bluuebunny/crossref_metadata_2025 huggingface dataset:
Reversal of Mesangial Enlargement in Rats With Long-standing Diabetes by Whole Pancreas Transplantation
Authors: Orloff Marshall J , Yamanaka Naoki , Greenleaf Glenn E , Huang Yan-Ting , Huang Da-Gang , Leng Xi-Sheng
Published: September 2013

An important unanswered question about clinical use of pancreas transplantation is: can pancreas transplants reverse or, at least, stabilize well-established lesions of insulin-dependent diabetes mellitus (IDDM)? To answer this question, we performed whole pancreas transplantations in 190 highly inbred rats 6, 9,12,15,18, and 21 mo after induction of diabetes mellitus (DM) with alloxan. We then studied the effect on renal mesangial enlargement (ME) for 24 mo after onset of DM by a quantitative morphologic technique in which camera lucida tracings of the mesangium were made at × 1250 and were analyzed using an electronic planimeter connected to a calculator/computer. A pretransplant kidney biopsy was obtained so that the rats served as their own controls. In addition, studies were performed for 28 mo in 57 untreated diabetic controls and in 55 nondiabetic controls. Monthly metabolic studies showed that whole pancreas transplantation maintained very tight, lifelong metabolic control of diabetes. Kidney sections obtained for 2 yr from diabetic controls and for 21 mo from diabetic rats before transplantation showed highly significant increases in total mesangial area, nuclear-free mesangial area, and percentage of glomerular area occupied by nuclear-free mesangial area. Pancreas transplantation consistently produced a highly significant reversal of well-established ME, regardless of when it was performed. In most instances, the mesangial area was reduced to a size smaller than that measured at 6 mo. ME, one of the hallmark lesions of diabetic glomerulosclerosis, was selected as the target lesion on which to test the effectiveness of pancreas transplantation because kidney disease is a very important cause of mortality and morbidity in IDDM, and because there is a striking similarity between diabetic kidney lesions of rats and those of humans. Our results demonstrate that whole pancreas transplants are very capable of reversing one of the main lesions of well-established diabetic nephropathy.
The Insulin Sensitivity Index in Nondiabetic Man: Correlation Between Clamp-derived and IVGTT-derived Values
Authors: Beard James C , Bergman Richard N , Ward W Kenneth , Porte Daniel
Published: September 2013

Although the minimal-model-based insulin sensitivity index (S1) can be estimated from the results of a simple 180-min intravenous glucose tolerance test (IVGTT), its relationship to widely accepted but technically more difficult clamp-based techniques has not been resolved in humans. Therefore we measured S1 by standard IVGTT, modified IVGTT, and clamp methods in 10 nondiabetic men with %IBW of 109 ± 12 (mean ± SD). In the euglycemic clamp studies, insulin was infused to bring insulin levels (IRI) from basal, 8 ± 4 μU/ml, to plateaus of 21 ± 5 and 35 ± 6 μU/ml. S1[clamp], measured as the increase in glucose (G) clearance per increase in IRI [δINF/(δIRI × G)], averaged 0.29 ± 0.09 ml/kg·min per μU/ml. In the IVGTT studies, 300 mg/kg G was given as an i.v. bolus, and G and IRI were measured for 180 min; in the modified (mod) IVGTT, tolbutamide (300–500 mg) was given i.v. 20 min after the G to observe the effect of an IRI peak on G removal after G level was free of initial “mixing” effects. The S1 estimated by computer did not differ significantly between standard [(6.9 ± 3.4) × 1O−4 min−1 per μU/ml] and modified [(6.7 ± 3.5) × 10−4 min−1 per μU/ml] tests, indicating no bias due to the differing insulin patterns and levels. There was a strong positive correlation between S1 (mod IVGTT) and S1(clamp): r = 0.84; N = 10; P < 0.002. The correlation between S1(standard IVGTT) and S1(clamp) was 0.54, suggesting the modified test is less “noisy” Nonetheless, in eight euglycemic women with a wider range of adiposity, S1(standard IVGTT) has been significantly correlated with %IBW (r = −0.72) and basal IRI (r = −0.84). The correlation between S1 measures by clamp and IVGTT methods provides one step toward validation of the minimal model for studies of insulin action in man.
The Limitations to and Valid Use of C-Peptide as a Marker of the Secretion of Insulin
Authors: Polonsky K , Frank B , Pugh W , Addis A , Karrison T , Meier P , Tager H , Rubenstein A
Published: September 2013

The accuracy with which the secretion rate of insulin can be calculated from peripheral concentrations of C-peptide was investigated in conscious mongrel dogs. Biosynthetic human C-peptide and insulin were infused intraportally and their concentrations measured in the femoral artery.

During steady-state infusions of C-peptide, the peripheral concentration changed in proportion to the infusion rate and the metabolic clearance rate (5.2 ± 0.3 ml/kg/min) remained constant over a wide range of plasma concentrations.

Application of a two-compartment mathematical model, in which the model parameters were estimated from analysis of C-peptide decay curves after intravenous bolus injections, allowed the intraportal infusion rate of C-peptide to be derived from peripheral C-peptide concentrations, even under non-steady-state conditions. Estimates of the intraportal infusion rate based on this model were 102.4 ± 2.6% of the actual infusion rate as it was increasing and 102.3 ± 5.5% of this rate as it was falling.

