enhanced in N-methyl-N-nitrosourea-treated β-cells. No increase in O6-methylguanine-DNA-methyltransferase activity was detected 24 or 48 h after exposure. However, Northern blot analysis showed a two- to threefold elevation in O6-methylguanine-DNA-methyltransferase messenger RNA levels in β-cells 12 and 24 h after N-methyl-N-nitrosourea treatment. This finding is the first demonstration of a change in O6-methylguanine-DNA-methyltransferase messenger RNA levels in a cell type with low constitutive activity.
Fluorescence Digital Image Analysis of Glucose-Induced [Ca2+]i Oscillations in Mouse Pancreatic Islets of Langerhans
Authors: Valdeolmillos Miguel , Nadal Angel , Soria Bernat , García-Sancho Javier
Published: September 2013

At intermediate glucose concentrations, [Ca2+]i (intracellular calcium) measured in single islets of Langerhans undergo oscillations that are caused by glucose-induced bursting of electrical activity. Using digital video imaging of fura-2–loaded islets, we have analyzed the spatial distribution of [Ca2+]i in response to the natural secretagogue glucose and the KATP channel blocker tolbutamide. When the glucose level is increased, [Ca2+]i first increases and then starts to oscillate with a synchronous pattern through the islet. The synchrony is maintained even during nonrhythmic oscillatory patterns. In the presence of tolbutamide, [Ca2+]i increases in all the islet regions, suggesting that the calcium signal is derived mainly from the β-cell population. These results demonstrate that the islets behave as a functional syncytium in response to stimulatory glucose levels, canceling out heterogeneities at the single cell level.
Insulin Does Not Induce the Hydrolysis of a Glycosyl Phosphatidylinositol in Rat Fetal Hepatocytes
Authors: Ruiz-Albusac Juan M , Zueco Jose A , Velázquez Esther , Blázquez Enrique
Published: September 2013

An inositol phosphoglycan that is the polar head group of a glycosyl phosphatidylinositol has been considered as a putative mediator of insulin action. To gain insight into the functions of this hormone during development, the relationships between insulin, insulin receptors, glycosyl phosphatidylinositol, and inositol phosphoglycan were studied. Glycosyl phosphatidylinositol was isolated and characterized in fetal liver as early as day 15 of intrauterine life. In isolated hepatocytes from fetal and adult rats labeled with [3H]glucosamine, [3H]galactose, or [3H]myo-inositol, these molecules were incorporated into glycosyl phosphatidylinositol. In hepatocytes labeled with [3H]glucosamine and then allowed to react with [1-14C]IAI, the [3H]glycosyl phosphatidylinositol was purified as the 14C-labeled amidinated lipid. Glycosyl phosphatidylinositol molecules from fetal and adult cells were sensitive to hydrolysis by a phosphatidylinositol-specific phospholipase C from B. cereus. The product of this hydrolysis inhibits the activity of a cAMP-dependent protein kinase, whereas this effect was abolished by nitrous acid deamination. In isolated hepatocytes from adult animals, an inverse correlation between extracellular insulin and the number of insulin receptors and the cellular content of glycosyl phosphatidylinositol was observed. However, in fetal hepatocytes insulin failed to reduce the glycosyl-phosphatidylinositol content when labeled either with [1-14C]isethionyl acetimidate or [3H]glucosamine, whereas insulin-like growth factor I produced a significant hydrolysis of glycosyl phosphatidylinositol. Fetal and adult hepatocytes were incubated with insulin or inositol phosphoglycan after which glycogen phosphorylase activities were determined. Inositol phosphoglycan mimicked the action of insulin on both forms of the enzyme from adult hepatocytes, whereas in fetal cells insulin did not change, and purified inositol phosphoglycan reduced the activities of glycogen phosphorylase. These findings suggest a dissociation between insulin receptor occupancy and the expected hormonal effects in fetal hepatocytes. This could be related to alterations at a postreceptor level.
Delayed Onset of Insulin Activation of the Insulin Receptor Kinase In Vivo in Human Skeletal Muscle
Authors: Freidenberg Gary R , Suter Stephen , Henry Robert R , Nolan John , Reichart Donna , Olefsky Jerrold M
Published: September 2013

