bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of Glucose Metabolism in Pancreatic Islets
Authors: Trus Michael D , Zawalich Walter S , Burch Pamela T , Berner Donna K , Weill Victoria A , Matschinsky Franz M
Published: September 2013

We evaluated the possible role of islet glucokinase in controlling the rate of islet glucose metabolism, and thereby the rate of glucose-induced insulin release. The activities of glucokinase, hexokinase, P-fructokinase, and glyceraldehyde-P dehydrogenase were quantitated in sonicated or isotonically homogenized islet preparations using pyridine nucleotide-dependent fluorometric assays. In sonicates, about ¼ of the islet glucose phosphorylating activity was due to an enzyme with kinetic properties similar to glucokinase; % of the activity was due to hexokinase. The procedure for determining islet glucokinase activity was improved by centrifuging isotonic islet homogenates at 12,000 × g. The supernatant fraction was enriched for glucokinase. About ½ of the glucose phosphorylating activity in this fraction was due to glucokinase and ½ was due to hexokinase. The glucokinase activity in islet homogenates was ⅓ of the activity of hexokinase, V40 of the activity of P-fructokinase, and 1/400 of the activity of glyceraldehyde-P dehydrogenase. Detailed concentration dependency curves of glucose and mannose utilization were also obtained with intact isolated pancreatic rat islets. Glucose and mannose usage in islets was governed by two superimposed hyperbolic systems differing in Km and Vmax. A high Km system (Km for glucose 11 mM and for mannose 21 mM) predominated. A low Km system (Km for glucose 215 and for mannose 530 μM) contributed about 15% to the total activity. The available data with intact islets could be rationalized by the existence of two distinct hexose phosphorylating enzymes with differing capacities and kinetic properties. These enzymes, tentatively identified as glucokinase and hexokinase, could coexist in the same cell or could be distributed among different cell types. The possible physiologic significance of these results is discussed,emphasizing the idea of dual control of glycolysis and insulin release by glucokinase and hexokinase. An earlier proposal that glucokinase serves as glucoreceptor of β-cells [J. Biol. Chem. 243:2730 (1968] is greatly strengthened by the present studies.
Scope and Specificity of Acarbose in Slowing Carbohydrate Absorption in Man
Authors: Jenkins D J A , Taylor R H , Goff D V , Fielden H , Misiewicz J J , Sarson D L , Bloom S R , Alberti K G M M
Published: September 2013

Fifty-gram carbohydrate tolerance tests were performed on healthy volunteers to test the activity and specificity of an α-glucoside hydrolase inhibitor, acarbose (BAY g 5421). Two hundred milligrams acarbose reduced the area under the blood glucose response curve by 89% (P < 0.001) after sucrose, by 80% (P <0.002) after starch, by 19% (N.S.) after maltose, with no effect on glucose. Breath hydrogen measurements indicated an almost complete malabsorption of the sucrose. At 50 mg acarbose, some reduction in blood glucose and insulin response to sucrose was still seen, but no significant hydrogen production. It is suggested that at lower doses, acarbose may prolong the time course over which carbohydrate is absorbed as does dietary fiber; as with fiber, it may be a useful adjunct to diabetic therapy.
Sites of Action of Trifluoperazine in the Inhibition of Glucose-Stimulated Insulin Release
Authors: Janjic Danilo , Wollheim Claes B , Siegel Eberhard G , Krausz Yodphat , Sharp Geoffrey W G
Published: September 2013

Trifluoperazine, an inhibitor of calcium-calmodulin functions, was used in an attempt to understand the involvement of calcium-calmodulin in glucose-stimulated insulin release. Isolated rat pancreatic islets were used after a two-day period of maintenance in tissue culture. 45Ca2+ uptake and insulin release were measured during 5-min incubations. Dynamic insulin release and 45Ca2+ efflux were assessed during perifusion of the islets preloaded with 45Ca2+ during the culture period. Both phases of insulin release in response to 16.7 mM glucose were inhibited by approximately 60% in the presence of 10 μM trifluoperazine when the latter was added 35 min prior to high glucose. Stimulation of 45Ca2+ efflux by glucose was abolished. Glucose-stimulated 45Ca2+ uptake was inhibited by 43%. These results were compared with those of experiments in which depolarizing concentrations of potassium (24 mM) were used. Trifluoperazine inhibited K+-stimulated insulin release and 45Ca2+ uptake to a similar extent as that seen with glucose. Trifluoperazine did not appear to interfere with the inhibitory effect of glucose on 45Ca2+ efflux seen in the absence of extracellular Ca2+. Moreover, in Ca2+ deprived medium (with no possibility for Ca2+ uptake) insulin release in response to glucose + ouabain or in response to veratridine was also inhibited by trifluoperazine. It can be speculated that calmodulin is involved in the process by which glucose and potassium stimulate Ca2+ uptake, i.e., by activation of voltage-dependent Ca2+ channels in the plasma membrane. In addition, it appears that calmodulin is involved in the process by which glucose and veratridine act on stored calcium to raise the cytosolic Ca2+ concentration. Finally, trifluoperazine did not inhibit insulin release mediated by cyclic AMP (3-isobutyl-1-methyl-xanthine). Two conclusions may be drawn from this finding: (1) calmodulin may not be involved in the process of exocytosis per se and (2) cyclic AMP and glucose seem to mobilize stored calcium by different mechanisms.
The Influence of Genetic Background on the Expression of Mutations at the Diabetes Locus in the Mouse: III. Effect of H-2 Haplotype and Sex
Authors: Leiter Edward H , Coleman Douglas L , Hummel Katharine P
Published: September 2013