The peripheral C-peptide : insulin molar ratio was influenced by the rate at which equimolar intraportal infusions of C-peptide and insulin were changed. The baseline C-peptide : insulin molar ratio (4.1 ± 0.9) increased to peak values of 8.2 ± 0.6,10.3 ± 2.0, and 14.9 ±1.3 when the infusion rate was increased and then decreased rapidly. Peak values of only 5.7 ±1.2 were found if the intraportal infusion rate was changed slowly.

In conclusion: (1) under steady-state conditions the secretion rate of insulin can be calculated as the product of the peripheral concentration of C-peptide and its MCR; (2) under non-steady-state conditions, however, application of more complex mathematical models, such as the two-compartment model used in the present study, allows insulin secretion rates to be accurately calculated at discrete time points; and (3) under non-steady-state conditions the C-peptide:insulin molar ratio is influenced not only by the extent of hepatic insulin extraction but by other factors, including the rate of change of insulin secretion and the clearance rate of C-peptide. Changes in this ratio should therefore not be assumed to reflect changes in hepatic insulin extraction.
Relationship of Fat Distribution to Glucose Tolerance: Results of Computed Tomography in Male Participants of the Normative Aging Study
Authors: Sparrow David , Borkan Gary A , Gerzof Stephen G , Wisniewski Cynthia , Silbert Cynthia K
Published: September 2013

Computed tomography (CT) scanning was used to assess the relationship of glucose tolerance to fat distribution in men. Three cross sections [chest (including upper arms), abdomen, and thigh] were scanned in 41 men randomly selected from the Normative Aging Study, a longitudinal study of aging. Greater amounts of fat in the upper body and greater ratios of upperbody fat to lower-body fat were significantly correlated with higher 2-h serum glucose levels after adjustment for age and body mass index. In particular, intra-abdominal fat, a feature uniquely measured by CT, was a significant correlate of 2-h glucose. Largely parallel results were obtained when we compared a sample of male diabetic subjects (N = 8) with the male normal subjects from our random sample. This investigation demonstrates that body fat distribution, adjusted for overall degree of obesity, is a significant correlate of glucose tolerance even in a sample unselected for extremes Of physique.
Insulin-Dependent Diabetes Mellitus Is Associated With Genes That Map to the Right of the Class I RT1.A Locus of the Major Histocompatibility Complex of the Rat
Authors: Colle E , Guttmann R D , Fuks A
Published: September 2013

Previous studies have demonstrated that the presence of at least one u-haplotype of the rat major histocompatibility complex (MHC), RT1, is a necessary but not sufficient condition for the development of overt diabetes mellitus. The present studies were undertaken to determine which portion of the RT1 gene complex is necessary for the occurrence of diabetes. We crossed hooded diabetic rats (RT1 .AaBuDu) with PVGr8 rats (RT1 .AaBuDu). F1 animals were mated to give 82 F2 animals and backcrossed with the hooded diabetics to produce 41 backcross animals. Diabetes occurred in animals with all three possible RT1.A genotypes. The diabetes was similar to that seen in BB rats and in hybrid strains developed from them. An immunoregulatory defect was marked by decreased percentage of peripheral blood lymphocytes staining with w3/25 monoclonal antibody, by an increased percentage of peripheral blood lymphocytes binding a mouse ascites control protein, and by decreased responsiveness of peripheral blood lymphocytes to stimulation by conconavalin A. We conclude that the u-allele of the class I A-locus gene product is not necessary for susceptibility to the development of diabetes in the rat. Therefore, either genes coding for the class II products of the uhaplotype or genes in linkage disequilibrium with these genes and mapping to the right of the A locus provide the permissive condition. Furthermore, the data suggest, but do not prove, that the u-haplotype derived from a strain remote from the BB rat can confer this susceptibility to the development of diabetes. We can also demonstrate that neither the susceptibility to diabetes nor the presence of peripheral blood lymphocyte characteristics, which mark the immunoregulatory defect, segregates with albinism.
Growth and Hormonal Content of Human Fetal Pancreas Passaged in Athymic Mice
Authors: Tuch Bernard E , Grigoriou Samantha , Turtle John R
Published: September 2013

While the usefulness of the human fetal pancreas transplanted into diabetic humans has yet to be realized, its transplantation into nude mice has revealed some of its potential. In this animal the organ grows in size, during which time differentiation of its endocrine component and maturation of the insulinogenic response to glucose occurs. The results reported in this article expand these results by providing data on the weight and both the insulin and glucagon content of these passaged organs.

Human fetal pancreata of gestational age 14–19 wk were implanted subcutaneously (s.c.) in nude mice and maintained in vivo for 5–54 wk (absolute age 19–68 wk). The implants were then removed and their insulin and glucagon content determined. Both the weight of these implants and their insulin content were positively correlated with the absolute age of the tissue (weight: r = 0.61, P < 0.001; insulin content: r = 0.62, P = 0.0003). The glucagon content bore no relationship to the age. The maximum level of insulin extracted from 30 passaged human fetal pancreata was 0.8 U, a level far below the daily insulin requirements in adult humans. It is suggested that an explanation for this is the site of transplantation used. To compare the s.c. site with the renal subcapsular space, the explants of four fetal pancreata were evenly divided between these two sites. After 11–13 wk, the implants were removed. Those beneath the renal capsule were larger and contained a greater amount of insulin and glucagon than those transplanted s.c.

