bluuebunny/crossref_metadata_2025 huggingface dataset:
Important Role of Adrenergic Mechanisms in Acute Glucose Counterregulation Following Insulin-induced Hypoglycemia in Type I Diabetes: Evidence for an Effect Mediated by Beta-Adrenoreceptors
Authors: Bolli Geremia , Feo Pierpaolo De , Compagnucci Pietro , Cartechini Maria G , Angeletti Gabriella , Santeusanio Fausto , Brunetti Paolo
Published: September 2013

During hypoglycemia induced by an i.v. insulin infusion for 60 min, rates of plasma glucose (PG) decrease and recovery, PG nadir, and plasma counter-regulatory hormone and free fatty acid responses were studied in eight type I uncomplicated diabetic subjects and eight nondiabetic subjects. Each subject was tested three times at two different rates of insulin infusion (25 and 32 mU/m2/min): (1) during infusion of saline, (2) during infusion of phentolamine + propranolol (combined alpha, beta-blockade), and (3) during infusion of propranolol alone (isolated beta-blockade) for 150 min. At the time of the studies, the diabetic subjects had been made euglycemic by an overnight i.v. insulin infusion. During infusion of insulin (25 mU/m2/min) and saline, the rates of PG decrease and recovery were slower (P < 0.01) and PG nadir was delayed in the diabetic subjects. Moreover, their plasma glucagon response was blunted while plasma epinephrine, norepinephrine, growth hormone, and cortisol responses were similar in both groups. Infusion of insulin at 32 mU/m2/min caused larger decreases in PG than had been observed when insulin was infused at 25 mU/m2/min. Plasma glucagon responses increased in the nondiabetic subjects (P < 0.05) but not in the diabetic subjects. However, in the diabetic subjects, plasma epinephrine increased more than in the nondiabetic subjects (P < 0.05). There was an inverse correlation between the individual plasma epinephrine responses and the plasma glucagon responses in the diabetic subjects (r = −0.72) but not in the nondiabetic subjects. Alpha, beta-adrenergic blockade decreased the plasma glucose nadir and impaired the rate at which normoglycemia was restored in the diabetic subjects (P < 0.005 vs. saline) but not in the nondiabetic subjects. Plasma catecholamine and growth hormone responses were increased and plasma FFA recovery was suppressed in both groups (P < 0.05 vs. saline), while the cortisol responses were unaltered. During isolated beta-adrenergic blockade, changes in plasma glucose, counterregulatory hormones and FFA were essentially identical to those observed during combined alpha, beta-adrenergic blockade in both groups except that the augmented plasma norepinephrine responses were no longer apparent. Conclusions although epinephrine is not essential for prompt restoration of normoglycemia in normal man following insulin-induced hypoglycemia, it plays a major role in glucose counterregulation in diabetics who have an impaired glucagon secretion in response to hypoglycemia. These counterregulatory effects of epinephrine are mediated by beta-adrenoreceptors.
Cell-Free Synthesis of Rat Insulin-like Growth Factor II
Authors: Acquaviva Angela Maria , Bruni Carmelo Bruno , Nissley S Peter , Rechler Matthew M
Published: September 2013

Total RNA extracted from a rat liver cell line (BRL 3A) that synthesizes rat insulin-like growth factor II (IGF-II) was translated in a reticulocyte lysate cell-free system. Incubation of the translation products with antisera to mature rat IGF-II (Mr 8700) selectively immunoprecipitated a Mr 21,600 protein. We propose that this protein represents pre-pro-IGF-II.
Direct Demonstration of Insulin Receptor Internalization: A Quantitative Electron Microscopic Study of Covalently Bound 125I-photoreactive Insulin Incubated with Isolated Hepatocytes
Authors: Gorden Phillip , Carpentier Jean-Louis , Moule Margaret L , Yip Cecil C , Orci Lelio
Published: September 2013

When 125I-insulin is incubated with isolated rodent hepatocytes at 37°C, the ligand initially binds to the plasma membrane of the cell and is subsequently internalized by adsorptive endocytosis. To confirm directly that the insulin receptor is internalized with the ligand, we covalently linked photoreactive 125I-NΣB29 (azidobenzoyl) insulin to its specific hepatocyte receptor and followed its fate by quantitative electron microscopic autoradiography. We found that the covalently linked photoreactive insulin is internalized by the cell in fashion analogous to the internalization of ordinary 125I-insulin, indicating that, at least under these conditions, the insulin receptor is internalized with the ligand.
Axonal Dystrophy in Experimental Diabetic Autonomic Neuropathy
Authors: Schmidt Robert E , Scharp David W
Published: September 2013

Autonomic neuropathy involving the alimentary tract of several strains of inbred rats with chronic streptozotocin-induced diabetes has been characterized using ultra structural methods. Markedly enlarged unmyelinated axons in the Heal mesentery of diabetic rats contain a variety of normal and unusual subcellular organelles similar to those described in experimental and clinical axonal dystrophies, these axonal alterations were seen after 6, 9, and 12 mo of diabetes, apparently increasing in frequency with time; lesions were absent, however, after only 3½ mo of diabetes. An apparent proximo-distal gradient in the frequency of unmyelinated axonal lesions in this system suggests experimental diabetic autonomic neuropathy may represent an example of distal axonopathy. In addition, we have demonstrated an association of dystrophic axons with regenerative structures, including growth cones and clusters of filopodia.
Importance of Glucose Control for the Recovery from Hypoglycemia in Insulin-dependent Diabetics
Authors: Lager Ibe , Blohmé Göran , Schenck Henning V , Smith Ulf
Published: September 2013