The expression of the mouse mutation, diabetes (db), was examined on eight different inbred genetic backgrounds. The influence of H-2 haplotype and sex was examined. Mice of both sexes in two diabetes (db) strains (C57BL/6J, 129/J) having the H-2b haplotype were resistant to the diabetogenic action of the mutant gene. On the contrary, two H-2d congenic diabetes stocks (C57BL/KsJ, DBA/2J) exhibited severe diabetes associated with beta-cell necrosis. However, diabetes resistance was not restricted to mice with H-2b haplotype since the congenic diabetes MA/J stock (H-2k) was also resistant. Similarly, diabetes susceptibility was not restricted to mice with the H-2d haplotype, since males, but generally not females, in the congenic CBA/Lt-db/db and C3HeB/FeJ-db/db stocks (both H-2k) also exhibited a severe diabetes. Males of the congenic SWR/J-db stock (H-2q) had a diabetes of intermediate severity. Female diabetes mice with H-2k and H-2q haplotypes exhibited a sustained hypertrophy and hyperplasia of beta-cells and were able to control hyperglycemia better than males. Thus, while the H-2b haplotype remains associated with resistance, and the H-2d haplotype with susceptibility to induction of genetic diabetes, the diabetes stocks with H-2k haplotype clearly illustrate the importance of non-H-2, but sex-associated, genetic modifiers.
Insulin-like Stimulatory Effect of Human Immunoglobulin G on Adipocyte Lipogenesis
Authors: Khokher M A , Dandona P , Janah S , Coulston G L
Published: September 2013

An investigation into the possible effect of thyroid stimulating immunoglobulin G on lipogenesis by adipocytes led to the discovery that all human IgGs exerted an insulin-like stimulatory effect on lipogenesis by rat adipocytes in vitro. Highly purified polyclonal IgGs prepared from normal subjects had stimulatory potencies similar to those of monoclonal IgGs obtained from patients with IgG myeloma. However, whole sera from myeloma patients with elevated IgG concentrations had a significantly higher stimulatory effect on adipocyte lipogenesis than control sera. These observations provide the first evidence that human IgG has an insulin-like metabolic effect, and that this effect is probably exerted by a nonspecific nonvariable portion of the IgG molecule. IgG may thus contribute to the non-suppressible insulin-like activity in the serum.
Oxytocin Infusion Increases Plasma Insulin and Glucagon Levels and Glucose Production and Uptake in the Normal Dog
Authors: Altszuler Norman , Hampshire Jennifer
Published: September 2013

Infusion of oxytocin (50-500 μU/kg/min) into normal conscious dogs produces a rise in plasma glucose, insulin, and glucagon levels. These changes are accompanied by a prompt increase in glucose production followed by an increase in overall glucose uptake, as determined using 6-3H-glucose infusion.
Serum Glycosidase Activity in Diabetes Mellitus
Authors: Merimee Thomas J , Kennedy Allan Laurence , Mehl Thomas D , Rosenbloom Arlan
Published: September 2013

The activity of three glycosidic enzymes, B-glucuroni-dase, N-acetylglucosaminidase, and B-galactosidase were measured in plasma samples from 163 diabetic subjects and 72 normal controls. No age- or sex-based variation in concentration was noted in controls. Plasma activity of B-glucuronidase and N-acetylglucosaminidase in diabetics correlated directly with the overall level of glycemia as measured by HbA1c levels. B-galactosidase activity was consistently normal in diabetics.

A significant age-based variation was noted in the diabetic group for B-glucuronidase and N-acetylglucosaminidase. Prior to age 12, B-glucuronidase and N-acetylglucosaminidase were normal in diabetics, but activity increased significantly after the age of 12, a change that appeared to coincide with the development Of puberty.
Preponderance of β-Adrenergic Binding Sites in Pancreatic Islet Cells of the Rat
Authors: Cherksey Bruce , Altszuler Norman , Zadunaisky Jose
Published: September 2013

Although the α- and β-adrenergic receptors have opposing effects on insulin secretion, the inhibitory influence of α-receptors appears to predominate. To determine if this was due to differences in number and affinity of receptors, isolated rat pancreatic islet cells were incubated with [3H]-dihydroalprenolol and [3H]-di-hydroergocryptine as ligands for β- and α-adrenergic binding sites. It was found that the number of β-adrenergic binding sites was 143 fmol/mg islet protein with a Kd = 0.57 nM. The number of α-adrenergic binding sites was 53 fmol/mg protein with a Kd = 0.26 nM. Thus, there are 2.7 times as many β-adrenergic binding sites as α-binding sites, and neither binding site number nor affinity is responsible for the predominant influence of the α-adrenergic receptors.
The Endothelium, Triglyceride-rich Lipoproteins, and Atherosclerosis: Insights from Cell Biology and Lipid Metabolism
Authors: Fielding Christopher J
Published: September 2013

Endothelial cells in culture retain many of the functional properties of the endothelium in vivo. At high cell density, they become contact-inhibited. Endothelial cells, like vascular smooth muscle cells and fibroblasts, express binding sites for low density lipoprotein when depleted of sterol. In contact-inhibited endothelial cells (but not actively growing cells), a block to internalization is evident, so that the cells bind but do not interiorize low density lipoprotein. Lipoprotein sterol does not enter the cell or regulate endogenous sterol synthesis. On the other hand, both contact-inhibited and actively growing endothelial cells express a separate receptor for triglyceride-rich lipoproteins. Cholesterol in these lipoproteins, unlike that in LDL, effectively regulates sterol synthesis in contact-inhibited endothelial cells and also mediates the accumulation of cholesterol in these cells. These findings are related to current concepts of atherogenesis. Receptors for triglyceride-rich lipoproteins may promote cellular sterol accumulation, release of contact inhibition in the surrounding endothelial cells, and exposure of the underlying vascular smooth muscle cells to plasma concentrations of both triglyceride-rich lipoproteins and LDL.
High Density Lipoproteins in Diabetes
Authors: Nikkilä Esko A
Published: September 2013