It is concluded that: (1) the human fetal pancreas implanted in the nude mouse grows and its insulin content increases with time, and (2) the renal subcapsular space is a better site for transplantation in these animals than a S.C. Site.
Basal Glucagon Replacement in Chronic Glucagon Deficiency Increases Insulin Resistance
Authors: Bajorunas Daiva R , Dresler Carolyn M , Horowitz Glenn D , McDermott Katherine , Jeevanandam Malayapa , Fortner Joseph G , Brennan Murray F
Published: September 2013

To evaluate the role of glucagon in insulin-mediated glucose metabolism, we studied four men and four women, ranging in age from 30–73 yr (mean ± SEM, 54 ± 5) who had undergone complete pancreatic resection for cancer or chronic pancreatitis 16–58 mo previously. The patients had undetectable C-peptide levels and established lack of biologically active 3500 mol wt glucagon. Euglycemic insulin clamp studies were performed with a 40 mU · m−2 · min−1 insulin infusion in the basal, post-absorptive, insulin-withdrawn state, before and during the last 3 h of a 72-h glucagon replacement-dose infusion (1.25 ng · kg−1 · min−1). In four patients, hepatic glucose production was determined by a primed-constant infusion of 3-[3H]glucose. Monocyte insulin-binding studies, pre- and postglucagon, were performed in all patients.

The 72-h glucagon infusion, resulting in mean plasma glucagon levels of 124 ± 7 pg/ml, caused a significant rise in the mean plasma glucose level (249 ± 8 versus 170 ± 13 mg/dl preglucagon) and a sixfold increase in mean 24-h glucose excretion. Both with and without glucagon, euglycemic hyperinsulinemia achieved identical and complete suppression of hepatic glucose production. The mean glucose utilization rate (4.70 ± 0.36 mg · kg−1 · min−1 preglucagon) was significantly decreased by glucagon replacement (3.83 ± 0.31 mg · kg−1 · min−1 P < 0.02). Mean glucose clearance was also diminished with glucagon (4.49 ± 0.32 versus 5.73 ± 0.45 ml · kg−1 · min−1 preglucagon, P < 0.02). After glucagon administration, no significant change in the percent specific binding of insulin to monocytes could be demonstrated. These data support a role of physiologic concentrations of glucagon in the modulation of peripheral tissue glucose utilization.
An H-2 Alloantiserum Preserves β-Cell Function in Mice Made Diabetic by Low-Dose Streptozocin
Authors: Bonnevie-Nielsen Vagn , Lernmark Åke
Published: September 2013

The pancreatic β-cell mass and function in C57BL/KsJ mice is markedly reduced the day after the last injection of five daily injections of a subdiabetogenic, 40 mg/kg, dose of streptozocin (STZ). In this study, we prepared an H-2 alloantiserum by injecting C57BL/6J mice (H-2b) with spleen lymphocytes from C57BL/KsJ (H-2d) mice. The alloantiserum given on five consecutive days, 5 h before each injection of STZ, did not prevent the initial β-cytotoxic effect of STZ detected by perfusion of the pancreas and subsequent morphometric analysis of in situ dithizone-perfused pancreas. However, 12 days after the first injection of STZ, total insulin release in response to D-glucose, total pancreatic insujin, and pancreatic glucagon was greater in the alloantiserum-treated mice compared with controls receiving normal mouse serum. It is concluded that an H-2 alloantiserum may protect the function and amounts of β-cells remaining after the initial five lowdose STZ injections.
Postreceptor Myocardial Metabolic Defect in a Rat Model of Non-Insulin-Dependent Diabetes Mellitus
Authors: Schaffer Stephen W , Seyed-Mozaffari Mahmood , Cutcliff Cathleen R , Wilson Glenn L
Published: September 2013

Hearts isolated from non-insulin-dependent diabetic rats were found to exhibit reduced rates of basal and insulin-stimulated glucose metabolism. Since tissue levels of fructose 1,6-bisphosphate are significantly reduced in the diabetic heart, it was concluded that phosphofructokinase may be inhibited. However, neither glycogen nor glucose 6-phosphate accumulated in the myocyte, indicating that the phosphofructokinase reaction was not a bottleneck diverting substrate away from glycolysis. The other major factor contributing to decreased glycolytic flux in the diabetic heart is the impairment in glucose transport. Both basal and insulinstimulated transport of 3-O-methyl-D-glucose was 30% less in the diabetic heart/While insulin sensitivity was unaltered in the diabetic rat, insulin responsiveness was decreased, indicating that the impairment in insulin-stimulated hexose transport was caused by a postreceptor defect. The net result of these abnormalities in glucose metabolism is a significant reduction in the rate of ATP synthesis by the diabetic heart.
Impaired Insulin Receptor Binding and Postbinding Defects of Adipocytes From Normal and Diabetic Pregnant Women
Authors: Hjøllund Elisabeth , Pedersen Oluf , Espersen Thorkil , Klebe Joachim G
Published: September 2013

To evaluate the relative contribution of insulin binding and postbinding defects of glucose utilization in peripheral tissue during normal and diabetic pregnancy, we have studied the in vitro insulin action of isolated adipocytes from eight nondiabetic pregnant women and nine pregnant women with insulin-dependent diabetes mellitus who were undergoing cesarian section. The pregnant women were compared with a matched group of normal nonpregnant women undergoing gynecologic surgery. Insulin binding to adipocytes measured at tracer insulin concentration was reduced by 45% (P < 0.01) in normal pregnant women and by 30% (P < 0.02) in pregnant women with diabetes. In contrast, no changes were found between the three groups in insulin binding to pure monocytes and erythrocytes.