To evaluate whether the delayed glucose compensation after hypoglycemia in insulin-dependent diabetics was associated with their elevated blood glucose levels, five diabetic patients were studied before and after a period of intensified metabolic control. The glucose recovery rate was found to be improved after better diabetic control. This influence seems to be better reflected by the mean diurnal level rather than the glucose level immediately before hypoglycemia. The improvement occurred despite the same or lower levels of the important glucocompensatory hormones. These results show the importance of antecedent metabolic control for glucose compensation after hypoglycemia.
Proximal Motor Neuropathy in the BB-Wistar Rat
Authors: Sima Anders A F , Thibert Pierre
Published: September 2013

Proximal motor neuropathy is a well-recognized neuropathic complication in human diabetes mellitus, due to microvasculopathic changes. Spontaneously diabetic BB-Wistar rats maintained at a moderate severity of diabetes developed structural proximal motor neuropathy after long-standing diabetes. This was caused by multiple infarcts in the spinal ventral roots. Endoneurial Vessels showed occlusions by platelet aggregates and unstriated fibrin, indicative of a hypercoagulability.
Insulin Resistance is a Prominent Feature of Insulin-dependent Diabetes
Authors: DeFronzo Ralph A , Hendler Rosa , Simonson Donald
Published: September 2013

Tissue sensitivity to insulin was examined in 36 control subjects and 19 insulin-dependent diabetics with diabetes of long-standing duration (mean = 10 ± 3 yr) employing the insulin clamp technique (Δ plasma insulin concentration ∼100 βU/ml). Eleven of the diabetics (group I) were studied at their fasting hyperglycemic level (173 mg/dl); the remaining 8 diabetics (group II) were studied after lowering their plasma glucose concentration to euglycemic levels (90 mg/dl). Despite plasma glucose levels that were almost twice as great in the diabetics (group 1,173 versus 91 mg/dl, P < 0.001), insulin-mediated glucose metabolism, 4.77 ± 0.18 mg/kg · min, was reduced by 32% versus controls, 7.03 ± 0.22 mg/kg · min (P < 0.01). When the control subjects were restudied at plasma glucose levels (166 ± 2 mg/dl) that were comparable to those of the diabetics, insulin-mediated glucose metabolism was 12.14 ± 0.96 mg/kg · min (P < 0.01). In diabetics studied at euglycemic levels (group II) insulin-mediated glucose metabolism, 3.39 ± 0.30 mg/kg · min, was reduced even further. The metabolic clearance rate in the 19 diabetics, 3.31 ± 0.23 mg/kg · min, was reduced by 58% compared with controls, 7.83 / 0.25 (P < 0.001). These results emphasize the severe degree of insulin resistance that exists in the insulin-dependent diabetics. Basal hepatic glucose production in the diabetic group, 2.96 ± 0.24 mg/kg · min, was 26% greater than in the controls, 2.35 ± 0.04 (P < 0.001). The fasting plasma glucose concentration displayed a strong positive correlation (r = 0.857, P < 0.001) with basal hepatic glucose production and was weakly and inversely correlated (r = −0.413, P = 0.07) with the basal glucose clearance. Following hyperinsulinemia, however, suppression of hepatic glucose production was ∼ 9 5% in both diabetics and controls, suggesting that peripheral tissues are primarily responsible for the observed impairment in insulin-mediated glucose uptake. The present results indicate that impaired insulin action is a common feature of insulin-dependent diabetics, despite daily insulin requirements (35 ± 2 U/day) that would not clinically characterize them as being insulin resistant.
Insulin Content of Fetal Mouse Pancreas in Organ Culture and After Transplantation
Authors: Hoffman L , Mandel T E , Carter W
Published: September 2013

Organ-cultured fetal mouse pancreas was transplanted into syngeneic diabetic mice and the insulin content of the graft measured. Insulin content of each 17-day-old uncultured fetal mouse pancreas was 90 ± 10 ng, rising to 457 ± 123 ng after 16 days in organ culture (P < 0.001); however, after 35 days in vitro, it decreased to 108 ± 59 ng. Diabetes was induced in mice with streptozotocin (STZ), and 3 wk later each animal was grafted under the kidney capsule with one syngeneic fetal pancreas cultured for 16 days. Total insulin content of fetal pancreata increased from 457 ± 123 ng on the day of transplantation to peak at 12,125 ± 3679 ng by 9 wk after grafting (P < 0.001), at which time insulin content of grafts was comparable to that extracted from normal adult mouse pancreas (8917 ± 436 ng). Random blood glucose in mice following STZ was 15.7 ± 0.9 mmol/L and declined to normal levels (5.6 ± 0.5 mmol/L) 6 wk after transplantation. Insulin content of the pancreas after STZ injection decreased from 8917 ± 436 ng to 906 ± 410 ng at 15 wk (P < 0.001) in diabetic mice that were not islet grafted. However, pancreatic insulin content of grafted mice was significantly greater than in ungrafted mice 15 wk after STZ (3168 ± 532 ng versus 906 ± 410 ng, P 0.01), which suggests that islet transplantation protects residual pancreatic function. It is concluded that fetal islets have a large capacity to produce and accumulate insulin in vitro and in vivo, and each grafted fetal pancreas may attain an insulin content equivalent to that of a normal adult pancreas. The potential of fetal islets to accumulate large insulin reserves may make possible the use of tissue from one donor to treat multiple recipients.
Glucose but not Arginine Prevents the Inhibitory Effect of Vincristine on Glucose-induced Insulin Release
Authors: Shah Jayendra H , Schickler Renee , Hurks Charles , Stevens Bernard
Published: September 2013