During the infusion of insulin in vivo, the rate of activation of glucose disposal lags significantly behind the rate of increase in serum insulin levels. To determine whether this delay was related to transcapillary transport of insulin, we determined increments in serum insulin levels, glucose disposal rates (GDR), and insulin receptor (IR) kinase activity measured during continuous infusions of insulin (40 and 120 mU · m−2 · min−1) administered to 8 nondiabetic males; similar studies were done at 1,200 · m−2 · min−1 in 2 of the subjects. Half-maximal insulin levels were achieved at a mean of 4.9 and 7.2 min during the 40 and 120 mU · m−2 · min−1 clamps, respectively, with corresponding half-maximal GDR stimulation at a mean of 59 and 47 min. Unlike the rise in insulin levels, IR kinase activation was much slower with half-maximal activity occurring at ∼40–60 min in the 2 clamps. Thus, the rise in serum insulin levels in each clamp was much faster than the increment in either kinase activity or glucose disposal. Insulin infusion increased both IR kinase and GDR maximally ∼10-fold, with half-maximal stimulation at ∼3,600 and ∼700 pM, indicating spare kinase for glucose disposal. These results demonstrate that the delay in stimulation of glucose disposal by insulin is related to a rate-limiting step between the intravascular space and the cell-surface of skeletal muscle. This may involve delayed transendothelial transport of insulin.
Abnormal Insulin Secretion, Not Insulin Resistance, Is the Genetic or Primary Defect of MODY in the RW Pedigree
Authors: Herman William H , Fajans Stefan S , Ortiz Francisco J , Smith Marla J , Sturis Jeppe , Bell Graeme I , Polonsky Kenneth S , Halter Jeffrey B
Published: September 2013

Maturity-onset diabetes of the young (MODY) is a form of non-insulin-dependent diabetes mellitus (NIDDM) associated with autosomal-dominant inheritance. In the RW pedigree, MODY is associated with polymorphic DNA markers on chromosome 20q. To determine the early abnormalities of insulin action and insulin secretion in MODY, we studied nondiabetic members of the RW pedigree with and without the gene marker. Six nondiabetic marker-negative and 5 nondiabetic marker-positive members of the RW pedigree were studied, as were 4 diabetic marker-positive family members. Unrelated, young, healthy subjects served as comparison groups. Insulin action and insulin secretion were assessed with a frequently sampled intravenous glucose tolerance test. Insulin secretion was further assessed during constant glucose infusion by deconvolution of plasma C-peptide and by pulse analysis. The nondiabetic marker-positive group had normal sensitivity to insulin and unimpaired acute insulin response to intravenous glucose (AIRglu). However, the nondiabetic marker-positive group had decreased mean plasma C-peptide concentration and reduced absolute amplitude of insulin secretory oscillations during prolonged glucose infusion. These responses to prolonged glucose infusion were similar to those observed in the diabetic group. No alterations of insulin secretion were observed in the nondiabetic marker-negative family members. Deranged and deficient insulin secretion, and not insulin resistance, appears to be the genetic or primary abnormality that characterizes nondiabetic individuals who are predisposed to MODY in the RW pedigree. Prolonged glucose infusion studies may reveal qualitative and quantitative defects in insulin secretion not identified by the AIRgIu. Use of the AIRglu may not be able to exclude a primary β-cell defect in the pathogenesis of NIDDM.
The Cardiac Renin-Angiotensin System in STZ-Induced Diabetes
Authors: Sechi Leonardo A , Griffin Chandi A , Schambelan Morris
Published: September 2013