The glucose transport system in fat cells from both groups of pregnant women was characterized by impaired maximal (P < 0.05) and half-maximal (P < 0.05) response to insulin. When fat cell glucose metabolism was studied, pregnant diabetic women exhibited decreased basal lipogenesis (P < 0.05) and decreased maximal responses of lipogenesis and glucose oxidation to insulin stimulation (P < 0.05). Similar but less pronounced abnormalities were seen in glucose metabolism of adipocytes from nondiabetic pregnant women.

In conclusion, both in late normal and diabetic pregnancy, insulin binding to adipocytes is significantly reduced and accompanied by decreased insulin sensitivity and reduced maximal insulin responsiveness of glucose transport and by impaired basal and maximally insulin-stimulated glucose metabolism.
Insulin and C-Peptide Levels After Oral and Intravenous Glucose: Contribution of Enteroinsular Axis to Insulin Secretion
Authors: Hampton S M , Morgan L M , Tredger J A , Cramb R , Marks V
Published: September 2013

Peripheral venous plasma insulin and C-peptide concentrations were measured in 10 healthy volunteers, given either 100 g glucose orally or sufficient intravenous (i.v.) glucose to produce similar glucose concentrations when measured in arterialized blood. The incremental areas under both the insulin and C-peptide curves were significantly increased after oral as compared with i.v. glucose administration by 229% and 138%, respectively. Arteriovenous plasma glucose differences were higher after oral glucose administration and were positively correlated with plasma insulin concentrations. Plasma gastric inhibitory polypeptide (GIP) and insulin concentrations were measured in seven healthy volunteers given oral glucose loads ranging from 25 to 200 g. Both the magnitude and duration of the GIP and insulin responses after oral glucose ingestion were dose dependent. These results suggest that the main cause of the increase in peripheral insulin levels after large oral carbohydrate loads is augmented insulin secretion rather than reduced hepatic extraction, indicating the possibility that an enteroinsular factor does exist, in accordance with the “incretin” concept. They also emphasize the need to document both arterial and venous glucose concentrations for the correct interpretation of experiments investigating glucose homeostasiS.
In Vivo Regulation of Liver and Skeletal Muscle Glycogen Synthase Activity by Glucose and Insulin
Authors: Kruszynska Y T , Home P D , Alberti K G M M
Published: September 2013

The regulation of liver and skeletal muscle glycogen synthase by plasma insulin and glucose has not been investigated in vivo at physiological blood glucose concentrations. We have,therefore, used the glucose clamp technique to investigate the effects of these variables independently in rats. Short-term streptozocin-(0.15 g/kg) diabetic animals were used in addition to normal rats to avoid endogenous insulin secretion during hyperglycemic clamps. In normal and diabetic animals, 3 h of hyperinsulinemia without change in blood glucose concentrations caused only a small increase in liver glycogen synthase activity (+ 34%), whereas hyperglycemic clamps at 6.0 and 10.0 mmol/L resulted in marked increases (+ 268 and +394% of basal, P < 0.001). Liver glycogen concentrations at the end of the clamps reflected these changes. In skeletalmuscle, glycogen synthase was increased by +58% by the euglycemic hyperinsulinemic clamp and was not increased significantly further by hyperglycemia. Similarly, muscle glycogen concentration increased with the 4.0-mmol/L clamp but during the hyperglycemic clamps was only raised more indirect proportion to blood glucose concentrations. The results confirm that blood glucose concentration is the major short-term regulator of glycogen synthase activity in the liver but that insulin is of prime importance in skeletal muscle.
Controlled Release of Insulin From Polymer Matrices: In Vitro Kinetics
Authors: Brown Larry , Siemer Linda , Munoz Christina , Langer Robert
Published: September 2013

A biocompatible system was developed that permits continuous release of biologicallyactive insulin from small polymer matrices. Powdered insulin particles were incorporated into an ethylene-vinyl acetate copolymer matrix. The presence of particulate insulin resulted in a matrixcomposed of tortuous channels and constricted pores through which release occurred. When aqueous release media permeated the matrix, the insulin dissolved and diffused slowly through this tortuous network. The large concentration of insulin within the matrix provided the driving force for release. Release kinetics from these insulin polymer matrices were enhanced by increasing the insulin solubility, the insulin powder particle size, the loading of insulin within the matrix, and the porosity of the matrix. Appropriate geometric design of the polymer matrix resulted in near-constant insulin release rates.
Diabetic Autonomic Neuropathy in BB Rat: Ultrastructural and Morphometric Changes in Parasympathetic Nerves
Authors: Yagihashi S , Sima A A F
Published: September 2013

Longitudinal electron-microscopic and morphometric studies of autonomie nerves containing predominantly parasympathetic fibers were undertaken in the spontaneously diabetic BB rat. Unmyelinated fibers of the diabetic vagus nerve and myelinated fibers of the penile nerve showed increased numbers of axonal glycogeno-somes and axonal sequestration. Morphometric examination of myelinated and unmyelinated fibers of the vagus nerve revealed diminished fiber size compared with age-matched control animals. The distal myenteric nerve showed marked degenerative changes, whereas no structural changes could be demonstrated in intra-myenteric ganglion cells. These changes are similar to those described previously in somatic nerves of this model but different from those seen in sympathetic nerves Of the diabetic BB rat.
Effects of Oral Hypoglycemic Agent Methylpalmoxirate on Exercise Capacity of Streptozocin Diabetic Rats
Authors: Young J C , Treadway J L , Fader E I , Caslin R F
Published: September 2013

