bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for an Effect of Exorphins on Plasma Insulin and Glucagon Levels in Dogs
Authors: Schusdziarra V , Henrichs I , Holland A , Klier M , Pfeiffer E F
Published: September 2013

Recently, peptides with opioid-like activity have been demonstrated in peptic digests of dietary protein. The present study was designed to determine the effect of digested and undigested gluten on postprandial insulin and glucagon levels in conscious dogs. The intragastric instillation of digested gluten (25 g) elicited a more rapid and a significantly greater rise in postprandial peripheral vein insulin and glucagon levels compared with the effect of 25 g undigested gluten. The incremental insulin level was 104 ± 20 μU/ml after digested gluten and only 58 ± 7 μU/ml (P < 0.01) after undigested gluten; the respective values for glucagon are 426 ± 25 pg/ml versus 302 ± 20 pg/ml (P < 0.01). The intragastric administration of naloxone (4 mg), a specific opiate receptor antagonist, reduced the insulin response and augmented the glucagon response to the digested gluten test meal, whereas the response of both hormones to the undigested gluten meal was not affected by naloxone. Intravenously infused naloxone during the digested gluten meal did not influence insulin or glucagon levels. The present data suggest that in dogs the peptic digest of gluten contains an opioid-like material that stimulates postprandial insulin and glucagon release.
Analysis of Glycosaminoglycan from Diabetic and Normal Chinese Hamster Cells
Authors: Ginsberg Leonard C , Wyse Beatrice M , Chang Albert
Published: September 2013

Diabetic and normal cell lines from Chinese hamster kidneys were cultured in media containing 35SO4 and 3H-glucosamine. Glycosaminoglycans (GAG) were extracted and analyzed from the media, trypsin, and cell pellet by enzymatic and electrophoretic procedures. Significant increases in the hyaluronic acid content were noted in all three fractions of diabetic GAGs when compared with normals. In addition, an increased heparan sulfate content and decreased chondroitin sulfate amounts were noted in diabetic cell lines. These data suggest that in vivo changes in GAG types and amounts in diabetic kidneys seen by others may also be seen in cultured cells.
Disappearance of Erythrocyte Insulin Receptors During Maturation in Sheep
Authors: Sinha Madhur K , Ganguli Supriya , Sperling Mark A
Published: September 2013

We studied insulin receptor characteristics and glucose uptake in erythrocytes (RBCs) of sheep during maturation. RBC insulin receptors were characterized with respect to binding of monoiodinated 125I-insulin and by Scatchard analysis to determine binding sites, and their affinities. Glucose uptake by RBCs was assessed by incorporation of 14C-2-deoxy D-glucose in the presence of D-glucose. The percent specific 125I-insulin bound to RBCs from fetal sheep (4.81 ± 0.48 SE; N = 11) was significantly higher when compared with those from 1–7-day-old newborn lambs (3.41 ± 0.24, N = 7). Thereafter, insulin binding progressively decreased to 2.45 ± 0.46 at 8–14 days, 0.99 ± 0.08 at 15–21 days, and 0.41 ± 0.25 at 22–35 days. No specific insulin binding was observed in adult sheep RBCs. When individual percent specific 125I-insulin binding was plotted against age, there was a significant negative correlation (r = −0.79; P < 0.01). Both high (HA) and low (LA) affinity binding sites per erythrocyte were significantly higher in the fetus (HA, 2.2 ± 0.1; LA, 11.6 ± 0.4) compared with those in newborn lambs (HA, 1.3 ± 0.1; LA, 6.4 ± 0.2). Although the association constant (Ka) for HA sites was significantly lower (P < 0.01) for fetal RBCs (2.4 ± 0.1 × 109 M−1) compared with that for newborn RBCs (3.2 ± 0.1 × 109 M−1), no significant difference was observed for LA Ka in both groups. Because of low percent specific 125l-insulin binding after 1 wk of age, accurate competition curves could not be calculated. Glucose uptake by fetal sheep RBCs (53 ± 2 nmol/min/L × 109 cells, N = 6) was significantly higher than that from adult sheep (25 ± 7, N = 7). A negative correlation existed between RBC glucose uptake and the age of the animals. Although both glucose uptake and insulin receptors decrease postnatally, they appear to be independent phenomena, since insulin (120 μU/ml) did not augment glucose uptake in either fetal cells possessing insulin receptors or adult cells without suchreceptors. We conclude that disappearance of insulin receptors and decreased glucose uptake in sheep RBCs reflect ongoing and independent maturation of membrane function.
Clinical Trial of an Aldose Reductase Inhibitor in Diabetic Neuropathy
Authors: Handelsman D J , Turtle J R
Published: September 2013

A single-blind, nonrandomized, placebo crossover clinical trial of an aldose reductase inhibitor, Alresta-tin (AY 22, 284) was performed over a 4-mo period in nine patients with diabetic peripheral neuropathy. Most patients had subjective benefit, but objective measures of conduction were essentially unchanged. Substantial toxicity was evident, particularly photosensitive Skin rash.
Irreversibility of Glomerular Basement Membrane Accumulation Despite Reversibility of Renal Hypertrophy with Islet Transplantation in Early Experimental Diabetes
Authors: Gøtzsche O , Gundersen H J G , Østerby R
Published: September 2013

A quantitative morphologic study of the glomeruli in rats after 4 wk of streptozotocin-induced diabetes showed a number of glomerular changes, as previously described. Of particular interest was the increase in the total amount of glomerular basement membrane material [from 0.94 ± 0.13 (SD) mm3 to 1.26 ± 0.14 mm3 per kidney]. This parameter did not change after 4 wk of normoglycemia following islet cell transplantation (1.19 ± 0.17 mm3), nor was the total glomerular volume normalized. The contralateral kidney was weighed and used for estimating the total amounts of protein, RNA, and DNA. Four weeks of diabetes expectedly resulted in a 50% increase in kidney weight, and islet cell transplantation diminished this to 15% in excess of normal.