We have previously shown that in the intact rat: (1) the inhibition of glucose-induced insulin release caused by vincristine occurred in the presence or absence of morphologic disruption of the beta-cell microtubules; and (2) vincristine, however, failed to inhibit arginine-induced insulin release, even in the presence of a marked disruption of the beta-cell microtubules. The present study further evaluated the mechanism of inhibition of vincristine on glucose-induced insulin release in the intact rat. In the first series of studies, glucose (500 mg/kg) was infused over 1 min into fasting rats with indwelling vascular catheters. Five minutes later, vincristine (0.15 mg/kg i.v.) or vehicle (control) was injected. Sixty minutes after vincristine or vehicle treatment, insulin release in response to a 150-mg i.v. glucose pulse was examined. Serum insulin and glucose levels were similar at all time intervals in the vincristine-treated and the control rats. In the next series of studies, the experiments were repeated as above, except arginine (100 mg/kg), instead of glucose, was infused over 1 min before vincristine or vehicle treatment. In these studies, serum insulin in response to a glucose pulse was significantly inhibited in the vincristine-treated rats as compared with control rats. Therefore, in the intact rat, prior exposure to glucose but not arginine protected the beta-cell from the inhibitory effect of vincristine on glucose-induced insulin release. These findings, along with our previous observations, support the concept that arginine-induced insulin release is mediated via mechanisms other than those involved in glucose-induced insulin release and suggest that the in vivo effect of vincristine on glucose-induced insulin release is mediated via alteration of the beta-cell glucose receptors rather than microtubular structures.
Immunoreactive Neurotensin in the Pancreas of Genetically Obese and Diabetic Mice: A Longitudinal Study
Authors: Berelowitz Michael , Frohman Lawrence A
Published: September 2013

Immunoreactive neurotensin (IR-NT) content in 2 N acetic acid extracts of pancreas was measured in genetically diabetic (C57BL/KsJ db/db and ob/ob) and obese (C57BL/6J ob/ob and db/db) mice and normal littermate controls from 5 to 24 wk of age to determine the relationship of any changes to the development of metabolic abnormalities. Pancreatic IR-NT in obese mice showed no consistent change compared with lean littermate controls. In contrast, diabetic mice demonstrated an increase in pancreatic IR-NT that occurred at 6–8 wk of age, and maximal about the time of islet B-cell failure (8–10 wk), and persisted over the study period. Pancreatic IR-NT eluted in two peaks on reverse phase high-pressure liquid chromatography, one of which exhibited a retention time similar to that of synthetic NT. These findings suggest that pancreatic IR-NT concentration is regulated by insulin, with elevated levels occurring in association with insulin deficiency and its metabolic consequences but not with insulin resistance. Taken together with the previous demonstration that NT influences pancreatic islet hormone secretion, the present findings support a possible role of endogenous NT in islet hormone regulation.
Effect of MtTW15 Mammosomatotropic Tumors on Pancreatic Islet Hormones
Authors: Parsons Jonathan A , Hartfel Margaret A , Hegre Orion D , McEvoy Robert C
Published: September 2013

The effects of hypersecretion of growth hormone and prolactin on islet endocrine cells have been studied by radioimmunoassays, immunocytochemistry, and morphometry in randomized samples of pancreata from MtTW15 mammosomatotropic tumor-bearing and control rats. The randomized sampling procedure, validated by immunoassays, allowed evaluation of both hormone content (immunoassay) and endocrine cell population (immunocytochemistry) on samples derived from the same origin. Hyperinsulinemia (2×) and non-fasting hypoglycemia in 10-wk-tumor rats were normalized 3 wk after tumor removal. Pancreatic weight was doubled, but proportional to body weight increases. Islet/pancreas ratio was constant (1.29 ± 0.05%) and the same in tumor, tumor-removed, and control animals, but average islet dimensions were increased by 30% and average area doubled in tumor animals. Frequency analysis showed fewer small (< 70 μm) and more large (> 140 μm) islets in tumor animals, but no change in average islet shape shown by average axis ratios of 1.4 in all groups. Pancreatic content of insulin and glucagon was doubled, while that of somatostatin was constant. These changes were not completely reversed in tumor-removed animals. Similarly, a significant doubling in islet-derived mass was mainly due to a doubling of the B-cell mass as the average proportion of endocrine cells per islet shifted from 66%, 26%, and 18% to 81%, 18%, and 3% for B-, A-, and D-cells of control and tumor-bearing rats, respectively. Immunocytochemically detectable insulin was found in duct cells of tumor animals, but not controls. Whether such cells represent a functional reserve remains to be determined.
Monoclonal Antibodies Defined Abnormalities of T-Lymphocytes in Type I (Insulin-dependent) Diabetes
Authors: Pozzilli P , Zuccarini O , Iavicoli M , Andreani D , Sensi M , Spencer K M , Bottazzo G F , Beverley P C L , Kyner J L , Cudworth A G
Published: September 2013