The effect of the oral hypoglycemic agent methylpalmoxirate (methyl-2-tetradecylglycidate), a selective inhibitor of long-chain fatty acid oxidation, on the exercise capacity of diabetic rats was evaluated. Rats were made diabetic by injection of streptozocin (75 mg/kg i.p.). which was confirmed by 4+ glucosuria. Daily oral administration of 2.5 mg/kg for 5 days, or a single dose of 10 mg/kg, of methylpalmoxirate produced a slight, nonsignificant decrease in the ability of diabetic rats to perform strenuous exercise of an intensity that caused exhaustion in less than 30 min. The ability of diabetic rats to perform prolonged, moderately strenuous exercise of an intensity that could be maintained for more than 60 min was not affected by methylpalmoxirate treatment. Methylpalmoxirate normalized plasma glucose concentrations, with resting glucose levels reduced 71% compared with nontreated controls, and did not cause hypoglycemic during prolonged exercise to exhaustion. Hepatic glycogen content was significantly reduced in methylpalmoxirate-treated rats in the fed, resting state, and during exercise, suggesting that liver was forced to oxidize carbohydrate at the expense of carbohydrate storage. Blood ketone levels of methylpalmoxirate-treated rats were reduced by 82% at rest, and exercise-induced ketosis was prevented by drug treatment. Muscle glycogen concentration and the rate of muscle glycogen depletion during exercise were not altered by methylpalmoxirate. It appears that the liver is the major site of action of methylpalmoxirate in diabetic rats when given in low doses.
Insulin-Like Material in Parotid and Submaxillary Salivary Glands of Normal and Diabetic Adult Male Mice
Authors: Patel D G , Begum N , Smith P H
Published: September 2013

Acid-ethanol extracts of homogenates from the parotid and submaxillary salivary glands of normal and strep-tozocin-induced diabetic adult male mice were investigated for insulin-like material. Extracts of both the parotid and submaxillary glands contained insulin-like immunoreactivity. The values were 156 ± 72 ng/g wet tissue in the parotid and 104 ± 36 ng/g wet tissue in the submaxillary gland. Fractionation of this material on Sephadex G-50 (superfine) columns revealed a single peak conresponding to the elution volume of isotopically labeled insulin. Isolated fat cells were stimulated by these extracts to convert [14C]glucose to 14CO2. This effect was blocked by preincubation with anti-insulin serum. It was observed with the avidin-biotin immunocytochemical technique that both the parotid and submaxillary glands of adult male mice possess a population of cells containing an insulin-like material. After intraperitoneal injection of streptozocin there was a marked decrease of insulin-like material extractable from both the parotid and submaxillary glands. However, this β-cell cytotoxic agent did not completely destroy the salivary cells containing the insulin-like material. These data suggest that both the parotid and submaxillary salivary glands may be extrapancreatic sources of insulin in mice.
Potentiation by Glucose of Lipolytic Responsiveness of Human Adipocytes
Authors: Moussalli Colette , Downs Robert W , May James M
Published: September 2013

The effect of glucose on lipolytic regulation was studied in isolated human adipocytes. Glucose enhanced adipocyte glycerol release in the presence and absence of the β-adrenergic agent ritodrine by 150–200% of control rates. The glucose effect was maximal at just >1 mM glucose and could not be attributed to prevention of a time-dependent decline in lipolysis. Glucose not only increased lipolytic stimulation at each of several concentrations of ritodrine but also enhanced the sensitivity to stimulation at low concentrations of the agent. Ritodrine-stimulated lipolysis was inhibited by insulin by 50–60%; although glucose increased absolute rates of lipolysis, it did not affect the relative inhibition of lipolysis by insulin or the sensitivity to the hormone. In investigating a possible cause of the glucose effect on lipolysis, it was found that the addition of adenosine deaminase increased lipolytic rates in the absence of glucose and blunted the relative stimulation of lipolysis by glucose, the latter implicating extracellular adenosine in the mechanism of the glucose effect.
Effect of Acute Exercise on Insulin Generation of Pyruvate Dehydrogenase Activator by Rat Liver and Adipocyte Plasma Membranes
Authors: Begum Najma , Terjung Ronald L , Tepperman Helen M , Tepperman Jay
Published: September 2013

Groups of young adult rats with body weights of 125–135 g (group A) or 300–400 g (group B) were subjected to one bout of prolonged exercise to exhaustion on a treadmill and were studied 2 h postexercise. Liver glycogen levels were markedly depleted in the exercised rats. Adipocytes from group A exercised rats showed a significantly greater increase in pyruvate dehydrogenase (PDH) activity in response to insulin than those from sedentary controls. Incubation with insulin of liver part iculate fractions from exercised group A rats resulted in an increased production of a mitochondrial PDH activator compared with preparations from sedentary controls. The tissues of both exercised and sedentary group B rats were less responsive to insulin than those of the smaller rats. A significant effect of exercise on increased production of a PDH activator in response to insulin was found only in experiments in which adipocyte plasma membranes were coincubated with mitochondria and insulin. For group B rats exercise provided no significant enhancement of insulin activation of intact adipocyte PDH or stimulation of the production of a PDH activator by liver paniculate preparations. Insulin binding to fat cells was not affected by exercise. Group A rats made insulin resistant by a high-fat diet did not respond to exercise by significantly increasing the insulin stimulation of PDH activator by liver membranes. The enhancing effect of a single bout of exercise on insulin response was not readily demonstrable in rats resistant to insulin either in association with age and weight or with a high-fat diet. In insulin-sensitive, young adult rats a single bout of exercise to exhaustion increases the effect of insulin on adipocyte PDH activity and on the generation of PDH-stimulating activity by liver and fat cell membranes. A postbinding site is probably responsible for the exercise effect.
Retinopathy in Older Type II Diabetics Association With Glucose Control
Authors: Nathan David M , Singer Daniel E , Godine John E , Harrington Catherine Hodgson , Perlmuter Lawrence C
Published: September 2013