The concentration of high density lipoproteins (HDL) in patients with diabetes mellitus is highly variable. Subnormal HDL cholesterol levels are present in untreated patients with insulin-deficient juvenile diabetes, but the values return to the normal range after beginning insulin therapy. During conventional subcutaneous insulin treatment the diabetic patients often exhibit increased mean HDL cholesterol concentrations, even in the presence of poor diabetic control. HDL concentration is not related to blood glucose or fast hemoglobin levels. However, in the presence of overt ketoacidosis and upon development of advanced diabetic nephropathy, HDL levels fall. In noninsulin-dependent diabetes low HDL cholesterol values are common, but they are associated more with obesity and hypertriglyceridemia than with the diabetic state itself. Thus, when diabetic and nondiabetic subjects are compared at similar relative body weight and serum triglyceride levels, there seems to be no difference in the mean HDL cholesterol values. The possible effects on HDL of treatment by diet and particularly by oral antidiabetic agents are not yet clear; published results are controversial in this respect.

Alterations of HDL in diabetes are probably based on the presence of insulin deficiency or, more commonly, on hyperinsulinemia and insulin resistance. HDL (particularly the subfraction HDL2) concentration is regulated by two endothelial lipolytic enzymes, lipoprotein lipase and hepatic lipase, both of which are insulin sensitive. Peripheral hyperinsulinemia is produced in insulin-dependent diabetics by insulin treatment. This results in an increase of tissue lipoprotein lipase activity, which in turn augments HDL levels. In obese diabetic patients the peripheral tissues are resistant to insulin and, accordingly, the lipoprotein lipase activity is subnormal. Furthermore, the hepatic lipase activity is often increased and may contribute to the lowering of HDL by increased removal of HDL cholesterol. It is not known whether the alterations of HDL play any role in the increased atherosclerosis of diabetic patients.
Hypertension: The Major Risk Factor in Juvenile-onset Insulin-dependent Diabetics
Authors: Richard Christlieb A , Warram James H , Królewski Andrzej S , Busick Edward J , Ganda Om P , Asmal Abdul C , Stuart Soeldner J , Bradley Robert F
Published: September 2013

The prevalence of hypertension in various age groups of diabetics and its role as a risk factor in juvenileonset insulin-dependent diabetics followed for 40 yr after diagnosis was evaluated. The results show clearly that hypertension is more prevalent in diabetics of any age after age 24 yr than in the general population.

In this type of diabetes, although death due to renal disease occurs earlier than that due to coronary heart disease, both causes of death are significantly related to hypertension. Those patients with an onset of diabetes 13 yr of age or younger can expect to live longer following the diagnosis of diabetes mellitus than those with an onset after 13 yr of age, perhaps because hypertension appears at about the same age in both groups. Case/control analysis of the data shows that survivors have significantly less hypertension than those dying of renal or cardiac disease. Furthermore, the close temporal relationship between the onset of hypertension and the onset of proteinuria in patients with either renal or coronary deaths suggests that the hypertension in these patients is renal in origin.

Two other risk factors, smoking and serum lipids, were evaluated in this population. From the data thus far accumulated, neither smoking nor lipids appear to influence mortality significantly. We conclude that hypertension is the major additive risk factor for mortality in juvenile-onset insulin-dependent diabetics.
The Pittsburgh Insulin-dependent Diabetes Mellitus (IDDM) Registry: The Incidence of Insulin-dependent Diabetes Mellitus in Allegheny County, Pennsylvania (1965–1976)
Authors: LaPorte Ronald E , Fishbein Howard A , Drash Allan L , Kuller Lewis H , Schneider Barbara B , Orchard Trevor J , Wagener Diane K
Published: September 2013

An Insulin-dependent Diabetes Mellitus Registry has been developed in Allegheny County, Pennsylvania, through hospital record review and surveillance of pediatric practices. The yearly incidence ranged from 10/100,000 for nonwhite males to 16/100,000 for white males. There were no temporal trends in incidence for 1965–1976 nor major sex differences. Nonwhites had a slightly lower incidence, primarily in the younger age groups.
Pericyte Degeneration and Basement Membrane Thickening in Skeletal Muscle Capillaries of Human Diabetics
Authors: Tilton Ronald G , Hoffmann Phyllis L , Kilo Charles , Williamson Joseph R
Published: September 2013

Pericyte distribution and capillary dimensions were determined in tissue obtained at autopsy from human pectoral, abdominal, quadriceps femoris, and gastrocnemius muscle of 20 diabetics and 20 age- and sex-matched nondiabetics. Tissue was processed for electron microscopy, and morphometric data obtained from electron micrographs were used to calculate capillary circumference, the percentage of capillary circumference covered by pericytes, and capillary basement membrane width (CBMW). The numbers of vessels containing pericytes and the number of pericyte processes per vessel were tabulated as indices of pericyte distribution along capillaries. The presence of cellular debris within capillary basement membranes was tabulated as an index of pericyte necrosis.