Peripheral T-lymphocytes subsets have been investigated in 36 patients with type I (insulin-dependent) diabetes of varying duration, 18 patients with type II (non-insulin-dependent) diabetes, and in 23 healthy subjects, using six different monoclonal antibodies. At the time of diagnosis of type I diabetes, there was evidence of an increase in cytotoxic T-lymphocytes, a decrease in suppressor T-lymphocytes, but a normal proportion of helper/inducer T-lymphocytes. In six of seven newly diagnosed cases studied, there was evidence of an increased number of activated T cells. An increase in activated T-cells was also found in 5 of 10 genetically susceptible islet cell antibody positive unaffected siblings in type I diabetic probands. In type I diabetes of long standing, the total T-cell population was decreased, largely due to a marked decrease in helper/inducer T-lymphocytes. Type II diabetic patients showed no abnormalities in T-lymphocyte subsets, making it unlikely that hyperglycemia was responsible for the changes observed. These results suggest that an imbalance of T-lymphocyte regulation is an important feature of type I diabetes and lend support for an immunologic role in its early pathogenesis.
Effects of Body Composition on Insulin Sensitivity
Authors: Yki-Järvinen Hannele , Koivisto Veikko A
Published: September 2013

We studied the effects of body composition and maximal aerobic power on insulin sensitivity in 23 normal-weight, healthy male subjects. Eight were weight lifters, eight were long-distance runners, and seven were untrained controls. In each subject, the percentage of body weight (BW) made up of muscle and fat tissue (% muscle and % fat, respectively), the maximal aerobic power (O2max), and the tissue sensitivity to insulin were measured. The weight lifters were characterized by 35% higher % muscle as compared with the runners or controls (P < 0.01). O2max in the runners was 30–40% higher than in the weight lifters or controls (P < 0.001). During the euglycemic clamp studies, similar steady-state plasma glucose and insulin levels were achieved in each group. When calculated per total BW, the rate of glucose metabolism (M) was virtually identical in the weight lifters (10.26 ± 1.02 mg/kg BW/min) and the runners (10.03 ± 0.86 mg/kg BW/min), and 40–45% higher than in the controls (7.10 ± 0.75 mg/kg BW/min, P < 0.05). When calculated per muscle mass (Mm), only the runners had a higher than normal rate of glucose metabolism (P < 0.02). M was directly proportional to % muscle (r = 0.54, P < 0.01) and inversely related to % fat (r = −0.72, P < 0.001). The multiple linear regression analysis revealed a highly significant multivariate correlation between M and the combined effect of % muscle, % fat, and VO2max (r = 0.78, P < 0.0005). In addition, a regression equation for the predicted M was obtained as follows: M (mg/kg BW/min) = 0.697 + 0.155 % muscle − 0.312 % fat + 0.065 VO2max (ml/kg/min).

In conclusion, first, body sensitivity to insulin is directly related to muscle mass and inversely proportional to adiposity. Second, it may be possible in healthy man to predict the rate of glucose metabolism when body composition and O2max are known.
Increased Efficiency of Weight Gain and Altered Cellularity of Brown Adipose Tissue in Rats with Impaired Glucose Tolerance During Diet-induced Overfeeding
Authors: Cunningham John , Calles Jorge , Eisikowitz Leon , Zawalich Walter , Felig Philip
Published: September 2013

We examined the relationship among glucose tolerance, efficiency of weight gain, and cellularity of brown adipose tissue (BAT) in rats (initial weight: 362 ± 1 g) made hyperphagic and obese by feeding on a highly palatable “cafeteria” (CAF) diet for 4–8 wk. As compared with chow-fed controls, CAF feeding resulted in a 45–60% increase in caloric intake (P < 0.01), a 40–50% increase in weight gain (P < 0.01), and hyperinsulinemia. Glucose disposal rate (K) on intravenous glucose tolerance test (IVGTT) was ≥ 1.4% in all chow-fed rats, but fell to ≤ 1.3 in 10 of 23 CAF-fed rats. As compared with the chow-fed controls, rats with normal glucose tolerance demonstrated a 12% decline in efficiency of weight gain (g/100 kcal of food consumed) in response to CAF feeding (P < 0.05). In marked contrast, in rats with impaired glucose tolerance, efficiency of weight gain failed to decline in response to overfeeding and was 18% higher than in the overfed group with normal glucose tolerance (P < 0.01). Although CAF feeding increased the mass of interscapular BAT by 110–130% in rats with normal as well as impaired glucose tolerance, DNA content of BAT rose only in the normal-K CAF-fed rats (0.19 ± 0.01 mg DNA/100 mg versus 0.12 ± 0.02 in chow-fed controls and 0.12 ± 0.01 in low-K rats).

We conclude that (1) impaired glucose tolerance accompanying dietary-induced obesity is associated with an increase in efficiency of weight gain and (2) failure of BAT cellularity to increase may contribute to the increase in efficiency. These data suggest that the link between obesity and diabetes may be bidirectional: obesity increases the risk of diabetes while impaired glucose tolerance may accelerate the development of obesity by enhancing efficiency of weight gain.
Insulin Administered Intranasally as an Insulin-Bile Salt Aerosol: Effectiveness and Reproducibility in Normal and Diabetic Subjects
Authors: Moses Alan C , Gordon Gilad S , Carey Martin C , Flier Jeffrey S
Published: September 2013

