bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prolonged Hypoglycemic Effect in Diabetic Dogs Due to Subcutaneous Administration of Insulin in Liposomes
Authors: Stevenson Ralph W , Patel Harish M , Parsons John A , Ryman Brenda E 
Published: September 2013

SUMMARY
The biologic action of insulin entrapped in liposomes (phospholipid vesicles) has been investigated following subcutaneous injection to dogs made diabetic with a combination of alloxan and streptozotocin. The fate of the liposomally entrapped material was determined by injecting rats subcutaneously with either 125l-insulin or the labeled polysaccharide 14C-inulin, incorporated in liposomes labeled with 3H-cholesterol.
Injection of liposome insulin (0.75 U/kg) to five diabetic dogs resulted in a mean (± SEM) blood glucose fall from 16.4 ± 0.8 to 2.9 ± 0.4 mmol/L. The glucose level had still not returned to baseline after 24 h and, correspondingly, immunoreactive insulin (IRI) could still be detected in frozen and thawed plasma 24 h after injection. In contrast, the hypoglycemic effect of the same dose of free insulin with or without empty liposomes virtually ended within 8 h and IRI levels returned to baseline by 3 h after injection.
In experiments on rats with liposomally entrapped 125l-insulin or 14C-inulin the proportion of the injected dose of tracer recoverable by excision of the injection site remained constant after about 1 h and 70% of the dose was still fixed in subcutaneous tissue for at least 5 h thereafter. When the plasma collected 3 h after subcutaneous injection of labeled liposomes containing 125I-insulin was passed through a column of Sepharose 6B, 50–75% of the 125I-activity was found in the fractions associated with intact liposomes. One possibility for the persistence of the hypoglycemic effect and of measurable IRI following injection of liposome insulin could be the presence of intact liposomes in the circulation for many hours after absorption had ceased.
Inhibition of Glucagon Secretion by Exogenous Glucagon in the Isolated, Perfused Dog Pancreas
Authors: Kawai K , Unger R H 
Published: September 2013

SUMMARY
To determine if glucagon can inhibit its own secretion, exogenous glucagon was perfused in the isolated canine pancreas at concentrations ranging from 90 to 1050 pg/ml during either stimulation or suppression of endogenous glucagon secretion. When endogenous glucagon secretion was completely suppressed by the addition of 200 mg/dl of glucose to the perfusate, the concentration of glucagon in the venous effluent ranged from 80.8 to 89.9% of the level perfused; these deficits of 10–20% were attributed to uptake and/or degradation of exogenous glucagon by the pancreas. By contrast, when endogenous glucagon secretion was stimulated by perfusing with 10 mM arginine or by glucopenia of 25 mg/dl, there was a significant increase in the glucagon deficit (the efflux glucagon level during glucagon perfusion minus the sum of the pre-perfusion efflux level of endogenous glucagon and the concentration of glucagon perfused); only 60–76% of the expected glucagon concentration was present in the venous efflux. This increase in deficit is assumed to reflect suppression of endogenous glucagon. The glucagon deficit rose progressively with the perfused concentration of glucagon until the deficit reached the approximate level of endogenous glucagon, at which no further increase occurred, suggesting that suppression at that point was complete. To determine if the glucagon-suppressing action of glucagon was mediated by an increase in glucagonstimulated insulin or somatostatin secretion, these hormones were measured in the various experiments. Insulin and somatostatin increased significantly when glucagon was perfused with the glucose arginine-containing solution but did not rise significantly when the glucopenic buffer was used, although suppression of endogenous glucagon was similar in each instance. It is concluded that glucagon suppresses glucagon secretion. Evidence that insulin and/or somatostatin mediate this action could not be obtained.
Evidence for Genetic Admixture as a Determinant in the Occurrence of Insulin-dependent Diabetes Mellitus in U.S. Blacks
Authors: Reitnauer Pamela J , Go Rodney C P , Acton Ronald T , Murphy Catherine C , Budowle Bruce , Barger Bruce O , Roseman Jeffrey M 
Published: September 2013

SUMMARY
In recent years, it has been proposed that genetic admixture may have played a role in the increased frequency of insulin-dependent diabetes mellitus (IDDM) in young U.S. blacks relative to African blacks. In support of this proposal, the similar associations of specific markers of the major histocompatibility complex (MHC) with IDDM in U.S. blacks with respect to U.S. whites have been cited. To determine whether racjal admixture was a factor in the increased prevalence, we did three analyses of admixture. In the first we used nine genetic markers (ABO, Rh, Fy, Hp, Gc, PI, OR, Tfr, and Gm) and determined that there was significantly greater than zero genetic contribution from whites in our sample of U.S. black IDDM patients (9.6 ± 2.3%, P &lt; 0.01) when a sample of U.S. blacks without IDDM was used as one “parental” population. In the next two analyses, we estimated the amounts of genetic contribution from whites in the U.S. blacks with and without IDDM using reported gene frequencies for West African blacks for four genetic markers (ABO, Rh, Fy, and Hp). The estimate of admixture (21.4 ± 2.8%) for the black IDDM sample was greater than that for the U.S. black controls (17.9 ± 2.3%), although the difference was not significant. Our estimate of genetic contribution from whites, 21.4% for black IDDM patients, supports the assumptions of 20% admixture which MacDonald and Rotter and Hodge used to test their respective models for the inheritance of IDDM. These results support the hypothesis that admixture with the white population is, in part, responsible for the increase in prevalence of IDDM seen in U.S. blacks.
Insulin Regulation of Sugar Transport in Isolated Pancreatic Acini from Diabetic Mice
Authors: Williams John A , Bailey Anne C , Preissler Margaret , Goldfine Ira D 
Published: September 2013