The average cell size (protein/DNA ratio) paralleled the kidney size after diabetes and following transplantation. The average amount of RNA per cell (RNA/DNA) increased significantly after induction of diabetes and was totally normalized after transplantation. Kidney protein concentration (mg protein/mg kidney) remained constant throughout the experiment. Considering that a few weeks of diabetes provokes a large increase in basement membrane material, it is especially noteworthy that 1 mo of normoglycemia is quite insufficient to reverse the accumulation.
Evidence for a New Cause of Defective Plasma Removal of Very Low Density Lipoproteins in Insulin-Deficient Rats
Authors: Bar-On Hanoch , Chen Yii-Der I , Reaven Gerald M
Published: September 2013

These studies were initiated to see if factors other than reduced lipoprotein lipase activity might contribute to the defect in plasma removal of very low density lipoprotein (VLDL) that is observed in insulin-deficient rats. VLDL-triglyceride (TG) was labeled in vivo with 3H-glycerol in control and diabetic rats, and ali-quots of plasma containing 3H-VLDL were injected into normal recipient rats. The half-time (t1/2) of removal was almost twice as long when plasma from diabetic rats was injected, and this was true when the diabetic rats were fed either sucrose or regular chow. A comparable increase in t1/2 was observed when 3H-VLDL isolated from normal rats was recombined with VLDL-free plasma from control and diabetic rats and injected into normal recipients. As before, the changes observed were not dependent upon antecedent diet. However, no significant difference in t1/2 was observed when 3H-VLDL was isolated from control and diabetic rats and injected into normal recipients. Thus, there appears to be a factor present in VLDL-free plasma obtained from diabetic rats that interferes with removal of VLDL from the vascular compartment. Whether this factor is found in diabetic plasma in vivo, or is transferred from diabetic VLDL to diabetic plasma in the isolation procedure, remains to be clarified. In either event, there appears to be a factor, other than reduced LPL activity, that may play a role in the defect of VLDL-TG removal seen in insulin deficiency.
Immunoreactivity and Biologic Activity of Semisynthetic [LeuB30]-Insulin: Potential Value in the Treatment of Insulin Antibody-Mediated Insulin Resistance
Authors: Kobayashi Masashi , Ohgaku Seiji , Iwasaki Makoto , Shigeta Yukio , Oka Tatsushi , Morihara Kazuyuki
Published: September 2013

Insulin analogues with different amino acids, including threonine, alanine, L-leucine, D-leucine, L-leucine amide, phenylalanine, tri-alanine, or desalanine, at the B-30 position were semisynthesized from pork insulin by the new enzymatic method. The order of ability of the insulin analogues to bind to anti-insulin sera was [AlaB−30] > desalanine > [ThrB−30] > [Ala-Ala-AlaB−30] > [D-LeuB−30], [Leu-NH2B−30], [PheB−30] > desoctapep-tide > [LeuB−30]. The ability of insulin analogues with different amino acids at B-30 to bind to receptors, as well as their biologic potency tested with glucose uptake in isolated rat adipocytes, was comparable among the analogues. These results suggest that [LeuB−30]-insulin demonstrated the least immunoreactivity and has full activity in receptor binding and biologic effect, and that it may be useful for treatment of anti-insulin antibody-mediated insulin resistance.
Effects of Pregnancy and Sex Steroid Administration on Skeletal Muscle Metabolism in the Rat
Authors: Rushakoff Robert J , Kalkhoff Ronald K
Published: September 2013

To determine whether the insulin resistance, exaggerated fasting hypoglycemia, and hypoalaninemia of late human and rat gestation may reflect altered skeletal muscle metabolism, hindlimbs of nonpregnant (NPG) and 3-wk-pregnant (PG) rats were noncyclically perfused in situ. In 12- and 24-h-fasted NPG rats, 50–500 μU/ml of insulin significantly augmented glucose uptake 3-9-fold. In PG rats uptake was suppressed 40–50% at comparable hormone concentrations. Release of alanine and phenylalanine was suppressed 20–35% by 250 μU/ml or more of insulin in NPG rats. However, comparable insulin concentrations failed to suppress their release in PG rats. No differences between groups existed with respect to oxygen uptake, glycerol, lactate, or pyruvate release. Suppression of insulin sensitivity in 12-day-pregnant rats was not observed.

Since plasma estradiol (E) and progesterone (P) are increased in pregnancy, E-benzoate (5 μg/day) and/or P (5 mg/day) were injected s.c. into female rats for 21 days. In 12-h-fasted animals, E treatment potentiated whereas P treatment mildly antagonized insulin-induced glucose uptake relative to control values. Separate effects of E and P were offset when administered in combination. Individual or combined regimens did not alter oxygen uptake, or release of alanine, phenylalanine, lactate, or pyruvate.