Capillary circumference did not differ for controls and diabetics and did not vary between muscles from either group. CBMW was consistently thicker in diabetics than in controls and differences were greatest in lower extremity muscles. Pericytes were associated with virtually all vessels in lower extremity muscles of both normal and diabetic subjects. Although no differences were observed between controls and diabetics for each muscle examined, pericyte circumferential coverage of capillaries, as well as numbers of pericyte processes per capillary, increased significantly in the direction of head to foot for both controls and diabetics, paralleling increases in CBMW. Pericyte debris within capillary basement membranes also increased significantly in the direction of head to foot in both controls and diabetics and, in addition, occurred much more frequently in diabetics than in controls, with the greatest differences present in lower extremity muscles.

These observations indicate that pericyte frequency and coverage of capillaries vary between different skeletal muscles, but not between controls and diabetics. These findings, coupled with the increased frequency of pericyte debris within capillary basement membranes of diabetics, suggest that: (1) pericyte degeneration and turnover are increased in skeletal muscle capillaries of diabetics, arid (2) pericyte degeneration is not limited to the retina in diabetes mellitus. A strong correlation between the presence of pericyte debris and capillary basement membrane thickening suggests that both may be linked to a common pathogenetic factor.
The Renin-Angiotensin-Aldosterone System in Diabetic Patients with Hyperkalemia
Authors: Sunderlin Frederick S , Anderson Gunnar H , Streeten David H P , Blumenthal Stanley A
Published: September 2013

Seven long-standing diabetic patients with spontaneous and intermittent hyperkalemia were studied in an effort to assess the normality of their renin-aldosterone axis. The administration of oral glucose, in the absence of insulin, caused a paradoxical rise in serum potassium with no significant change in plasma aldosterone concentration from controls. All displayed subnormal aldosterone-secreting capacity to known stimuli of aldosterone secretion such as low salt diet, angiotensin II infusion, and ACTH infusion. The paradoxical rise in serum potassium with hyperglycemia was corrected in all by concomitant administration of insulin or pretreatment with a mineralocorticoid. Our observations question the role of aldosterone deficiency in the phenomenon of glucose-induced hyperkalemia.
Zinc-Induced Inhibition of Insulin Secretion from Isolated Rat Islets of Langerhans
Authors: Ghafghazi Taghi , McDaniel Michael L , Lacy Paul E
Published: September 2013

The present experiments indicate that ZnCl2 (0.015–0.50 mM) inhibits in a dose-dependent manner insulin secretion from isolated rat islets stimulated by D-glucose, L-leucine, and potassium. This inhibitory effect is partially reversed by washing and antagonized by high calcium concentrations in the medium. Zinc levels that inhibit insulin release do not affect 45calcium uptake, and zinc will not replace calcium in triggering insulin release. The conversion of 14C-D-glucose to 14CO2 by islets is not modified by zinc (0.12 mM or 0.50 mM) following either 2- or 0.5-h incubation periods, respectively. It is concluded that the inhibitory effect of zinc on insulin secretion may, in part, be mediated through interference with an intracellular function of calcium by the β-cell.
Pathogenesis of Hypoglycemia in Insulinoma Patients: Suppression of Hepatic Glucose Production by Insulin
Authors: Rizza Robert A , Haymond Morey W , Verdonk Carlos A , Mandarino Lawrence J , Miles John M , Service F John , Gerich John E
Published: September 2013

To determine the mechanism by which hyperinsulinemia causes hypoglycemia in insulinoma patients, rates of glucose production and utilization, and circulating levels of insulin, glucagon, alanine, lactate, and glycerol were measured in 6 insulinoma patients during development of fasting hypoglycemia and in 8 normal volunteers studied over an identical interval. Initially, insulinoma patients had a greater plasma insulin (42 ± 9 versus 15 ± 1 μU/ml) and glucagon levels (214 ± 31 versus 158 ± 21 pg/ml) than normal subjects, P < 0.05, but their plasma glucose levels (81 ± 4 mg/dl) and rates of glucose production and utilization (1.71 ± 0.08 and 1.74 ± 0.08 mg/kg min, respectively) were not significantly different from those of normal subjects (93 ± 2 mg/dl, 1.93 / 0.11, and 1.92 ± 0.13 mg/kg · min, respectively). During a subsequent 8-h fast, glucose production and glucose utilization decreased in both groups, but more markedly in insulinoma patients. Since glucose utilization exceeded glucose production to a greater extent in insulinoma patients than in normal subjects, plasma glucose decreased to 44 ± 3 mg/dl in insulinoma patients, but only to 84 ± 1 mg/dl in normal subjects (P < 0.001). Glucose utilization in insulinoma patients never exceeded that of normal subjects. These results demonstrate that fasting hypoglycemia in the insulinoma patients is usually due to suppression of glucose production rather than to acceleration of glucose utilization, as is widely thought. A direct effect of insulin on the liver is probably responsible, since circulating levels of gluconeogenic precursors are normal and since plasma glucagon increases during development of hypoglycemia in insulinoma patients.
The Effect of Antisera to Insulin, 2-DeoxygIucose-Induced Hyperglycemia, and Starvation on Wound Healing in Normal Mice
Authors: Weringer Elora J , Kelso John M , Tamai Irene Y , Arquilla Edward R
Published: September 2013