To determine the effect of diabetes on the cardiac renin-angiotensin system, we compared angiotensin II binding density and renin, angiotensinogen, and type 1 angiotensin II (AT1) receptor mRNA levels in hearts of Sprague-Dawley rats 14 days after the administration of streptozotocin (STZ), in vehicle-treated control rats, and in STZ-administered rats made euglycemic with insulin. Myocardial angiotensin II receptor density, determined using an in situ autoradiographic technique, was increased significantly in hyperglycemic diabetic rats in comparison with control rats and euglycemic diabetic rats (P < 0.01) as a result of an increase in both AT1 and AT2 (type 2 angiotensin II) subtypes. The myocardial AT1 receptor mRNA level, determined by slot blot hybridization, was also significantly greater in the hyperglycemic diabetic rats (P < 0.005). Neither plasma renin concentration nor cardiac renin or angiotensinogen mRNA levels differed among the three study groups. In an additional experiment, control and diabetic rats were infused with angiotensin II (200 ng · kg−1 · min−1 i.p. for 7 days) or vehicle. Plasma renin concentration decreased significantly, whereas no significant changes occurred in cardiac renin or angiotensinogen steady-state mRNA levels. As in the first experiment, levels of AT1 receptor mRNA were significantly greater in the diabetic rats. Thus, myocardial angiotensin II receptor density is increased in diabetic rats in association with an increase in steady-state AT1 receptor mRNA levels, an abnormality that appears to be independent of changes in the circulating renin-angiotensin system.
Insulin Receptor Signaling in Madin-Darby Canine Kidney Cells Overexpressing the Human Insulin Receptor
Authors: Yeh Tammie C , Roth Richard A
Published: September 2013

We have developed and characterized a line of Madin-Darby canine kidney (MDCK) cells overexpressing the human insulin receptor. The expressed receptor was found to be processed normally, and its intrinsic tyrosine kinase was determined to be functional from both in vitro and in vivo phosphorylation studies. The expressed receptor was able to mediate an insulin-stimulated increase in both anti-phosphotyrosine-precipitable and anti-insulin receptor substrate 1-precipitable phosphatidylinositol 3-kinase activity. Moreover, insulin-induced glycogen synthase activity was greater and more sensitive to insulin in the transfected cells than in the parental cells. Interestingly, insulin promoted tubule-like growth in cells overexpressing the insulin receptor but not in the parental cells. Another advantage of this cell system lies in its ability to polarize into distinct basolateral and apical membrane compartments. With the use of biotinylation and Western analysis, the expressed insulin receptor was found to be preferentially expressed in the basolateral membrane (fivefold greater) in comparison with the apical membrane. Therefore, MDCK cells overexpressing the insulin receptor represent a novel system to study not only the pathway of insulin signaling, but also this pathway in the context of cell polarity.
Active and Passive Mechanical Properties of Isolated Arterioles From STZ-Induced Diabetic Rats: Effect of Aminoguanidine Treatment
Authors: Hill Michael A , Ege Elizabeth A
Published: September 2013

Studies were performed to examine the effect of experimental diabetes (4–6 weeks duration) on both the passive elastic and active myogenic properties of isolated skeletal muscle arterioles. Studies were conducted on untreated streptozotocin (60 mg/kg)-induced diabetic rats and in similar rats treated daily with either amino-guanidine (25 mg/kg) or methylguanidine (25 mg/kg). First-order cremaster muscle arterioles were isolated, cannulated, and pressurized in the absence of intraluminal flow. Video microscopy was used to determine relationships between arteriolar diameter and intraluminal pressure both in the active and passive (0 mmol/l Ca2+−2 mmol/l EGTA superfusated) tes. The measurements were used to calculate active myogenic responses, arteriolar distensibility, and stress-strain relationships. Under passive conditions, arterioles from untreated diabetic animals appeared to be stiffer and less distensible compared with similar arterioles from control animals. Under active conditions, i.e., in the presence of extracellular Ca2+, arterioles from the untreated diabetic group showed impaired myogenic reactivity as evidenced by a significant (P < 0.001) reduction in the negative slope of the pressure-diameter relationship over a physiological range of intraluminal pressures. Chronic treatment with aminoguanidine prevented the diabetes-induced changes in the active and passive properties of the isolated arterioles while treatment with methylguanidine appeared ineffective. Vasodilator responses to topically applied acetylcholine (10−8 to 5 × 10−6 mol/l) were significantly impaired in diabetic animals irrespective of treatment with aminoguanidine. The data indicate that experimental diabetes is associated with a decreased passive distensibility, or stiffening, of skeletal muscle arterioles that, in addition, may contribute to impaired active myogenic responses.
Neural Dysfunction and Metabolic Imbalances in Diabetic Rats: Prevention by Acetyl-L-Carnitine
Authors: Ido Yasuo , McHowat Jane , Chang Katherine C , Arrigoni-Martelli Edoardo , Orfalian Zaven , Kilo Charles , Corr Peter B , Williamson Joseph R
Published: September 2013