In late gestation, insulin action on skeletal muscle is resisted with respect to glucose uptake, alanine release, and proteolysis. Fasting hypoalaninemia is not due to impaired alanine release from muscle, but may reflect increased fetal extraction. Fasting hypoglycemia may represent, in part, maternal gluconeogenic precursor deficiency due to fetal alanine removal. E and/or P treatment do not duplicate the observed metabolic Changes.
Platelet Aggregation and Release of ATP After Incubation with Soluble Immune Complexes Purified from the Serum of Diabetic Patients
Authors: Van Zile J , Kilpatrick M , Laimins M , Sagel J , Colwell J , Virella G
Published: September 2013

Human platelets are known to have Fc receptors that are able to recognize soluble immune complexes and to respond to that stimulation by aggregating and releasing soluble factors. In diabetes, enhanced platelet aggregation has been proposed as one of the factors contributing to the development of microangiopathy. Soluble immune complexes isolated from seven diabetic patients were found to enhance ADP-induced platelet aggregation and release of ATP. This enhancement was proven not to be an artifact due to the isolation protocol, by comparison of purified immune complexes with nonspecific protein purified from normal sera by identical or slightly modified isolation protocols. Soluble immune complexes appear to be the first well-characterized platelet aggregating factors from the sera of diabetic patients. The nature of the antigen involved in their formation does not appear relevant, since very similar results were obtained whether soluble immune complexes were purified from patients with insulin-anti-insulin complexes in their serum, or from those without such complexes but with positive results in nonspecific screening techniques.
Prospective Study of Insulin-dependent Diabetes Mellitus
Authors: West R , Colle E , Belmonte M M , Tingle A , Guttmann R , Hynie I , Thomas D , Wilkins J , Poirier R , Crepeau M P
Published: September 2013

Laboratory study of 109 insulin-dependent diabetics younger than 17 yr of age and resident in greater Montreal at the time of onset of symptoms is reported. The cases were diagnosed during a 2-yr period (1976- 1978). Sibling controls were obtained for 72 of the cases studied. Viral titers to Coxsackie B, rubella, and mumps viruses for the 72 patient-sibling pairs showed no difference in geometric mean titers or in change of titer between samples taken at the time of diagnosis and those taken 28 days later. The incidence of positive islet cell antibody in the IDDM cases was 68.0% at the time of diagnosis compared with 56.9% 4 wk later. The comparative figures for sibling controls were 4.2% and 1.4%, respectively. The frequency of HLA B8, B15, B18, and B7 antigens were compared both with the sibling controls and a normal control population. Pairings of high risk HLA antigens were found more frequently in cases than controls. There was no difference in geometric mean viral titers in cases with high risk haplotypes compared with those cases in which such haplotypes were absent.
Platelet Aggregation and Coagulation in the Pathogenesis of Diabetic Retinopathy in Rats
Authors: Ishibashi Tatsuro , Tanaka Kenzo , Taniguchi Yoshiaki
Published: September 2013

Fifty male rats were made diabetic by a single injection of streptozotocin and were killed at periods varying from 1 to 12 mo. Ten saline-injected rats and three rats treated with 3-O-methylglucose and streptozotocin served as controls. Intraluminal changes in retinal vessels were studied by electron microscopy. In diabetic rats maintained for 9–12 mo, microthrombus formation was observed in the various sized retinal vessels at the histologic and ultrastructural level. The microthrombi were mainly composed of aggregated platelets and fibrin strands. However, there was no definite evidence of detachment or loss of the endothelial cells. This microthrombus formation may play an important role in the development of diabetic retinopathy.
The Importance of Determining Irreversibly Glycosylated Hemoglobin in Diabetics
Authors: Compagnucci Pietro , Cartechini Maria G , Bolli Geremia , Feo Pierpaolo De , Santeusanio Fausto , Brunetti Paolo
Published: September 2013

The concentration of glycohemoglobins (HbA1(a+b+c), HbA1,) was measured before and after incubation of normal and diabetic erythrocytes for 6 h at 37°C in saline. This procedure removes as much as 80-90% of the labile glucose-HbA0 adduct (labile HbA1,), thus allowing accurate estimation of irreversibly glycosylated hemoglobin (stable HbA1,). The concentration of HbA1 measured before such an incubation is total HbA1, (stable + labile). We determined the concentration of total, stable, and labile HbA1, in the same blood samples used to measure fasting plasma glucose (FPG) every day, for 4 consecutive days, in two groups of hospitalized insulin-treated diabetics. Group A subjects (N = 7) were type I, C-peptide negative, unstable diabetics, while group B subjects (N = 15) were type II, C-peptide positive, stable diabetics. Individual day-to-day variations of total HbA1, were wide in group A (Δ = 1.58 ± 0.14%), and slight in group B (Δ = 0.12 ± 0.01%; P < 0.001), paralleling similar plasma glucose fluctuations. Day-to-day variations of stable HbA1, were virtually absent not only in group B subjects with stable glycemic values (Δ = 0.08 ± 0.01%), but also in those of group A with marked glycemic instability (Δ = 0.07 ± 0.01%; P = NS). Day-to-day variations of labile HbA1, were marked in group A (Δ = 1.31 ± 0.14%), but negligible in group B (Δ = 0.15 ± 0.03%; P < 0.001). On admission, FPG correlated with labile HbA1, in group A (r = 0.89) and B (r = 0.71). FPG correlated with stable HbA1, in group B (r = 0.73) but not in group A subjects and with total HbA1, more closely in group B (r = 0.73) than in A (r = 0.61). A very close correlation was found between the concentration of total and labile HbA1 in subjects of group B (r = 0.82). In group B, fasting, post-breakfast, and mean daily plasma glucose values, determined every 3-6 days during the 2 mo before admission, significantly correlated both with total and stable HbA1 determined on admission, while in group A they did not. In group A, the correlation was significant when stable instead of total HbA1 was considered. We conclude that the significant fluctuations of total HbA1 reduce its value as an index of long-term control in unstable diabetics. On the other hand, a single determination of stable HbA1, totally independent of simultaneous blood glucose values, closely reflects blood glucose control over the previous 2 mo. We propose routine estimation of stable HbA1, which is simple and straightforward, to carry out follow-up studies of unstable diabetics.
Myo-lnositol and the Maintenance of β-Cell Function in Cultured Rat Pancreatic Islets
Authors: Pace Caroline S , Clements Rex S
Published: September 2013