Wound healing was examined in normal C57B/6 male mice treated with antiserum to insulin or 2-deoxyglucose (2-DG) and in mice starved for 33 h. Hyperglycemia was induced after antiserum or 2-DG treatment; the blood glucose was lowered in the starved mice when compared with controls. Small dermal wounds were made in the ears of the mice 1 h after the initial injection of antisera or 2-DG. the starved group were wounded after 25 h of fasting. All animals were biopsied 8 h later. The wounds were examined by light microscopy and wound components (capillaries, fibroblasts, PMNs, collagen, and edema) were quantitated by lineal point analysis. Mice treated with antisera to insulin and mice starved for 33 h had an impaired healing response; the mice treated with 2-DG had a response similar to controls. These results suggest that hyperglycemia, per se, or the production of any toxic metabolites from high blood glucose levels could not alone induce the poor healing response. The depressed response in the antiserum-treated and starved mice may be due to the decreased availability of insulin to the wound tissues. These data support the hypotheses that insulin is a necessary component for an adequate wound healing response. In addition to a role in glucose transport and metabolism, insulin may also promote cellular growth.
Brief, Irregular Oscillations of Basal Plasma Insulin and Glucose Concentrations in Diabetic Man
Authors: Lang D A , Matthews D R , Burnett M , Turner R C
Published: September 2013

The basal plasma insulin and glucose concentrations of 12 diet-treated maturity-onset diabetics were measured at minute intervals for 2 h. Brief, irregular oscillations (mean period 8.8 min) in plasma insulin were superimposed on longer term fluctuations (> 30 min). Time series analysis demonstrated a synchronous plasma glucose oscillation (mean amplitude 0.03 mmol/L) associated with short insulin cycles. The glucose changes seen in diabetic subjects were similar to the short plasma insulin cycles (< 10 min) observed in normal subjects. In contrast, the longer plasma insulin cycles (> 10 min) of normal subjects were associated with a plasma glucose oscillation that rose before the end of the cycle. The demonstration of insulin oscillations independent of preceding plasma glucose changes in both normal and diabetic subjects suggests a pancreatic oscillating mechanism or “pacemaker.” The associated glucose changes may reflect the entrainment, by the insulin cycles, of glucose production or utilization.
Dual Effects of Veratridine on Glucagon and Insulin Secretion: Dependence upon Extracellular and Intracellular Calcium
Authors: Kawazu S , Ikeuchi M , Kikuchi M , Kanazawa Y , Fujimoto W Y , Kosaka K
Published: September 2013

The stimulatory effect of the sodium ionophore, veratridine (10, 25, and 50 μM), on glucagon and insulin secretion was investigated using monolayer cultures of newborn rat pancreas. The results suggest that intracellular accumulation of sodium modulates hormone secretion from both alpha- and beta-cells. The action of veratridine is dependent, at least in part, on the extracellular calcium, as its effect was attenuated or lost when extracellular calcium was deleted. Its action was also dependent on intracellular calcium since preincubation of cells in low, normal, or high calcium to diminish, maintain, or increase intracellular calcium, followed by incubation with veratridine in the absence of calcium, altered the secretory responses of both glucagon and insulin. Ouabain (0.5 mM) stimulated glucagon and insulin secretion, although its effect was less than that of veratridine (50 μM). These results suggest that a common releasing mechanism, dependent on extra- and intracellular calcium, is involved in both endocrine cells.
Effect of Genetic Obesity in Mice on the Induction of Diabetes by Encephalomyocarditis Virus
Authors: D'andrea B J , Wilson G L , Craighead J E
Published: September 2013

The “M” variant of the encephalomyocarditis (EMC) virus causes a diabetes-like disease in some, but not all, strains of mice. The genetic basis for either resistance or susceptibility to the diabetogenic effect of the virus is not known. After infection with EMC, C57BL/6 mice seldom develop hyperglycemia and the insular lesions are subtle. To explore the possible effects of metabolic influences on the viral susceptibility of the islets, we studied C57BL/6 mice that were carriers of the ob gene. After virus inoculation, obese homozygous C57BL/6-ob/ob mice consistently developed hyperglycemia during the acute stages of infection, whereas nonobese littermates did not. Infection induced more severe lesions in the pancreatic islets of obese mice than in islets of the lean littermates. These studies suggest that the functional activity of the beta-cells influences the severity of the viral injury to the beta-cell, and the consequent occurrence of diabetes.
Effects of Plasma Glucose Concentration on Glucose Utilization and Glucose Clearance in Normal Man
Authors: Verdonk Carlos A , Rizza Robert A , Gerich John E
Published: September 2013

Glucose clearance (glucose utilization ÷ plasma glucose) is commonly used to assess glucose utilization under conditions in which plasma glucose concentrations vary. The validity of this practice requires that glucose clearance itself be independent of plasma glucose concentration. The present studies were, therefore, undertaken to determine the relationship between glucose clearance and plasma glucose concentration in man. Using the glucose clamp technique, rates of glucose utilization (measured isotopically with 3-3H-glucose) and glucose clearance were determined in 5 normal volunteers at steady-state plasma glucose concentrations of approximately 60, 95,130, and 165 mg/dl, while plasma insulin concentrations were maintained constant (∼18 μU/ml) by infusion of insulin and somatostatin. Despite virtually identical 0.4 mg · kg−1 · min−1 increments in glucose utilization for each 35-mg/dl increment in plasma glucose, glucose clearance decreased as a function of plasma glucose concentration (r = − 0.85, P < 0.001). These results indicate that glucose clearance is not independent of changes in plasma glucose concentration and, thus, use of glucose clearance to evaluate glucose utilization at differing plasma glucose concentration is not valid. Whether this conclusion also applies to similar use of clearance for other substrates remains to be determined.
Glucose and Acetylcholine Have Different Effects on the Plateau Pacemaker of Pancreatic Islet Cells
Authors: Cook Daniel L , Crill Wayne E , Porte Daniel
Published: September 2013