Non-insulin-dependent (type II) diabetics over the age of 55 comprise most of the diabetic population and are at considerable risk for the development of both macrovascular and microvascular complications. We studied the prevalence of retinopathy and its association with putative risk factors for its development in an elderly (55- to 75-yr-old) population of type II diabetics. Our cross-sectional analysis revealed that duration of diabetes and hemoglobin A1c (HbA1c) concentration were the two major predictors of the presence of retinopathy. Duration effect was seen after 10 yr of diabetes, whereas HbA1c effect was linear over its entire range. Hypertension, which has been reported to be a risk factor for microvascular disease in younger diabetic patients, was not associated with retinopathy in the older type II population. Multiple logistic regression analysis revealed that both the duration of diabetes and HbA1c remained significant independent determinants of retinopathy even after taking age and blood pressure into account. Our results support an etiologie role for metabolic control in the development of retinopathy in the elderly type II population.
Mechanisms of Nitrosourea-Induced β-Cell Damage: Alterations in DNA
Authors: LeDoux S P , Woodley S E , Patton N J , Wilson G L
Published: September 2013

The initial step in streptozocin (STZ)-induced β-cell toxicity has been hypothesized to be the alkylation of specific sites on DNA bases. The enzymatic removal of these lesions results in single-strand breaks that over-activate the nuclear enzyme poly(ADP-ribose) synthetase and critically deplete the cell of NAD. Our studies were performed to quantitatively evaluate the extent of DNA damage in β-cells and correlate this damage with toxicity. Monolayer cultures of neonatal rat β-cells were used to determine cytotoxicity and DNA damage after exposure to STZ or the aglycone N-methyl-N-nitrosourea (MNU). Toxicity in β-cells was determined by correlating morphological alterations observed by phase-contrast microscopy with decrements in immunoreactive insulin release. The extent of DNA damage was determined by alterations in nucleoid density and quantitation of N7-methylguanine formation. Toxicity tests revealed that STZ and MNU were not toxic at equimolar concentrations. Streptozocin was toxic at 10−3 M, whereas only mild toxicity was observed with MNU at 10−2 M. Surprisingly, however, at equimolar concentrations the two drugs caused comparable DNA-strand breaks as evidenced by their ability to shift the nucleoid migration ratio in neutral sucrose gradients. Additionally, quantitation of N7-methylguanine formation after exposure to equimolar concentrations of the drugs demonstrated that the two alkylated DNA to the same extent. These findings suggest that factors in addition to the activation of poly(ADP-ribose) synthetase must be responsible for the toxicity seen with STZ, because MNU at a nonlethal concentration is capable of causing comparable DNA damage.
Islet Secretory Granules Contain Cytochrome b561
Authors: Mackin R B , Jones D P , Noe B D
Published: September 2013

A cytochrome has been detected in secretory granules prepared from anglerfish islets of Langerhans. The heme moiety was determined to be of the b type, and the dithionite-reduced cytochrome exhibited an α-band maximum at 561 nm with an extinction coefficient of 13.8 mM−1 · cm−1. The protein was present at a concentration of 40 ± 4 pmol/mg of secretory granule protein. The cytochrome was found to be an integral membrane protein and to be reduced by ascorbic acid but not by NADH, NADPH, reduced glutathione (GSH), or succinate.

Because of the similarity to previously characterized secretory granule cytochrome b561's from neuroendocrine tissues, this cytochrome is also referred to as cytochrome b561. Although its function has not yet been elucidated, the apparent specificity for ascorbate suggests that it may be a component of the ascorbate-de-pendent peptidyl-glycine α-amidating monooxygenase system that functions in the amidation of islet hormones.
Differential Activities of Tolbutamide, Tolazamide, and Glyburide In Vitro on Rabbit Myocardial Membrane Ca2+-Transporting ATPase Activity
Authors: Warnick P R , Davis F B , Davis P J , Mylotte K M , Blas S D
Published: September 2013

At clinically achievable concentrations (10−9 to 5 × 10−6 M), tolbutamide and tolazamide are in vitro inhibitors of Ca2+-transporting ATPase activity in sarcolemma-enriched rabbit myocardial membranes (sulfonylurea ICM, 10−7 M). Thyroid hormone stimulation of this calcium pump-associated enzyme in vitro has been previously reported;5 in our study, this hormonal action was shown to be inhibited by tolbutamide and tolazamide. In contrast to these two sulfonylureas, glyburide (up to 5 × 10−6 M) had no effect on basal or thyroid hormone-stimulable Ca2+-ATPase activity in vitro. Studies of binding of radiolabeled purified calmodulin to heart membranes showed that tolbutamide and tolazamide inhibited this interaction, whereas glyburide had no effect on calmodulin binding. Addition of purified calmodulin (5–40 ng/μg membrane protein) to myocardial membranes incubated with 10−7 M tolbutamide or tolazamide restored Ca2+-ATPase activity and thyroid hormone responsiveness of the enzyme.