The rationale for these experiments is that administration of L-carnitine and/or short-chain acylcarnitines attenuates myocardial dysfunction 1) in hearts from diabetic animals (in which L-carnitine levels are decreased); 2) induced by ischemia-reperfusion in hearts from nondiabetic animals; and 3) in nondiabetic humans with ischemic heart disease. The objective of these studies was to investigate whether imbalances in carnitine metabolism play a role in the pathogenesis of diabetic peripheral neuropathy. The major findings in rats with streptozotocin-induced diabetes of 4–6 weeks duration were that 24-h urinary carnitine excretion was increased ∼ twofold and L-carnitine levels were decreased in plasma (46%) and sciatic nerve endoneurium (31%). These changes in carnitine levels/excretion were associated with decreased caudal nerve conduction velocity (10–15%) and sciatic nerve changes in Na+-K+-ATPase activity (decreased 50%), Mg2+-ATPase (decreased 65%), 1,2-diacyl-sn-glycerol (DAG) (decreased 40%), vascular albumin permeation (increased 60%), and blood flow (increased 65%). Treatment with acetyl-L-carnitine normalized plasma and endoneurial L-carnitine levels and prevented all of these metabolic and functional changes except the increased blood flow, which was unaffected, and the reduction in DAG, which decreased another 40%. In conclusion, these observations 1) demonstrate a link between imbalances in carnitine metabolism and several metabolic and functional abnormalities associated with diabetic polyneuropathy and 2) indicate that decreased sciatic nerve endoneurial ATPase activity (ouabain-sensitive and insensitive) in this model of diabetes is associated with decreased DAG.
Regulation of Islet β-Cell Proliferation by Prolactin in Rat Islets
Authors: Brelje T Clark , Parsons Jonathan A , Sorenson Robert L
Published: September 2013

This study examined the effects of prolactin on β-cell proliferation in pancreatic islet of Langerhans. Insulin secretion and β-cell proliferation were significantly increased from neonatal rat islets cultured for 4 days in the presence of either 500 ng/ml ovine prolactin (oPRL) or rat prolactin (rPRL). These effects could be prevented by including anti-oPRL serum in the culture media. Although insulin secretion and β-cell proliferation were slightly higher during the first 24 h of exposure to rPRL, maximal response was observed after 4 days for insulin secretion and 6–10 days for β-cell proliferation. The initial mitogenic response of β-cell to rPRL occurred by the limited recruitment of nondividing β-cells into the cell cycle and by most daughter cells proceeding directly into additional cell division cycles. Subsequently, the maximal effect of rPRL on β-cell proliferation was maintained by a higher rate of recruitment of previously nondividing β-cells into cell cycle with only one fourth of the daughter cells continuing to divide. These observations are difficult to reconcile with the proposal that a limited pool of β-cells capable of undergoing cell division exists in islets. Instead, these observations suggest that individual β-cells are transiently re-entering the cell cycle and dividing infrequently in response to rPRL. In this case, the majority of the β-cells would not be expected to be in an irreversible Go phase. We also demonstrated that the effects of rPRL on β-cell proliferation occur at normal serum glucose concentrations and are affected by inhibitors of polyamine metabolism. Additional studies on the effects of rPRL on β-cells should provide important information on the regulation of β-cell proliferation during conditions of increased insulin demand.
Poly I:C Induction of α-Interferon in the Diabetes-Prone BB and Normal Wistar Rats: Dose-Response Relationships
Authors: Sobel Douglas O , Ewel Cynthia H , Zeligs Barbara , Abbassi Val , Rossio Jeffrey , Bellanti Joseph A
Published: September 2013