We studied the effect of the myo-inositol content of culture media on several of the functional characteristics of cultured adult rat pancreatic islets. Variations in the ambient myo-inositol concentration had no effect on insulin content, its rate of synthesis, or its secretion in response to glucose when studied in freshly isolated islets. However, myo-inositol did inhibit the incorporation of 3H-thymidine into the DNA of the fresh islet. When islets were cultured for 6 days in the absence of myo-inositol, their basal rate of insulin secretion was elevated and they were unresponsive to an elevated glucose concentration. As the myo-inositol content of the culture medium was increased from 10 to 40 μg/ml, a progressive decrease in basal insulin secretion as well as an increase in glucose-stimulated insulin secretion was observed. Similarly, the total insulin content of cultured islets increased progressively as the myo-inositol content of the culture medium was raised. The rates of incorporation of 3H-leucine into islet protein, proinsulin, insulin, and Cpeptide were found to be twice as high in the presence of 40 μg/ml myo-inositol when compared with the rates observed in the absence of this material. The incorporation of 3H-thymidine into the DNA of cultured islets was maximal when the medium contained 20 μg/ml myo-inositol, and was decreased when concentrations above or below this value were employed. These results demonstrate that the ambient myo-inositol concentration to which cultured islets are exposed in vitro exerts a strong influence on their functional characteristics. Thus, the myo-inositol content of the culture media employed should be taken into consideration in the interpretation of any studies involving cultured pancreatic islets.
Diabetes Induced with Multiple Subdiabetogenic Doses of Streptozotocin: Lack of Protection by Exogenous Superoxide Dismutase
Authors: Gold Gerald , Manning Michele , Heldt Anneliese , Nowlain Robert , Pettit James R , Grodsky Gerold M
Published: September 2013

The addition of exogenous superoxide dismutase (SOD) was examined as a possible means of protecting B-cells of mice against either the immediate or delayed toxicity caused by multiple injections of low doses of streptozotocin (Sz). Three different routes of SOD administration (i.p. and i.v. injection and continuous s.c. infusion) and several different doses and schedules were tried. In addition, a long-acting derivative of SOD was synthesized and tested. Despite the observation of a modest delay in the onset of diabetes in one experiment, no protective effect of SOD on the progressive elevation of blood glucose concentrations was evident in the majority of studies. Moreover, a loss in pancreatic insulin content and a tripling of pancreatic glucagon content occurred in all mice treated with low dosages of Sz, irrespective of whether or not either SOD or a long-acting derivative of SOD was administered. Finally, in parallel experiments in vitro, this enzyme was ineffective in protecting isolated rat islets from the acute toxicity of exposure to Sz on glucose-stimulated insulin release.
Insulin and Glucagon Breakthrough of Somatostatin Suppression: Importance of Portal Vein Hormone Measurements
Authors: Polonsky K , Jaspan J , Pugh W , Dhorajiwala J , Abraham M , Bux P , Moossa A R
Published: September 2013

The infusion of somatostatin (800 ng/kg/min) into anesthetized dogs leads to suppression of portal insulin concentrations from 58 ± 5 μU/ml to 18 ± 5 μU/ml and peripheral arterial concentrations from 18 ± 2 μU/ml to 8 ± 2 μU/ml, these levels remaining suppressed for the duration of the infusion (210 min). Additional experiments were performed during which somatostatin (800 ng/kg/min) was infused alone for 30 min and then together with glucose to reach steady-state glucose concentrations of 422 ± 8 mg/dl. This hyperglycemic stimulus resulted in progressive increments in portal insulin of 15 ± 3, 22 ± 8, 41 ± 11, 62 ± 14, 77 ± 17, and 88 ± 6 μU/ml at successive 10-min intervals. The corresponding increments in arterial insulin were much less, being 5 ± 2, 4 ± 1, 5 ± 2, 8 ± 2,10 ± 4, and 19 ± 6 μU/ml. In separate experiments, the rate of glucose infusion was varied so that steady-state glucose concentrations of 173 ± 3, 255 ± 8, and 359 ± 5 mg/dl were achieved in successive 60-min periods. Portal vein insulin values in each period were 100 ± 34, 262 ±117, and 596 ± 162 μU/ml, with corresponding peripheral levels of 12 ± 6, 26 ± 14, and 69 ± 45 μU/ml, respectively. Similar experiments in which a lower dose of somatostatin was used (200 ng/kg/min), in the face of similar steady-state glucose increments, resulted in portal insulin levels of 182 ± 62, 435 ± 138, and 512 ± 102 μU/ml, and corresponding peripheral levels of 34 ± 15,141 ± 55, and 188 ± 20 μU/ml, respectively.

Somatostatin infusion (800 ng/kg/min) suppressed portal vein glucagon levels to 101 ± 16 and peripheral levels to 39 ± 3 pg/ml. In these animals, hypoglycemia was then induced by infusion of insulin, and portal and peripheral glucagon levels rose to 341 ± 11 and 146 ± 27 pg/ml, respectively.