Efficacy and reproducibility of insulin administered intranasally as an insulin-deoxycholate 1% (w/v) aerosol to normal and diabetic subjects were assessed by measurements of blood glucose and serum insulin levels. Following administration of 0.5 U insulin/kg with the unconjugated bile salt to fasting volunteers (N = 29), peak serum insulin levels of 103 ± 49 μM/ml above baseline were observed at 10 min. Blood glucose concentration began to fall by 10 min, reaching 54 ± 14% of control levels by 30 min, and returning to baseline by 60–80 min. Blood glucose response and peak serum insulin levels were reproducible when the same aerosol dose was repeatedly administered to the same subjects; however, intersubject variations were noted. By comparing serum insulin levels after i.v. and nasal routes of administration, nasal insulin absorption was approximately 10% as efficient as intravenous insulin. Dose response studies revealed that peak serum insulin concentrations were a linear function of the administered dose. In subjects with type I and type II diabetes mellitus, serum insulin levels increased in a manner similar to controls, and resulted in a prompt reduction of blood glucose concentration. However, in contrast to normal subjects, the duration of the glucose response was more prolonged, lasting as long as 5 h. Nasal administration of insulin as an aerosol with bile salts or bile salt analogs should be further evaluated as a possible nonparenteral approach to insulin therapy.
Anti-Islet Immunity and Thymic Dysfunction in the Mutant Diabetic C57BL/ KsJ db/db Mouse
Authors: Debray-Sachs Monique , Dardenne Mireille , Sai Pierre , Savino Wilson , Quiniou Marie-Christine , Boillot Dominique , Gepts Willy , Assan Roger
Published: September 2013

Anti-islet immune reactions were studied in vitro in genetically diabetic homozygote C57BL/KsJ db/db mice, using murine islet cells as a target. Spleen lymphocytes inhibited insulin secretion by the islet cells. This inhibition was abolished when T-cells were eliminated by treatment with anti-Thy 1.2 monoclonal antibody in the presence of complement. Anti-islet complement-dependent antibody (CDA) and antibody-dependent cell cytotoxicity (ADCC) were also found in the sera of these mice. This anti-islet immunity was detectable as early as the tenth day of life and lasted throughout the entire life span of the animals. A significant lymphopenia was detected in thymus and spleen cell populations. None of these anomalies was found in control heterozygote mice.

Thymic function was explored in the same mice by evaluating their serum thymic factor (FTS) levels using a rosette assay. The age-dependent decline of FTS levels was significantly accelerated in diabetic mice as compared with heterozygous littermates. Futhermore, FTS inhibitory immunoglobulins were detected in db/db mouse sera, which inactivated in vitro the biologic potency of synthetic FTS. Histologically, the thymus displayed an accelerated involution. It was shown by indirect immunofluorescence using anti-FTS monoclonal antibodies that the number of FTS+ cells was reduced in db/db mouse thymuses.

Histologie study of the islets of Langerhans showed early signs of β-cell hyperactivity and hypertrophy, followed by β-cell rarefaction and profound dislocation of islet architecture. Insulitis was not detected.
Effects of Maternal Diabetes on Early Embryogenesis: The Role of Insulin and Insulin Therapy
Authors: Sadler T W , Horton W E
Published: September 2013

Using the system of whole embryo culture the effects of insulin on early mouse embryogenesis were investigated. Three experimental approaches were employed in which (1) serum from diabetic rats receiving insulin therapy was used as culture medium; (2) insulin was added directly to serum collected from diabetic rats for use as culture medium; (3) insulin was added directly to medium (serum) collected from control rats. Mouse embryos were cultured in each of these media for 24 h and then evaluated for growth and malformations. The results demonstrated that insulin therapy was effective in reducing the incidence of malformations and growth retardation produced by serum from diabetic rats receiving no hormone supplement. However, addition of insulin directly to serum collected from diabetic rats was not effective in reducing the rate of abnormalities produced by this medium. Finally, addition of insulin at extremely high concentrations (10,000 μ/ml) produced no abnormal embryos. Thus, it appears that insulin therapy is successful in reducing malformation rates and that the hormone itself is not teratogenic in this system.
Vasoactive Intestinal Polypeptide-like Immunoreactive Nerves in Diabetic Penis: A Comparison Between Streptozotocin-treated Rats and Man
Authors: Crowe R , Lincoln J , Blacklay P F , Pryor J P , Lumley J S P , Burnstock G
Published: September 2013

Vasoactive intestinal polypeptide (VIP) has been demonstrated by immunofluorescence histochermistry in nerves in human and rat penile tissue. A reduction in VIP-like immunoreactivity in nerves was revealed in tissue from streptozotocin-diabetic rats and a human diabetic with impotence. These results suggest that an impairment in the VIP-ergic innervation in penile tissue may be an important factor in the development of impotence in diabetes. They also support the view that the streptozotocin-treated rat is a useful experimental model for diabetic autonomie neuropathy.
Polyol Pathway Activity and Myo-Inositol Metabolism: A Suggested Relationship in the Pathogenesis of Diabetic Neuropathy
Authors: Finegold David , Lattimer Sarah A , Nolle Sandra , Bernstein Marcy , Greene Douglas A
Published: September 2013

Two major metabolic perturbations, increased polyol (sorbitol) pathway activity and reduced tissue myo-inositol content, are induced in peripheral nerve by hyperglycemie. Although they are commonly invoked as alternative biochemical pathogenetic mechanisms for diabetic neuropathy, their possible interrelationship has never been adequately explored. Therefore, we studied the effect of polyol pathway blockade with sorbinil, a specific inhibitor of aldose reductase, on nerve myo-inositol content in acutely streptozotocin-diabetic rats. Sorbinil administration completely prevented the fall in nerve myo-inositol, thereby implicating increased polyol pathway activity as a likely factor in the fall in nerve myo-inositol content in experimental diabetes.
Impaired Glycogenic Substrate Activation of Glycogen Synthase Is Associated With Depressed Synthase Phosphatase Activity in Diabetic Rat Liver
Authors: Langdon David R , Curnow Randall T
Published: September 2013