Inhibition by tolbutamide and tolazamide of myocardial sarcolemmal Ca2+-ATPase is a mechanism by which these two sulfonylureas may at least transiently raise resting sarcoplasmic Ca2+ concentration. This effect of sulfonylureas on Ca2+-ATPase is not expressed in the presence of the benzamide side chain of glyburide. The inhibitory action of certain sulfonylureas on Ca2+-ATPase is mediated by interference of the agents with the binding of calmodulin to cardiac membranes.
Impaired Glucose Homeostasis in Adult Rats From Hyperglycemic Mothers
Authors: Bihoreau M T , Ktorza A , Kinebanyan M F , Picon L
Published: September 2013

The purpose of our study was to investigate whether nondiabetic gestationai hyperglycemia during fetal life could have additional effects on glucose homeostasis and insulin secretion in the adult rat. Hyperglycemia without the main other metabolic disorders and vascular injuries associated with diabetes was produced in unrestrained pregnant rats by continuous glucose infusion during the last week of pregnancy. Control rats were infused with distilled water. Compared with controls, the newborns from hyperglycemic rats were hyperglycemic and hyperinsulinemic. When studied longitudinally up to 3 mo, they showed slightly but significantly increased basal plasma glucose levels and normal basal insulin concentrations compared with controls. Glucose tolerance and insulin secretion in response to a glucose load (0.5 mg/kg, i.v.) were altered: Plasma glucose values were more increased at 5 min and remained higher 90 min after glucose injection; incremental plasma insulin values and the insulinogenic indexes (ΔIRI/ΔG) were always lower in rats from hyperglycemic mothers than in controls. These alterations were more and more marked with advancing age (1–3 mo). These data show that gestationai hyperglycemia may lead to persistent impairment of glucose homeostasis and insulin secretion in the adult rat.
Excess of DR3/4 in Type I Diabetes: What Does It Portend?
Authors: Rubinstein P , Walker M , Ginsberg-Fellner F
Published: September 2013

The HLA-DR genotypes of 158 new type I diabetic probands from simplex families are compared with those of 43 multiply affected sibships. There were no significant differences in the gene frequencies of the insulindependent diabetes mellitus (IDDM)-associated alleles, DR3 and DR4, and whereas the DR3/4 heterozygotes were as frequent among simplex probands as among the first affected of multiplex sibships, subsequently affected sibs displayed lower frequencies of this genotype in this as well as in previously reported samples, indicating that the excessive risk associated with DR3/ 4 heterozygosity depends on the order of affection and thus on environmental factors. It is proposed that the penetrance of the susceptibility gene is enhanced by epistatic effects of this genotype and that this enhancement is strongest under conditions of low environmental liability. Thus, the excessive risk for DR3/4 individuals appears to depend on secondary interactions between DR and the environmental factors that trigger the onset of this disease and does not in itself indicate the existence of distinct susceptibility alleles in coupling with these genes, i.e., of genetic heterogeneity or overdominance.
Myofibrillar Protein Breakdown in Skeletal Muscle is Diminished in Rats With Chronic Streptozocin-Induced Diabetes
Authors: Goodman Michael N
Published: September 2013

Previous reports have suggested that insulin may not regulate the breakdown of myofibrillar proteins in skeletal muscle. To further test the role of insulin, insulinopenia was produced by treating rats with streptozocin. After treatment, protein breakdown in skeletal muscle was evaluated with the isolated prefused rat hindquarter preparation. After the inhibition of protein synthesis with cycloheximide, total and myofibrillar protein breakdown were assessed by measuring the release of tyrosine and 3-methylhistidine, respectively, in the perfused hindquarters of diabetic and agematched control rats. Streptozocin-induced (65 mg/kg) diabetes (3- to 28-day duration) resulted in hyperglycemia, hypoinsulinemia, hyperphagia, increased plasma lipid levels, arrested body and muscle growth, and increased urea and 3-methylhistidine excretion. Despite this, protein breakdown in skeletal muscle diminished. The release of 3-methylhistidine by the perfused hindquarters of diabetic rats decreased, whereas the release of tyrosine remained unchanged, suggesting that the breakdown of myofibrillar proteins was affected specifically. 3-Methylhistidine (unbound) levels in skeletal muscle of unperfused diabetic rats as well as in skin decreased, whereas they increased twofold in the gastrointestinal tract. More severe diabetes (125 mg/kg streptozocin), which resulted in ketoacidosis, augmented protein breakdown in muscle; however, this response was due to a marked fall in food consumption (it was also evident when control rats were pair fed). These data reinforce previous conclusions that insulin does not play a major role in the regulation of myofibrillar protein breakdown in skeletal muscle. They also suggest that food consumption per se and/ or lipid availability may modulate myofibrillar proteolysis independent of insulin secretion. Lastly, increased 3-methylhistidine excretion in diabetic rats appeared to be of gastrointestinal origin. Because of this, caution must still be exercised in the use of 3-methylhistidine excretion as an index of myofibrillar proteolysis in skeletal muscle.
Protein Sparing in Skeletal Muscle During Prolonged Starvation: Dependence on Lipid Fuel Availability
Authors: Lowell Bradford B , Goodman Michael N
Published: September 2013