Pancreatic islet cell membrane electrical activity has been studied with intracellular microelectrodes in perifused, isolated mouse islets of Langerhans. The doseresponse effects of glucose and of acetylcholine on the pattern of electrical activity are compared and are shown to be qualitatively different. Electrical activity in the presence of glucose consists of periodic alterations between a polarized silent phase potential and depolarized plateau phase with superimposed rapid spiking activity. Increasing glucose concentration prolongs the plateau phase, at the expense of the silent phase, and thus increases the plateau fraction (the fraction of time in each electrical cycle spent in the plateau phase). By contrast, graded doses of acetylcholine, in the presence of stimulatory levels of glucose, had no effect on plateau fraction. Increasing glucose concentration also slightly reduced the frequency of plateaus, whereas increasing acetylcholine markedly increased plateau frequency. Furthermore, changes of glucose concentration had no effect on the potential levels during the plateau and silent phases, while addition of acetylcholine depolarized the silent phase until, at high concentrations of acetylcholine, the combination of increased plateau frequency and silent phase depolarization produced continuous spiking. Addition of acetylcholine to a slightly substimulatory level of glucose depolarized the membrane without, however, inducing periodic spiking activity. The results suggest that the effects of acetylcholine and glucose are due to different effects on the plateau pacemaker system involved in the regulation Of insulin release.
Intestinal Sugar Transport in Experimental Diabetes
Authors: Csáky T Z , Fischer E
Published: September 2013

The increased sugar transport was examined in the isolated small intestine of streptozotocin-diabetic rats. In the small intestine of these animals, the rate of glucose absorption in vivo is slightly increased, but not that of galactose of 3-O-MG (3-O-Methylglucose); however, in the isolated small intestine, the mucosal-toserosal but not the serosal-to-mucosal flux of glucose, galactose, and 3-O-MG is increased. The enhanced sugar transport is due neither to the direct toxic effect of streptozotocin nor to a lack of circulating insulin. It is not the result of an increased intraepithelial sugar metabolism. Hyperglycemia, produced by i.v. glucose infusion, generates the same increase of the intestinal sugar transport as experimental diabetes but the high blood sugar has to be maintained for 4 h before the intestinal effect appears. Hyperglycemia and hypergalactosemia enhance the intestinal transport of glucose, galactose, and 3-O-MG, but not that of fructose; the transport of the latter is increased by hyperfructosemia. The enhanced intestinal sugar transport produced by high blood sugar is inhibited by phloretin but not by phlorizin and is completely eliminated in cycloheximide-treated animals. It is proposed that sustained high blood sugar induces the synthesis of new carrier sites which are most likely located in the basolateral membrane.
Islet Secretion in a New Experimental Model for Non-insulin-dependent Diabetes
Authors: Weir G C , Clore E T , Zmachinski C J , Bonner-Weir S
Published: September 2013

An animal model of diabetes mellitus has been developed in which neonatal rats are injected with streptozotocin at 2 days of age. After transient hyperglycemia followed by near normal glycemia, these animals develop nonketotic diabetes at about 6 wk of age that does not require insulin treatment. Secretion from the endocrine pancreas of 6–15-wk-old rats was evaluated with the isolated, perfused pancreas technique.

Insulin secretion responded very poorly to high perfusate glucose concentrations, but in the presence of theophylline this meager response was enhanced. In contrast, arginine elicited an insulin response comparable to that of the control rats. Isoproterenol stimulated insulin secretion more in the diabetic model than in the controls, and tolbutamide failed to evoke insulin secretion. Glucagon secretion in response to arginine and isoproterenol was similar in both groups, but was suppressed less efficiently by glucose in the model than in controls. Evidence for enhanced basal secretion of somatostatin was also found. Thus, these hyperglycemic rats have a selective defect in glucosestimulated insulin secretion with preservation of responses to other agents. In addition, abnormalities in the secretion of glucagon and somatostatin have been found.
Cardiac Arrhythmias During Epinephrine-Propranolol Infusions for Measurement of In Vivo Insulin Resistance
Authors: Lampman Richard M , Santinga John T , Bassett David R , Savage Peter J
Published: September 2013

Sixty-eight determinations of in vivo insulin resistance were conducted in 35 males (aged 29-63 yr) by measurement of steady-state plasma glucose levels during a combined intravenous infusion of propranolol, epinephrine, glucose, and insulin. Subjects were mildly diabetic and/or hyperlipidemic. All were asymptomatic, denied taking medication, and had no history of cardiac disease. All had normal resting electrocardiograms. During the infusion, mean increases in systolic and diastolic blood pressure were 27 ± 12.2 (X¯ ± SD) and 14 ± 5.7 mm Hg, respectively;, mean reduction in heart rate was 19 ± 6.1 beats/min. Six out of the 35 subjects developed cardiac arrhythmias during the infusion test. Maximal exercise treadmill tests failed to predict all subjects who subsequently developed arrhythmias during the infusion test. These results suggest that this infusion test should be performed under continuous cardiac monitoring and promptly terminated if major arrhythmias develop.
Hormonal, Metabolic, and Cardiovascular Responses to Hypoglycemia in Diabetic Autonomic Neuropathy
Authors: Hilsted J , Madsbad S , Krarup T , Sestoft L , Christensen N J , Tronier B , Galbo H
Published: September 2013

Hormonal, metabolic, and cardiovascular responses to insulin-induced hypoglycemia were investigated in 10 juvenile-onset diabetics who showed signs of autonomic neuropathy, in 8 control patients of similar age and duration of diabetes without neuropathy, and in 6 healthy subjects. In an attempt to normalize intermediary metabolism, the diabetics were treated with soluble insulin only (given subcutaneously and intravenously) for 48 h preceding the study.