Glucose and gluconeogenic substrates promote the activation of hepatic glycogen synthase in vivo and in vitro; activation occurs as inactive glycogen synthase D is dephosphorylated to active glycogen synthase I by glycogen synthase phosphatase. Impairments of glycogen accumulation and glycogen synthase activation in diabetes have been attributed to decreased glycogen synthase phosphatase activity. To determine the role of glycogen synthase phosphatases associated with cytosol and smooth endoplasmic reticulum in the impairment of glycogen synthase activation, livers of normal and streptozotocin-diabetic fed rats were sampled by freeze-clamping before and after perfusion with a mixture of 25 mM glucose, 10 mM glutamine, 4 mM lactate, and 1 mM pyruvate. Perfusion induced activation of glycogen synthase in normal rats, but activation was reduced in the diabetic rats in proportion to the severity of insulin deficiency (r = 0.72, P < 0.0001). There was also a close correlation between insulin levels and glycogen synthase phosphatase activities of both cytosol (r = 0.76, P < 0.0001) and SER (r = 0.71, P < 0.0001) fractions. In contrast, glycogen phosphorylase phosphatase activity and inactivation of glycogen phosphorylase during perfusion were normal in the diabetic livers. This is the first demonstration that glycogen synthase phosphatase activities in both soluble and SER fractions of liver cells are closely related to circulating insulin levels, and that the impairment of glycogen synthesis in diabetes may result from deficient glycogen synthase phosphatase activity in both cell compartments.
Peripheral Nerve Abnormalities in the Diabetic Mutant Mouse
Authors: Sharma A K , Thomas P K , Gabriel G , Stolinski C , Dockery P , Hollins G W
Published: September 2013

Observations were made on the genetically diabetic C57BL/KS (db/db) mouse. Morphometric observations were performed on the tibial nerve at 6, 9, and 15 mo and compared with those from nondiabetic (m/m) controls. Myelinated fiber size was less in the diabetic animals at all stages and affected cross-sectional axon area and myelin thickness equally. Unmyelinated axons were unaffected. The index of circularity of myelinated axons did not differ between diabetic and control animals. No definite absolute reduction in fiber size occurred and degenerative changes, which were slight, were equally frequent in the diabetic and control nerves. Axonal glycogenosomes, polyglucosan particles, and Schwann cell/axon networks, and Schwann cell Reich granules increased with age in both groups, but only glycogenosomes were consistently more numerous in the diabetic animals.

Counts of membrane associated particles in both P and E faces revealed that these were reduced in number in the diabetic animals in myelin and in the axolemma of unmyelinated axons, but not in the axolemma of myelinated fibers.

Growth in tibial length was also reduced in the diabetic animals and this suggested that the reduced fiber diameter probably represented a maturational deficit. The absence of a selective reduction in axonal size did not favor a primary axonopathy as the cause.
The Effect of Immunosuppression on Streptozotocin-induced Diabetes in C57BL/KsJ Mice
Authors: Leiter Edward H , Beamer W G , Shultz L D
Published: September 2013

The objective of this study was to determine whether mature thymic-derived T-lymphocytes were required for streptozotocin (SZ)-induced insulitis. C57BL/KsJ male mice were immunocrippled by thymectomy at 3 wk of age followed 1 wk later by lethal irradiation (1000 R) and hematopoietic reconstitution with syngeneic bone marrow (pretreated with anti-Thy 1.2 antiserum and complement to eliminate mature T-lymphocytes). As a control for the systemic effects of lethal irradiation itself, thymus-intact males were also irradiated and reconstituted with anti-Thy-1.2-treated marrow cells. This latter treatment resulted in a reconstitution of functional T-lymphocytes. Independent of the presence or absence of functional T-lymphocytes, irradiation extensively damaged the testes and produced at least a 50% reduction in plasma testosterone levels. In such effeminized males, the hyperglycemic response following 6 daily injections of SZ (35 mg/kg) was reduced in comparison to unirradiated males. Pancreatic insulin content was reduced 50% in both thymus-intact and thymectomized groups receiving lethal irradiation and SZ treatment; this correlated with histologic findings of small, beta-cell-depleted islets. Focal leukocytic infiltrates of the exocrine pancreas were induced by the irradiation. Streptozotocin-induced Insulitis was also observed regardless of the presence (in thymus-intact mice) or absence (in thymectomized mice) of phytohemagglutinin-responsive T-lymphocytes. Both groups exhibited intact B-lymphocyte function as measured by proliferative responsiveness to lipopolysaccharide. Severe immunosuppression of both T- and B-lymphocyte function was produced by subcutaneous injection of hydrocortisone into thymectomized mice 48 h prior to initiation of SZ treatments. This treatment prevented SZ-induced beta-cell necrosis and eliminated lymphocytic infiltrates in the endocrine and exocrine pancreas. We conclude that functional (mature) T-lymphocytes are not required to mediate the beta cytotoxicity of multiple low doses of SZ in inbred strains in which insulitis accompanies islet destruction. The ability of hydrocortisone to protect beta-cells from the direct cytotoxic action of SZ as well as to eliminate leukocytic infiltration in the pancreas would support the hypothesis that insulitis is a consequence of beta-cell destruction, in this model, rather than its cause.
Tubular Reabsorption Rates as Related to Elevated Glomerular Filtration in Diabetic Children
Authors: Ditzel Jørn , Brøchner-Mortensen Jens
Published: September 2013