Thus, the inhibition of insuiin and glucagon secretion by pharmacologic doses of somatostatin may be overcome by an appropriate stimulus. Because of the large capacity of the liver for insulin extraction, increases in portal insulin levels may not be reflected in the periphery. However, increases in portal vein glucagon, although underestimated from peripheral levels, were always associated with changes in peripheral levels, because the liver extracts less glucagon than insulin. These findings should be considered in the interpretation of experimental studies in which somatostatin has been used to suppress endogenous pancreatic hormone secretion and peripheral hormone levels alone are used to monitor the adequacy of suppression.
Regulation of Ornithine Decarboxylase in Skeletal Muscle: Evidence for the Involvement of an Insulin-dependent Serum Factor
Authors: Conover Cheryl A , Jaime Rozovski S , Ruderman Neil B
Published: September 2013

Previous studies in vivo have shown that the activity of ornithine decarboxylase (ODC), the rate-controlling enzyme in polyamine biosynthesis, is markedly decreased in muscle of diabetic rats and is restored to normal by insulin therapy. Also, muscle ODC is diminished by starvation and increased by refeeding. To investigate the basis for these findings, the regulation of ODC was studied in vitro using rat soleus and extensor digitorum longus muscles. Incubation of muscles from fed rats in Krebs-Henseleit solution resulted in a 75% decrease in ODC activity within 1 h. Addition of insulin and amino acids had no effect; however, 50% rat serum increased ODC activity four- to sevenfold after the initial decrease. Rat serum also increased ODC in muscles from starved rats. The effect of serum was blocked by both cycloheximide and actinomycin D. Serum from diabetic rats was only 50% as effective as serum from normal rats in increasing ODC activity. Addition of physiologic levels of insulin to diabetic serum had no effect; however, treatment of diabetic rats with insulin in vivo restored serum activity to normal. These findings suggest that insulin modulates the synthesis of ODC via production of a second circulating factor, the activity of which is diminished in serum of diabetic rats. They also suggest that the stimulation of polyamine biosynthesis by this factor may be an integral component of the growth-promoting effect of insulin on muscle in vivo.
The Mechanism of Impaired T3 Production from T4 in Diabetes
Authors: Gavin Laurence A , McMahon Francis A , Moeller Marie
Published: September 2013

Uncontrolled diabetes in man is associated with low serum T3 values and impaired production of T3 from T4. Because the thiol-dependent enzyme T4-5′-deiodinase catalyzes T4-deiodination to T3, the present study was conducted to determine whether these alterations in iodothyronine metabolism consequent to diabetes were due to a reduction in the tissue content of active enzyme or thiol cofactor availability. T4-5′- deiodinase activity and nonprotein sulfhydryl (NP-SH) groups were examined in liver homogenate preparations from groups of rats (T4-treated) diabetic (streptozotocin, 100 mg/kg i.p.) for 48-96 h and compared with controls.

The mean hepatic T4-5′-deiodinase activity in the control group was 4.8 ± 0.4 pmol/min/100 mg protein (mean ± SEM). In each of the diabetic groups (48, 72, and 96 h), the mean enzyme activity was significantly less (P < 0.005) than the control mean. Homogenate enrichment with the thiol reagent dithiothreitol (DTT) (5 mM) failed to reverse this diabetic effect. Moreover, although the hepatic content of NP-SH groups was significantly less than the controls after 48 and 72 h of hyperglycemia, it had spontaneously reverted to normal by 96 h. Thus, the impaired enzyme activity could not be attributed to a deficiency of thiol cofactors.

The dissociation between enzyme activity and tissue sulfhydryl groups was further illustrated by the response to insulin treatment. Insulin was given by continuous s.c. infusion to 48-h diabetic rats for 48-96 h. Although insulin therapy normalized both enzyme activity and the hepatic thiol content, the temporal profile of each response was different. Insulin therapy rapidly (48 h) corrected the hepatic content of NP-SH groups, whereas the normalization of T4-5′-deiodinase activity required 72-96 h of insulin treatment.

There was a positive correlation (r = + 0.69, P < 0.025) between the serum T3 values and hepatic T4-5′-deiodinase activity. The mean serum T3 concentration was significantly reduced (P < 0.001) by the diabetes after 48 h and remained low at 72 and 96 h. Insulin treatment reversed this defect but, as in the case of enzyme activity, the normalization was delayed until 72-96 h of insulin therapy.

These results indicate that (1) diabetes reduces serum T3 levels and hepatic T4-5′-deiodinase activity in T4-treated rats, (2) T4-5′-deiodinase is probably the major regulator of serum T3 levels under these conditions, and (3) the reduced T4 -5′-deiodinase activity is independent of changes in the hepatic content of NPSH groups and probably reflects a reduction in the hepatic content of active enzyme.
A Rapid Chemical Means for Removing Labile Glycohemoglobin
Authors: Nathan David M , Avezzano Eric S , Palmer John L
Published: September 2013

We have devised a rapid and convenient method of eliminating the contribution of labile glycosylated hemoglobin in the hemoglobin A, assay. The procedure requires a 30-min incubation of erythrocytes in 30 mM semicarbazide and 12 mM aniline (pH 5, 38°C). This chemical means of eliminating the labile fraction is as effective as a 14-h incubation in isotonic saline as measured with high-pressure liquid chromatography or electrophoresis methods. The removal of the labile glycosylated hemoglobin fraction preserves the assay as a reliable index of chronic metabolic control.
Characterization of Insulin-induced Receptor Loss and Evidence for Internalization of the Insulin Receptor
Authors: Marshall Stephen , Olefsky Jerrold M
Published: September 2013

We studied the relationship between insulin-induced receptor loss and insulin internalization in isolated rat adipocytes. When cells were exposed to 100 ng/ml insulin at 37°C for times ranging from 10 min to 6 h, a monoexponential loss of insulin receptors was observed for up to 4 h, with a t½ of 75 min and a 75% maximal loss. The insulin-induced loss of receptors was dose-dependent with a % maximal effective insulin concentration of 7.6 and 1.3 ng/ml in 2- and 6-h insulin- pretreated cells, respectively. The ability of insulin to mediate receptor loss was inhibited by low temperature (16°C) and by the metabolic energy depleters dinitrophenol and NaF, suggesting that receptor loss is mediated by an 125I-insulin compared with control cells, and the relationship between insulin-induced receptor loss and insulin internalization was assessed by comparing these two processes over time and as a function of temperature. Using this approach, a significant linear relationship was observed between these partners at various temperatures (r = 0.99) and times (r = 0.94). These results suggest that the mechanism whereby insulin induces receptor loss in adipocytes is by internalization of insulin-receptor complexes.