Previous studies indicated that protein sparing in skeletal muscle during prolonged starvation depends on the availability of lipid fuels. To test this relationship further, fasted rats conserving protein were treated in vivo for 6–8 h with the antilipolytic agent nicotinic acid (NA) or with tetradecylglycidate (TDGD), an inhibitor of long-chain fatty acid oxidation. After treatment, protein synthesis and degradation in skeletal muscle were evaluated with the perfused rat hindquarter. NA treatment decreased plasma 3-hydroxybutyrate and free fatty acids and increased plasma urea and urine urea excretion, indicating increased breakdown of body protein. TDGD produced similar metabolic effects, except that plasma free fatty acids were markedly increased as a result of inhibition of fatty acid oxidation. NA and TDGD also decreased plasma insulin and increased plasma corticosteroid. Inhibition of lipid metabolism in vivo resulted in accelerated loss of protein from skeletal muscle due to decreased protein synthesis and increased protein breakdown. NA increased both total (i.e., tyrosine release) and myofibrillar (i.e., 3-methylhistidine release) protein breakdown, whereas TDGD increased the breakdown of only nonmyofibrillar proteins (i.e., 3-methylhistidine release by perfused hindquarter was not altered). These data indicate that lipid fuels may directly modulate protein metabolism in muscle during prolonged starvation and may prevent a rise in catabolic hormones. They also indicate that free fatty acids may directly attenuate the breakdown of myofibrillar proteins in muscle during prolonged starvation and that this may be unrelated to their oxidation.
Buffy Coat Transfusions in Early Type I Diabetes
Authors: Cavanaugh John , Chopek Michael , Binimelis Jaume , Leiva Alberto , Barbosa Jose
Published: September 2013

Fresh whole-blood buffy coats from American Red Cross volunteers were used to treat early type I diabetes. Attempts were made to adapt to human diabetic patients a protocol successfully used in prediabetic BB rats. Twenty-two type I diabetic patients (duration of disease <4 wk) were randomized to treatment or control groups; the treatment patients were given one buffy coat(∼0.6 × 109 T-lymphocytes) weekly for 5 wk. Plasma C-peptide (stimulated and unstimulated), insulin dose, and hemoglobin A1c were measured before and periodically after the treatment for 24 wk. The control group underwent the same studies. Although there were no significant differences for the parameters studied between the two groups, 2 of 12 patients in the treatment group underwent three complete (normal glycemia without insulin) temporary remissions. One of these patients was given a second course of transfusions after relapse from the first remission and developeda second complete remission that lasted 2 mo. No control patient had remissions during the 24-wk study.Although the future of adoptive immunotherapy in the treatment or prevention of diabetes is not known, several probable limitations of the current protocol, as discussed here, can explain the differences in results between this trial and the rodent studies.
Adoptive Transfer of Insulitis and Diabetes in Neonates of Diabetes-Prone and -Resistant Rats: Tissue Localization of Injected Blasts
Authors: Logothetopoulos John , Valiquette Nancy , MacGregor Donald , Hsia Terrence
Published: September 2013

Intravenous transfusion of concanavalin A-activated splenic cells from acutely diabetic BB or diabetic BB/hooded hybrid donor rats into 6- to 36-h-old neonate recipients of diabetes-prone and -resistant rat lines induced insulitis and in some severe diabetes. These effects were observed 10-20 days after the injection of the blasts. Focal lesions of insulitis were absent in neonates killed 1 and 3 days after the blast injection but were observed in neonates killed on the 5th and 8th day. As determined by autoradiography after the injection of [3H]thymidine-labeled blasts, numerous blast cells migrated and settled in various immature lymph nodes and in the spleen within 24 h after injection. Focal mononuclear infiltrations in the islets containing labeled and unlabeled cells were again observed on the 5th and 8th day but not on the 1st and 3rd day after injection. These experiments indicate that target-specific blasts undergo a short phase of proliferation and maturation in lymphoid organs of the recipients, before initiating the autoimmune process in the pancreatic islets. They further suggest that specific immune cells rather than humoral anti-islet antibodies are more likely to play the major role in this autoimmune animal model of diabetes.
Effect of IgG Subclasses on In Vivo Bioavailability and Metabolic Fate of Immune-Complexed Insulin in Lewis Rats
Authors: Arquilla Edward R , Stenger David , McDougall Brenda , Ulich Thomas R
Published: September 2013

The bioavailability, distribution, and metabolic fate of 125l-labeled insulin complexed to antibodies in guinea pig antiserum, purified guinea pig lgG1, lgG2, a mixture of lgG1 and lgG2, and homologous Lou/m rat antiserum were studied in inbred Lewis rats. 125l-insulin complexed to purified guinea pig lgG2 antibodies was rapidly cleared from the blood and sequestered in increasing amounts with time in the liver. Large amounts of the 125l-insulin complexed to guinea pig lgG1 antibodies remained in the blood for at least 30 min. The bioavailability of 125l-insulin bound to lgG1 and lgG2 antibodies was inhibited for at least 30 min because significantly less was available for rapid binding to insulin receptors on hepatocytes and renal tubular cells and its subsequent rapid degradation. The bioavailability of 125l-insulin was further decreased when bound to antibodies in native guinea pig antiserum or a mixture of lgG1 and lgG2 antibodies compared with the 125l-insulin complexed to either purified lgG1 or lgG2 antibodies alone. The 125l-insulin bound to antibodies in native guinea pig antiserum or a mixture of lgG1 and lgG2 antibodies was distributed invivo in a manner reflecting the relative concentrations of the lgG1 and lgG2 antibodies present. The bioavailability, distribution, and metabolic fate of 125l-insulin in immune complexes prepared with homologous Lou/m rat insulin antiserum was qualitatively similar to that observed with immune complexes prepared with guinea pig insulin antiserum. It appears that the Lewis rat can be used as an in vivo model to study the bioavailability, distribution, and metabolic fate of insulin bound to xenogenic or homologous insulin antibodies.