Plasma epinephrine concentrations were significantly lower in patients with autonomic neuropathy before the experiment as well as 15 min after serum glucose nadir compared with diabetics without neuropathy (P < 0.05), indicating impaired sympathoadrenal activity. Plasma norepinephrine responses did not differ significantly. No significant increase was found in glucagon concentrations in patients with autonomic neuropathy, whereas a small increment was found in diabetics without neuropathy. Growth hormone and cortisol responses were similar in the two patient groups, and serum free insulin concentrations were also similar. In spite of blunted responses of glucagon and of epinephrine in the patients with autonomic neuropathy, serum glucose responses were similar to those of the diabetics without autonomic neuropathy. Furthermore, rate of lipolysis, as judged from FFA and glycerol concentrations, as well as systolic blood pressure increments were significantly greater (P < 0.05) in patients with autonomic neuropathy than in diabetics without neuropathy.

In conclusion, during insulin-induced hypoglycemia, patients with autonomic neuropathy had impaired activation of the adrenal medulla, probably due to sympathetic neuropathy. Furthermore, they had no increase in glucagon concentrations. Compared with noneuro-pathic diabetics, serum glucose recovery was unaffected and lipolytic responses and blood pressure increments were exaggerated, suggesting increased sensitivity of hepatic glycogenolysis, adipose tissue lipolysis, and the cardiovascular system toward the action of catecholamines in diabetics with autonomic neuropathy.
Correlation of Urinary Excretion of C-Peptide with the Integrated Concentration and Secretion Rate of Insulin
Authors: Meistas Mary T , Zadik Zvi , Margolis Simeon , Avinoam Kowarski A
Published: September 2013

The secretion rate of insulin (SR-I) of 50 normal subjects was calculated from the 24-h integrated concentration of insulin (IC-I), the peripheral metabolic clearance of insulin (pMCR-l), and the mean fractional hepatic insulin extraction (fhMCR-l) that was derived from our data. fhMCR-l was determined as the difference in the molar secretory rate of C-peptide (SR-C) and the molar peripheral clearance of insulin (pMCRI × IC-I) divided by SR-C. The IC-I in our 50 subjects was 1.19 ± 0.38 ng/ml and the IC-C was 2.93 ± 0.58 ng/ml. Based on these data, the fhMCR-l was 0.40 and the SR-I was estimated to be 54.8 ± 18.0 U/24 h.

The 24-h urinary C-peptide excretion (U-C), 44.9 ± 20.4 μg/24 h, had a statistically significant correlation with SR-I (r = 0.838, P < 0.0001), while the IC-I correlated significantly with the 24-h urinary C-peptide/g of creatinine (r = 0.823, P < 0.0001). The U-C may thus serve as a practical method for estimating the SR-I.
Abnormalities in the Biosynthesis of Cartilage and Bone Proteoglycans in Experimental Diabetes
Authors: Weiss Roy E , Gorn Alan H , Nimni Marcel E
Published: September 2013

Proteoglycans synthesized in developing cartilage and bone were investigated in control and streptozotocininduced (65 mg/kg, i.v.) diabetic rats. Ten days after streptozotocin injection, animals were implanted subcutaneously with demineralized bone matrix particles. This system induces formation of cartilage and bone on days 7 and 14, respectively. Two hours before they were killed, animals were injected with 35SO4 and the labeled proteoglycans were extracted from the explants and metaphyses by either a direct associative extraction (0.5 M GuCl2) or a direct dissociative extraction (4.0 M GuCl2). These procedures extract 80–90% of the total counts incorporated. To characterize the proteoglycans, extracts were subjected to cesium chloride density gradient centrifugation and molecular sieve chromatography. These data showed that (1) there is less proteoglycan made in diabetic bone; (2) the proteoglycan aggregate is of a smaller molecular weight in bone than in cartilage; (3) 10% of the proteoglycan synthesized in diabetic bone was in the form of aggregates compared with 48% of the control bone; (4) aggregates did form in the diabetic cartilage, and their molecular weight was smaller than in normal cartilage. This investigation shows that proteoglycans, structurally important macromolecules of cartilage and bone, are altered in experimental diabetes. This metabolic abnormality may be an important factor contributing to decreased bone formation observed in diabetes.
Waveform Requirements for Metabolic Normalization With Continuous Intravenous Insulin Delivery in Man
Authors: Perlman Kusiel , Ehrlich Robert M , Filler Robert M , Albisser A Michael
Published: September 2013

Devices and methods for long-term intravenous (i.v.) insulin infusion in ambulatory patients have recently been developed. However, to date optimal waveforms for open-loop insulin administration in severely insulin deficient patients have not been defined.