Insulin receptors remaining on 2-h insulin, pretreated cells had identical dissociation rates and exhibited similar negative cooperative interactions when compared with control cells. Furthermore, anti-insulinreceptor antibodies inhibited binding in both groups of cells to the same extent. In contrast to these similarities, insulin-induced receptor loss was accompanied by a progressive impairment in the ability of cells to accumulate intracellular insulin in the presence ofchloroquine, which we interpret as an insulin-induced slowing of insulin internalization.

In conclusion, (1) insulin causes a time-, temperature-, dose-, and energy-dependent loss of cell-surface insulin receptors; (2) the rate of receptor loss and the extent of insulin internalization are closely correlated, suggesting that insulin-induced receptor loss in adipocytes is mediated by endocytosis of insulin-receptor complexes; and (3) insulin-induced receptor loss is accompanied by a reduced ability of residual receptors to internalize insulin.
Evidence for Transformation of Glucagon-Like Immunoreactivity of Gut into Pancreatic Glucagon In Vivo
Authors: Korányi L , Péterfy F , Szabó J , Török Angela , Guóth Maria , Tamás Gy
Published: September 2013

The effect of gut glucagon-like immunoreactivity (GLI) devoid of pancreatic glucagon was studied in piglets. All glucagon-like peptides with an accessible C-terminal were removed from the gut extract by specific antibodies reacting with the C-terminal of the glucagon molecule. Endogenous secretion of pancreatic and gut glucagon was blocked by somatostatin infusion, and then the purified gut glucagon preparation was infused. The latter prevented the hypoglycemia resulting from somatostatin infusion, and increased the glucagon level detectable by C-terminal specific antibodies in the blood of the animals. This rise was significant statistically from the 30th min of GLI administration (26.7 ± 7.2 pg/ml versus 137.0 ± 67.0 pg/ml; P < 0.05) and increased until the end of the infusion (90th min, 218 ± 60 pg/ml; P < 0.005). It has been suggested that, owing to the in vivo enzymatic degradation of the infused gut glucagon, biologically active “pancreatic” glucagon fractions are formed extracellularly.
Pulsatile, Synchronous Basal Insulin and Glucagon Secretion in Man
Authors: Lang D A , Matthews D R , Burnett M , Ward G M , Turner R C
Published: September 2013

The basal plasma insulin, glucagon, and glucose concentrations of 28 normal subjects were measured at 1-min intervals for periods of 45–120 min. Regular plasma insulin and/or glucagon cycles were detected in 11 subjects by autocorrelation (mean periods 13.1 and 13.7 min, respectively). Individual plasma insulin cycles were defined in all subjects (mean period 10.7 min, amplitude 1.1 mU/L), and were associated, after averaging, with plasma glucagon (amplitude 5.5 pg/ml) and plasma glucose (0.02 mmol/L) cycles. There was a significant correlation between the amplitudes of simultaneous plasma insulin and glucagon cycles (r = 0.23, P = < 0.05, N = 124). Cross-correlation demonstrated a delay of 2 min between the changes in plasma insulin and glucagon. No comparable oscillations in plasma pancreatic polypeptide were detected. The synchronous pulsatile secretion of glucagon and insulin may be a mechanism by which insulin's hepatic effects are limited, thereby maintaining hepatic glucose production but allowing sufficient peripheral insulin concentrations to inhibit excessive catabolism. The simultaneous pulses of insulin and glucagon may be stimulated by a pacemaker, with the A-B intercellular connections producing insulin and glucagon synchrony.
Maturation of Liver Handling of Insulin in the Rat Fetus
Authors: Sodoyez-Goffaux F , Sodoyez J C , Vos C J De
Published: September 2013

Purified carrier-free 125I-Tyr insulin (125I-Tyr Ins) was injected into the vitelline vein of rat fetuses in utero after 17, 19, or 21 days of gestation. Three minutes later, a radioactivity concentration index (RCI) was calculated by dividing the specific activity of each organ by that of the feto-placental unit. The highest RCI were found in the liver (4.09, 5.97, and 6.48, respectively after 17, 19, and 21 days of gestation). Binding of 125I-Tyr Ins to the liver was inhibited by coinjection of excess unlabeled insulin. Sequential injections of 125I-Tyr Ins followed by excess unlabeled insulin demonstrated that 125I-Tyr Ins binding to the liver was but partly reversible and allowed us to calculate that the half-life of the tracer in the whole body receptor compartment was 6 min in 21-day postcoitum fetuses. After extraction and chromatographic analysis, liver radioactivity appeared composed of undamaged 125I-Tyr Ins and low mol. wt. degradation products (125I- and 125I-tyrosine). Liver maturation was characterized by an enhanced capacity to degrade 125I-Tyr Ins and to expel low mol. wt. radioactive products out of the cells. Autoradiographic studies demonstrated that 125I-Tyr Ins was bound in a saturable manner to the hepatocytes and, to a lesser extent, to the liver hematopoietic cells. Three minutes after the tracer alone, silver grains were predominantly associated with the hepatocytes′ plasma membranes. Later, the percentage of internalized grains increased. Because the percentage of liver radioactivity identified as low mol. wt. radioactive products was always smaller than that of internalized silver grains, true 125I-Tyr Ins was actually internalized in the hepatocytes. The rate of 125I-Tyr Ins translocation from the membrane into the cytoplasm increased with the degree of liver maturity. It is concluded that during the last 5 days of gestation, liver maturation concerns insulin internalization and degradation, i.e., postreceptor steps rather than receptor ontogenesis.
Impaired Phagocytic Function and Increased Immune Complexes in Diabetics with Severe Microangiopathy
Authors: Iavicoli M , Mario U Di , Pozzilli P , Canalese J , Ventriglia L , Galfo C , Andreani D
Published: September 2013

An increase in circulating immune complexes (AgAb) of medium size has been observed in diabetics with late complications. This increase may be related either to an increased formation or reduced clearance. Alternatively, both mechanisms may be involved.