Although the administration of a fixed dose of the α-interferon (α-IFN) inducer, polyinosinic polycytidilic acid (poly I:C), accelerates the development of diabetes in DP-BB rats, no reports have characterized the dose-response relationship of poly I:C with serum alpha-IFN levels and the development of diabetes. This study examines the dose-response relationships of poly I:C with the induction of serum α-IFN and the development of diabetes in DP-BB and normal Wistar rats. Also tested in this study is the hypothesis that the lack of development of diabetes in poly I:C-treated normal Wistar rats is attributable to a deficient α-IFN response. Using poly I:C doses of 0.5, 1.5, 5, and 10 μ/g body weight, a direct dose-response relationship was observed in DP-BB rats with the serum α-IFN response. Moreover, all doses of poly I:C accelerated the onset of diabetes in BB rats. Serum α-IFN levels inversely correlated with time of onset of diabetes (P < 0.01). Also, BB rats with higher levels of serum α-IFN were associated with earlier onset of diabetes (P < 0.001). Poly I:C-induced serum α-IFN levels were significantly lower in diabetic than in nondiabetic BB rats. In normal Wistar rats, although all doses of poly I:C significantly increased serum α-IFN levels, diabetes was not induced. The results of this study indicate that poly I:C administration elevates serum α-IFN and accelerates the development of diabetes in BB rats at even very low doses. This finding in conjunction with the correlation of serum α-IFN with the onset of diabetes is consistent with a pathogenetic role of α-IFN. The absence of a diabetogenic effect of poly I:C in Wistar rats suggests that α-IFN alone cannot induce diabetes in this animal.
Protection Against Adoptive Transfer of Autoimmune Diabetes Mediated Through Very Late Antigen-4 Integrin
Authors: Burkly Linda C , Jakubowski Aniela , Hattori Masakazu
Published: September 2013

The very late antigen-4 (VLA-4) integrin expressed on the surface of lymphocytes and macrophages can regulate their migration to inflammatory sites as well as control cellular activation. The role of VLA-4 in the establishment of autoimmune diabetes is not easily predicted given the multiplicity of adhesion pathways and their differential use by various cell types. The contribution of VLA-4 to insulin-dependent diabetes mellitus was investigated by administration of VLA-4-specific monoclonal antibodies (MoAb) in an adoptive transfer model of disease in NOD mice. This study shows that VLA-4-specific MoAbs profoundly inhibit the development of diabetes with protection sustained by repeated MoAb exposure. Insulitis was completely inhibited during treatment and progressed to a severe degree once MoAb treatment was suspended, yet ∼40% of treated recipients failed to become diabetic during 1–2 months post-treatment. Although we cannot rule out depletion of a relatively minor subpopulation of cells by prolonged anti-VLA-4 MoAb exposure, this inhibition of diabetes onset by treatment with MoAbs to VLA-4 supports a dependence on VLA-4 for cellular functions leading to diabetes and demonstrates that a significant disease modifying effect can be mediated by targeting the VLA-4 integrin.
Microalbuminuria Precedes the Development of NIDDM
Authors: Mykkänen Leena , Haffner Steven M , Kuusisto Johanna , Pyorälä Kalevi , Laakso Markku
Published: September 2013

Several studies have indicated that insulin resistance, elevated blood pressure (BP), and dyslipidemia precede the onset of non-insulin-dependent diabetes mellitus (NIDDM). Little data, however, exist on the presence of renal disease in prediabetic subjects. We measured albumin excretion in a cross-sectional population study in subjects 65–74 years of age living in eastern Finland in relation to the risk of developing diabetes 3.5 years later. The prevalence of microalbuminuria (urinary albumin-to-urinary creatinine ratio ≥ 2 mg/mmol) was 1.3-, 1.8-, and 2.0-fold higher among subjects with impaired glucose tolerance (n = 242), newly diagnosed NIDDM subjects (n = 92), and previously diagnosed NIDDM subjects (n = 136), respectively, compared with subjects with normal glucose tolerance (n = 826). Nondiabetic subjects with microalbuminuria had multiple abnormalities in cardiovascular risk factors including elevated BP, high triglyceride concentration, high insulin concentration, and a low high-density lipoprotein cholesterol concentration, a cluster of risk factors typical for prediabetic individuals. The relationship between microalbuminuria and the incidence of NIDDM over the 3.5-year follow-up was studied in 891 subjects who were free of diabetes at baseline. Converters to diabetes (n = 69) had a higher prevalence of hypertension (68.1 vs. 54.4%, P < 0.05) and a higher prevalence of microalbuminuria (43.5 vs. 30.4%, P < 0.05) than nonconverters (n = 822). In logistic regression analysis, microalbuminuria predicted the development of NIDDM independently of BP level. However, after adjustment for plasma glucose and insulin levels at baseline, the difference in the prevalence of microalbuminuria between converters and nonconverters was not statistically significant. These results suggest that microalbuminuria may be a feature of the prediabetic state and that the increase in albumin excretion rate may be related to increases in glucose and insulin concentrations.