We studied 7 nonobese uncomplicated type 1 diabetics aged 16.5 ± 0.2 yr who received insulin continuously for 14–23 days by central venous infusion. A pattern of i.v. insulin administration was developed and eventually refined to include a constant basal infusion rate augmented at meal time by a series of 3 pulses. The first pulse lasted 10–15 min with an infusion rate 1.5–2 times the basal rate. The second pulse was 60–100 min in duration with a rate 4–6 times the basal infusion rate. The third pulse lasted 40–100 min with an infusion rate 1.5–3 times the basal rate. Accompanying the evolution of this waveform, the mean fasting plasma glucose fell from 262 ± 40 mg/dl on conventional therapy to 92 ± 9 mg/dl during infusion with normal meal excusions (mean a.c. glucose 80 ± 3 mg/dl with a rise of 35 ± 3 mg/dl at 41 ± 3 min). Mean urinary glucose excretion decreased from 55 before to 1.9 g/day during the infusion period. Fasting serum cholesterol and triglycerides dropped from 220 ± 28 and 281 ± 94 to 138 ± 13 and 115 ± 24 mg/dl, respectively.Mean HbA, declined from 14.8% before to 10.7% at the conclusion of the infusion period. All indices of control showed improvement significant at P < 0.05. There were no catheter-related complications and the system was well accepted by all subjects.

These studies confirm that continuous central venous insulin infusion with a relatively simple waveform is feasible for the prolonged normalization of glycemia and other indices of metabolic control in ambulatory adolescent diabetics.
The Diabetogenic Effects of Streptozotocin in Mice are Prolonged and Inversely Related to Age
Authors: Riley William J , McConnell Thomas J , McLaughlin Judith V , Taylor G
Published: September 2013

Single ‘subdiabetogenic’ doses of streptozotocin (SZ), when given to young male CD-1 mice, produced a delayed onset of hyperglycemia dependent on the dose of SZ and on the age of the mice. The effect was markedly reduced or absent in older mice given the same dose of SZ per kg of body Weight. Histologic examination of the pancreas of these animals revealed that SZ induced greater damage to the islets of the young mice compared with older mice. In addition to the characteristic findings of a decrease in insulincontaining cells and an increase in glucagon- and pancreatic polypeptide-containing cells there was evidence of new islet formation.

Delayed-onset hyperglycemia was also induced in young inbred DBA/2J, C57BL/KsJ, and SWR/J mice with single SZ doses, as well as with alloxan in young CD-1 mice, indicating that the effect was not specific for CD-1 mice nor for SZ as the agent inducing β-cell injury.

The induction of β-cell autoimmunity did not appear to be important in the delayed diabetogenic effect of SZ, since insulitis was rare and followed the onset of hyperglycemia when seen, and islet cell autoantibodies were not found. Rather, SZ induced more β-cell destruction in young animals than in older mice, and the continued somatic growth of the former suggests that the delayed hyperglycemia was due to an outgrowing of a reduced insulin supply. That mild to severe diabetes could be induced by the same dose of SZ/kg, depending only on the age of mice when SZ was given, may have implications for understanding the apparent heterogeneity of human diabetes mellitus.
Radioimmunoassay of Human Plasma Somatostatin
Authors: Mackes K , Itoh M , Greene K , Gerich J
Published: September 2013

Human plasma somatostatin-like immunoreactivity (SLI) is heterogeneous. Moreover, human plasma contains a somatostatin-binding protein, enzymes that degrade the peptide, and other poorly characterized substances that interfere in radioimmunoassays of the peptide. Previously described extraction methods only partially circumvent these problems and generally result in less than adequate recovery. The present studies were therefore undertaken to determine whether gel filtration of plasma could be used to avoid these difficulties and provide a means for radioimmunoassay of plasma somatostatin in man. Gel filtration (Sephadex G25) of human plasma and subsequent radioimmunoassay of column eluates using five different antisera uniformly demonstrated two fractions of SLI in plasma. One fraction (peak I) eluted in the void volume and had an apparent molecular weight in excess of 150,000 daltons; this material comprised most of the plasma SLI, did not dilute in parallel with synthetic somatostatin, and decreased immunoprecipitability of both N-tyrosine- and tyrosine-11-125I somatostatin. The second fraction (peak II) coeluted with synthetic somatostatin (apparent mol. wt. 1600 daltons), diluted in parallel with synthetic somatostatin, and did not appreciably degrade either 125I-tyrosylated analogue. Synthetic somatostatin added to plasma was recovered nearly completely (95 ± 3%) in peak II SLI. Infused synthetic somatostatin increased peak II SLI but did not alter peak I SLI. These results demonstrate that gel chromatography of human plasma before assay can be used to circumvent problems of immunoheterogeneity, 0degradation, and nonspecific interference while providing adequate recovery. With this method, mean plasma somatostatin concentrations (peak II SLI) in postabsorptive normal volunteers ranged from approximately 40 to 100 pg/ml, depending on the antibody system used. These concentrations (3–6 × 10−11 M) are of similar magnitude to thosereported to affect reputed target tissues of somatostatin in vitro and are thus consistent with a possible hormonal function for the peptide.
Insulin Release: Demonstration of a Priming Effect of 3-Isobutyl-1-Methyl-Xanthine (IBMX) on Islets of Langerhans
Authors: Wiedenkeller Dayna E , Sharp Geoffrey W G
Published: September 2013

Exposure of isolated rat pancreatic islets to 1 mM 3- isobutyl-1-methyl-xanthine (IBMX) resulted in a 5.7-fold increase in the rate of insulin release. After a 30-min rest period under basal conditions, reexposure of the islets to 1 mM IBMX resulted in an enhanced rate of release when compared with either a timed control—islets simultaneously exposed to IBMX for the first time—or with the first priming response to IBMX. The possibility of a continuous priming effect was suggested by the gradually rising rate of insulin release during exposure to IBMX. It is concluded that islets have a memory for IBMX exposure that results in increased responsiveness to subsequent stimulation by IBMX.