As medium-sized AgAb determined by the C1q solid phase method are mainly removed from circulation by the fixed phagocytes of the reticulo-endothelial system, we investigated the function of these cells using a colloid clearance test in diabetics with various degrees of microangiopathy. Microaggregated iodinated human serum albumin was injected into 30 diabetic volunteers with severe (group 1), moderate (group 2), and absent (group 3) microangiopathy, and into 40 normal volunteers.

The colloid clearance was significantly reduced in diabetics with severe microangiopathy in comparison with patients who had no sign of microangiopathy, or with normal subjects. A significant correlation was found between reduced colloid clearance and increased levels of circulating AgAb determined by C1q solid phase method. Results of this study suggest that the increase in circulating AgAb observed in patients with severe microangiopathy may result from an impaired function of fixed phagocytes.
The Chinese Hamster as a Model for the Study of Diabetes Mellitus
Authors: Gerritsen George C
Published: September 2013

Selection for and against diabetes and subsequent inbreeding of Chinese hamsters started in 1963. Currently there are six inbred sublines that have greater than 85% incidence of glycosuria and two control inbred nondiabetic sublines that are essentially free of glycosuria. At birth, hamsters from inbred sublines are considered prediabetic. There is phenotypic variation between diabetic sublines. Onset time, incidence of ketonuria, blood glucose, plasma insulin, glucagon and glycohydrolase levels vary from subline to subline, but pancreatic insulin and glucagon levels are consistently low and high, respectively, in all diabetic sublines compared with nondiabetics. Experimental breeding data suggest a minimum of two homozygous recessive genes for diabetes. It is not known if the inbred lines are similar diabetic genotypes, but the probability is high that modifier background genes vary from subline to subline.

Chinese hamsters have diabetes ranging from mild to severe. Animals weighing 25 g can excrete up to 75 ml of urine containing 3 g of glucose per day. Fasting blood glucose as high as 500 mg/dl and 10 μmol/ml of beta-hydroxybutyrate have been reported. Gluconeogenesis is elevated, and some glycolytic enzymes are decreased in severe diabetes. Low levels of renal acid glycohydrolase enzymes may contribute to glomerular capillary loop basement membrane thickening in diabetic hamsters. Caloric restriction per se or reduction of dietary fat prevented onset of hyperglycemia and hyperinsulinemia in prediabetics. Morphologic changes have been observed in pancreatic islets, kidney, nerve, blood vessels, eyes, brain, and genitourinary systems of diabetic Chinese hamsters. Pathogenesis of diabetes in this animal appears to be related to an increased demand for insulin. Initially there is a positive response to this demand by beta cells, but exhaustion occurs. This is followed by a decrease in beta-cell mass and relative or absolute insulin deficiency.
Cardiovascular Complications
Authors: Chobanian Aram V , Arquilla Edward R , Clarkson Thomas B , Eder Howard A , Howard Charles F , Regan Timothy J , Williamson Joseph R
Published: September 2013

This report summarizes the current state of knowledge concerning the cardiovascular system in various animal models of diabetes and presents their major strengths and weaknesses for studying the important research questions in the field.

Nonhuman primates have many desirable features for studies on the macrovascular and cardiac complications of the disease as well as risk factor alterations, but their availability, cost, and maintenance present practical disadvantages. The spontaneous rodent models of diabetes currently are not considered very useful for cardiovscular research, but they have not been well characterized with respect to most aspects of their cardiovascular system. Alloxan-diabetic rabbits offer some promise for examining the effects of diabetes on atherogenesis, lipoprotein metabolism, and cardiomyopathy, but additional research is required to validate their usefulness. Insufficient data are available on canine and swine models of diabetes to judge their merits for cardiovascular research.

The Task Force recommends: (1) additional long-term investigations to determine the extent and severity of cardiovascular complications in the well-characterized rodent models and in diabetic rodents with multiple risk factor abnormalities; (2) further studies on the macrovascular disease and lipoprotein abnormalities of the alloxan-diabetic rabbit and the development of rabbit colonies with spontaneous diabetes; (3) increased emphasis on such potentially important but neglected areas of research in diabetic animals as the intramyocardial circulation, adventitial blood vessels, blood pressure, platelet function, blood coagulation, blood rheology, and autonomie nervous function; (4) long-term studies on the influence of control of Hyperglycemic and of insulin therapy on cardiovascular complications in diabetic animals; and (5) encouragement of use of diabetic nonhuman primates for cardiovascular research and institution of measures to increase their supply and availability by expanding current colonies, screening newly imported animals for diabetes, and establishing a visiting scientist's program allowing investigators to study diabetic primates at resource centers.
Effect of Ionophore A23187 on Basal and Insulin-stimulated Sugar Transport by Rat Soleus Muscle
Authors: Hall Solveiga , Keo Lundy , Yu Kin Tak , Gould Michael K
Published: September 2013