To study renal tubular reabsorption and tubulo-glomerular balance in diabetic children, glomerular filtration rate (GFR) and tubular reabsorption rates of sodium, glucose, ultrafilterable calcium, and phosphate were measured during fasting in 26 ambulatory type I (insulin-dependent) diabetic children without clinical signs of microangiopathy (age 7–14 yr; duration of diabetes 3–14 yr). Similar measurements were made in 28 healthy school children (age 8–14 yr). Mean GFR in the diabetic children was significantly higher than in the normal children (138 versus 109 ml/min/1.73 m2, P < 0.01). Mean tubular reabsorption rates of sodium, glucose, and calcium were significantly increased in the diabetic subjects (P < 0.001). In contrast, tubular reabsorption rate of phosphate in the diabetic subjects was not enhanced. The renal threshold concentration of phosphate (TmPO4/GFR) was suppressed in the diabetic compared with the healthy subjects (1.23 versus 1.73 mmol/L, P < 0.001). TmP04/GFR was unrelated to circulating parathyroid and growth hormone concentrations but correlated inversely with the reabsorption rate of glucose (r = -0.53, P < 0.01). Sodium reabsorption was closely correlated to GFR in both diabetic (r = 0.99, P < 0.0001) and healthy subjects (r = 1.00, P < 0.0001), and both groups showed identical regression lines. The tubular glucose reabsorption rate was independent of GFR in the diabetics. Tubular calcium and phosphate reabsorptions correlated equally well with sodium reabsorption and with GFR in the diabetic and healthy subjects (P < 0.001). The maximal reabsorption of phosphate relative to GFR was lowered in the diabetic children. Thus, in the diabetic subjects, the tubulo-glomerular balance was maintained for sodium, but not for phosphate.

These findings can be interpreted as a consequence of increased plasma (and ultrafilterate) glucose concentration inhibiting maximal phosphate reabsorption, leading to a stimulation of sodium coupled glucose reabsorption (cotransport), and thereby of solutelinked water reabsorption. The normalization of absolute phosphate reabsorption may be a consequence of the increased reabsorption of sodium. The excess sodium/solute-linked reabsorption is likely to be basic for the mechanism leading to the elevated GFR in the diabetic subjects.
Mechanisms of Proteinuria in Diabetic Nephropathy II: A Study of the Size-Selective Glomerular Filtration Barrier
Authors: Friedman Stuart , Jones Henry W , Golbetz Helen V , Lee Jeri A , Little Hunter L , Myers Bryan D
Published: September 2013

We evaluated the size-selective properties of the glomerular barrier in 30 patients in whom diabetic nephropathy was associated with urinary IgG losses. Neutral dextrans of graded size were used to characterize glomerular membrane-pore structure. A fractional IgG clearance (relative to freely permeable inulin) smaller or greater than 0.001 was used to distinguish patients with minor (group 1, N = 14) and major (group 2, N = 16) urinary IgG leakage, respectively. Fractional clearances of dextrans (θD) of smaller size (radii 20–40 Å) were similar, but those of larger dextrans (radii 42–60 Å) were elevated in group 2 relative to group 1 patients. When plotted on log-normal probability coordinates, the correlation between θD and radius in healthy subjects is linear, suggesting that glomerular pores form one population with a normal distribution. In diabetic nephropathy with urinary IgG leakage, however, θD for large molecules was elevated and departed from linearity, suggesting a bimodal pore size distribution within the glomerular membrane. A pore model of solute transport revealed (1) the upper pore mode was highly permeable to large dextrans equivalent in size to IgG and (2) the fraction of glomerular filtrate permeating the large pores was greater in group 2 than in group 1 patients with diabetic nephropathy, 6% versus 3%, respectively. We conclude that urinary IgG leakage in diabetic nephropathy is determined by the development of a subpopulation of enlarged pores. The magnitude of urinary IgG losses appears to be a function of the membrane area-fraction occupied by the enlarged pores.
Platelet Enzyme Activities in Diabetes Mellitus in Relation to Endothelial Damage
Authors: Janka H U , Standl E , Schramm W , Mehnert H
Published: September 2013

Increased platelet reactivity has been suggested in the pathogenesis of both arteriosclerosis and diabetic microangiopathy. Therefore, platelet function and platelet enzyme activities were assessed in a large group of 357 diabetics (256 patients with IDDM, aged 16–49 and 101 patients with NIDDM, aged 50–78) and 163 matched controls, and related to photographically documented retinopathy (Rd) and to peripheral vascular disease (PVD) as well as to plasma levels of von Willebrand factor (VIII R:Ag) as an indicator of endothelial damage.

Patients with IDDM had increased platelet aggregation (PA, expressed as μM ADP threshold concentration) before Rd was detectable in comparison to control subjects (P < 0.01). PA was further increased in patients with advanced Rd (P < 0.01), whereas 20 newly diagnosed diabetics with IDDM exhibited normal PA. Patients with minimal Rd did not differ from patients without Rd. Plasma β-thromboglobulin (reflecting platelet consumption in vivo) was enhanced significantly in patients with Rd only (P < 0.05), as was malondialdehyde (MDA) production of platelets (as a measure of platelet endoperoxide formation).

Factor VIII-related antigen in plasma was already increased in patients without Rd (P < 0.05), yet more so in patients with Rd (P < 0.01). Prostacyclin-stimulated adenylate cyclase activity (ACA) of platelets (as an antiaggregatory enzyme system) was twice as high in diabetics with advanced Rd compared with patients without Rd and with controls (P < 0.01). Significant correlations were found between PA and plasma F VIII R: Hg, MDA production, and ACA of platelets.