The ionophore A23187 (10 micrograms/ml) did not affect the uptake of D-[U-14C]xylose by rat soleus muscle incubated under basal conditions. When muscles were incubated in a Ca2+/Mg2+-free (CMF) medium, A23187 promoted the efflux of intracellular Mg2+ and the efflux of 45Ca from preloaded muscles. Under these conditions, conditions, A23187 inhibited insulin-stimulated sugar transport without affecting 125I-insulin binding by the muscle. A23187 induced a slight fall in muscle ATP (16–18%); this does not appear to be responsible for the inhibitory effect of the ionophore on sugar transport. The inhibitory effect of A23187 was completely abolished when the CMF medium was supplemented with Mg2+ and partially reversed by Mn2+ or Zn2+; supplementation with Ca2+ did not reverse the inhibitory effect of the ionophore. These results suggest that insulin stimulates muscle sugar transport through a mechanism that involves intracellular Mg2+.
Studies on the Regulation of Insulin Binding by Liver Plasma Membranes From Zucker Fatty Rats
Authors: Clark Julia B , Keen Stacey , Clark Charles M
Published: September 2013

The hyperinsulinemia of obese rodents has been associated with a reduced number of hepatic insulin receptors except in hepatocytes from fatty Zucker rats. We isolated liver plasma membranes from 10–11-wk-old lean and fatty Zucker rats, some of which were injected with streptozotocin 2–4 wk earlier. We have determined that although the number of hepatic insulin receptors is not reduced in young hyperinsulinemic fatty Zucker rats, the number of receptors can be increased when the hyperinsulinemia of the fatty rats is reduced by treatment with streptozotocin. In the fatty rats, this reduction in circulating insulin is accompanied by a reduction in plasma triglyceride concentration, consistent with a decreased stimulation of hepatic lipogenesis.

Competitive binding curves for insulin were obtained with isolated liver plasma membranes and 125I-insulin. Analysis of these curves for affinity and number of receptors indicated that the number of insulin receptors was unchanged for the fatty control rats relative to the lean control rats but was increased in streptozotocin-treated animals.

These data indicate that the regulation of hepatic insulin receptors is altered in the young fatty Zucker rat as characterized by a lack of downregulation of hepatic insulin receptors by hyperinsulinemia and an upregulation of hepatic insulin receptors at insulin concentrations higher than those found in lean rats. An altered state of hepatic insulin receptor regulation may be characteristic of developing obesity.
New Perspectives on the Microvasculature of the Islets of Langerhans in the Rat
Authors: Bonner-Weir S , Orci L
Published: September 2013

The vasculature of the islets of Langerhans was studied in rats using methacrylate corrosion casts and islet reconstructions from stained serial paraffin sections. In corrosion casts, which allowed a three-dimensional view of the pancreatic vasculature, all islets had one or two afferent arterioles, which gave off numerous capillaries to form a glomerular-like network. Islets could be grouped in three classes on the basis of size. Moreover, these classes had preferential locations within the vascular tree: the smaller the islet, the more peripheral. In small islets (those less than 160 μm in diameter) efferent capillaries arose from this network and either coalesced at the periphery of the islet or passed through perinsular exocrine tissue before coalescing into venules. However, in intermediate islets (those 160–260 μm in diameter) and large islets (those greater than 260 μm in diameter) efferent capillaries usually coalesced at the edge of the islet forming an extensive fingerlike network of collecting venules over the islet. This suggested that at least in the rat a large amount of the islet tissue is directly drained by venules.

In serial paraffin sections of islets perfused with India ink and stained alternately for B-cells or for non-B-cells, the relation of the blood vessels and the organized array of different cell types making up the islet was discernible. In islets of all sizes, the afferent arterioles entered the islet of all sizes, the afferent arterioles entered the islet at discontinuities of the mantle of non-B-(glucagon, somatostatin, and pancreatic polypeptide) cells. Entering at the B-cell mass, the arterioles broke into capillaries that traversed the B-cell core before passing through the opposite non-B-cell mantle. The afferent capillaries coalesced into collecting venules outside the islet. In intermediate and large islets, the overlying collecting venule network was closely apposed to the mantle.

These anatomic findings indicate that in the rat islet only some of the efferent vessels are part of a insuloacinar portal system and that the afferent vessels reach the B-cell core without passing through the non-B-cell islet tissue.
HLA-A, -B, and -DR Associations in Type I Diabetes Mellitus with Onset After Age Forty
Authors: Pittman William B , Acton Ronald T , Barger Bruce O , Bell David S , Go Rodney C P , Murphy Catherine C , Roseman Jeffrey M
Published: September 2013

It remains to be convincingly demonstrated whether insulin-requiring, ketosis-prone, lean-at-onset, type I diabetics who develop their disease after age 40 have the same disease as the children with similar characteristics. To address this question, we examined the population HLA genetic associations of this group. One hundred forty white, insulin-using diabetics with onset of disease past age 40 yr and 268 normal white controls have thus far been analyzed for HLA type. In the group of patients who were lean-at-onset and/or ketosis-prone (N = 54), there was a significantly increased frequency of DR4 (RR = 4.63; P < 0.01) and significantly decreased frequency of DR2 (RR = 0.18; P < 0.05) after correction. DR4 was also significantly increased after correction (RR = 5.72; P < 0.25) in the subgroup who were both lean and ketosis-prone (N = 23). No significant differences in HLA-DR frequencies were found between the obese and not-ketosis-prone group (N = 69) and controls. No significant associations of HLA-A or-B antigens with either group were observed after correction for the number of antigens tested. To our knowledge, this is the first such study in the United States, and the first demonstrating that late onset diabetics who are lean-at-onset and/or ketosis-prone exhibit HLA-DR antigen associations which are similar to early onset cases.