Increased PA was also found in subjects with NIDDM (P < 0.05). Patients with PVD, however, did not differ from patients without PVD when subjects with Rd were excluded.

These results indicate that increased platelet activity may precede clinically detectable vascular disease, but is associated with increased levels of plasma von Willebrand factor protein, suggesting that endothelial damage is already present. Increases of PA platelet enzyme activities and plasma von Willebrand factor are particularly prominent in diabetics with Rd, reflecting highly active and perhaps younger platelets in this condition.
Failure of Infused β-Hydroxybutyrate to Decrease Proteolysis in Man
Authors: Miles John M , Nissen Steven L , Rizza Robert A , Gerich John E , Haymond Morey W
Published: September 2013

Ketone bodies have been suggested to have a proteinsparing effect, since infusion of Na-β-hydroxybutyrate in man decreases plasma alanine concentrations and urinary nitrogen (N) excretion. To test this hypothesis, six normal postabsorptive volunteers were infused with Na-β-hydroxybutyrate for 3 h. Rates of glucose, leucine carbon, and alanine appearance and disappearance from the plasma space were traced with [3-3H]glucose, L-[6,6,6-2H3]leucine, and [2,3,3,3-2H4]alanine. Rates of leucine N appearance and disappearance and the rate of transfer of leucine N to alanine were assessed with [15N]leucine. During ketone body infusion, plasma alanine decreased (P < 0.05), whereas plasma leucine increased (P < 0.05). Rates of alanine appearance increased (5.3 ± 0.3 to 7.8 ± 0.6 μmol/kg · min), but the increase in its rate of disappearance was sightly greater, accounting for the decrease in plasma alanine concentration. Leucine N flux and the rate and percent of leucine N transferred to alanine increased, whereas leucine carbon flux was unchanged. To determine the effect of the alkalemia induced by Na-β-hydroxybutyrate, four additional subjects were infused with NaHCO3. Alkalemia had no effect on leucine N or carbon flux or on the rate of appearance of alanine, but increased the rate of alanine disappearance, resulting in a decrease in the plasma alanine concentration. Since the rate of appearance of leucine carbon was unaltered during the infusion of Na-β-hydroxybutyrate, it is unlikely that hyperketonemia per se decreases proteolysis in postabsorptive man.
Simulating the Diabetic Environment Modifies In Vitro Prostacyclin Synthesis
Authors: Jeremy J Y , Mikhailidis D P , Dandona P
Published: September 2013

To explain the contradictory data on the secretion of prostacyclin (PGI2) in clinical and experimental diabetes, we have investigated the effect of each of the major metabolic abnormalities in uncontrolled diabetes on vascular PGI2 synthesis. An increase in fatty acid concentrations caused a dose-dependent inhibition of PGI2 synthesis by rat aortic rings in vitro; linoleic and linolenic acids were consistently the most and palmitic the least inhibitory. Glucose had a stimulatory effect between 10 and 30 mmol/L, but a progressive fall in stimulation occurred at higher concentrations. Insulin was inhibitory at 10 and 50 mU/L; however, in combination with glucose (10 mmol/L) it was significantly stimulatory (at 10 mU/L) when the aortic rings were preincubated for 2 and 4 h. A pH of 7.0 or less was significantly inhibitory, whereas ketone bodies had no significant effect on PGI2 synthesis. These data show for the first time that altered metabolic factors in uncontrolled diabetes may have different effects on vascular PGI2 synthesis. These data help explain the variability of observations related to PGI2 synthesis and secretion in diabetes, and advocate a more detailed definition of the metabolic status of patients/animals used in such experiments.
Influence of Glucose on Insulin Handling by Rat Islets in Culture: A Reflection of Integrated Changes in Insulin Biosynthesis, Release, and Intracellular Degradation
Authors: Halban Philippe A , Renold Albert E
Published: September 2013

Rat islets were maintained for 3 days in tissue culture at 2.8, 8.3, or 16.7 mM glucose, in the presence of [3H]leucine to label insulin stores. The immunoreactive insulin content of islets after 3 days at either 2.8 or 16.7 mM glucose was lower than that of islets exposed to 8.3 mM glucose. The specific radioactivity of stored labeled insulin, however, increased with increasing glucose. Islet insulin turnover was thus highest at 16.7 mM glucose. During a subsequent 1-day chase period at 2.8, 8.3, or 16.7 mM glucose for each of the three groups of islets prelabeled at these same three concentrations, all islets responded to glucose with increased insulin release. Release of immunoreactive insulin was highest at all three chase glucose concentrations for those islets preexposed for 3 days to 16.7 mM glucose. After 3-day labeling of islets at 8.3 mM glucose, there was an inverse relationship between the rate of release of labeled insulin and its intracellular degradation in response to the three glucose concentrations during the chase period. Those islets prelabeled at either 2.8 or 16.7 mM glucose showed much lower rates of intracellular degradation of labeled insulin stores during the chase period regardless of the ambient glucose or of the rate of release of the labeled hormone.

Adaptive changes in islet insulin handling thus occurred during the 3-day maintenance period at different glucose concentrations. Whereas glucose concentration is, of course, thought to regulate insulin biosynthesis and release directly, regulation of degradation of stored insulin within B-cells appears to reflect both the relative activity of biosynthesis and release of the hormone and the insulin content of the islets. This last and striking relation is best interpreted as reflecting two labile, exchangeable, granule pools, one preferentially available for release and the other for intracellular degradation.