Insulin-stimulated sugar transport was studied in isolated pancreatic acini prepared from streptozotocintreated mice. In this tissue, insulin increased the uptake of two nonmetabolized D-glucose analogues, [3H] 2-deoxy-D-glucose (2DG), and [3H]3-O-methyl-D-glucose (30MG), but had no effect on the uptake of [3H] L-glucose. A significant effect of insulin on 2DG uptake was seen at 100 pM, whereas a maximal effect required a concentration of 100 nM. The action of insulin on 2DG uptake was time-dependent; 90 min was required for a maximal hormonal effect. This increase in 2DG uptake was due to a greater than twofold increase in the maximal rate of uptake (Vmax); no significant effects were seen on Km.
The mode of insulin action on sugar transport was investigated further. In pancreatic acinar cells, insulin did not alter either membrane potential or 45Ca2+ efflux, two proposed mechanisms for regulation of sugar transport in other tissues. The action of insulin was not due to either contamination with cholecystokinin (CCK) or an action via the CCK receptor. CCK is known to stimulate sugar transport in isolated pancreatic acini via the elevation of intracellular Ca2+. The effect of insulin on 2DG uptake, however, was additive to that of CCK; conversely, dibutyryl cyclic GMP, a known competitive antagonist of CCK, had no effect on insulin stimulation of 2DG uptake, insulin increased 2DG uptake in the presence of 10 μM puromycin, a concentration sufficient to inhibit greater than 90% of protein synthesis. Dihydrocytochalasin B, a compound known to alter acinar cell motility by disrupting microfilaments, progressively blocked insulin stimulation of 2DG uptake over a drug concentrationrange of 1–15 μg/ml These data suggest, therefore,that the time-dependent increase of sugar transport by insulin is unrelated to electrical potential, 45Ca2+ efflux, and new protein synthesis, but may result from a microfilament-related translocation of glucose carrier sites to the plasma membrane.
The Role of Glucose in the In Vitro Regulation of Cell Cycle Kinetics and Proliferation of Fetal Pancreatic B-Cells
Authors: Swenne Ingemar 
Published: September 2013

To study the cell cycle and regulation by glucose of Bcell proliferation, B-cell-rich pancreatic islets of rat fetuses (22 days gestational age) were maintained in tissue culture at various glucose concentrations. The proliferating islet cells were synchronized with hydroxyurea and their rate of progress through the cell cycle studied by pulse labeling with 3H-thymidine and after exposure to colchicine.
The time for a full cell cycle was estimated to 14.9 h and could be subdivided into a G1 phase of a duration of 2.5 h, an S phase of 6.4 h, a G2 phase of 5.5 h, and an M phase of 0.5 h. Although glucose significantly stimulated B-cell proliferation, the progression of cells through the cell cycle was similar at different glucose concentrations. The experiments furthermore suggested that only a limited pool of islet cells was able to proliferate. Glucose seemed to stimulate B-cell proliferation by increasing the number of cells entering the cell cycle.
From the cell cycle data it was possible to calculate the rate of formation of new B-cells, which ranged from 4.2%/24 h in 2.7 mM glucose to 10.4%/24 h in 16.7 mM. When the accumulation of mitotic figures during colchicine treatment was used as an alternative method for estimation of newly formed B-cells the cell birth rates were found to be 3.1 and 6.0%/24 h at 2.7 and 16.7 mM glucose, respectively.
The notion that only a small fraction of B-cells takes part in proliferation would explain the limited regenerative capacity of this cell type. It remains to be established whether such a limitation is of significance in the development of maturity-onset diabetes.
Effects of Experimental Diabetes on Adrenergic and Cholinergic Receptors of Rat Myocardium
Authors: Williams R Sanders , Schaible Thomas F , Scheuer James , Kennedy Rebecca 
Published: September 2013

To more fully characterize the alterations in myocardial adrenergic and cholinergic receptors induced by the diabetic state, we investigated the binding characteristics of (–) [3H] dihydroalprenolol to beta adrenergic receptors (bAR), [3H] prazosin to alpha adrenergic receptors (aAR), and [3H] quinuclidinyl-benzilate to muscarinic cholinergic receptors (MCR) in myocardial membranes derived from rats 8 wk after treatment with streptozotocin. We also studied an equal number of animals from three control groups: free-eating nondi-abetics, pair-weighted nondiabetics, and streptozoto-cin-treated animals treated daily with insulin.
Diabetic hearts demonstrated 27% fewer bAR (P &lt; 0.01) and 31% fewer aAR (P &lt; 0.01) than free-eating controls, without changes in MCR, and without changes in antagonist affinity, agonist affinity, or agonist slope factor (pseudo-Hill coefficient) for any class of receptors. Food restriction had no effect on receptor characteristics, and treatment of diabetic rats with insulin prevented any downregulation of cardiac bAR or aAR.
The parallel decrease in both bAR and aAR suggests that streptozotocin-induced hypothyroidism is not the primary causative factor of bAR downregulation in this model, since hypothyroidism produces upregulation of aAR. Furthermore, the lack of change in cardiac MCR suggests that the adrenergic receptor alterations are not the result of nonspecific abnormalities of protein synthesis in the diabetic heart. Further studies are required to establish the physiologic significance of these receptor alterations, but these data support the hypothesis that altered adrenergic receptor properties may underlie, at least in part, the chronotropic and inotropic abnormalities of cardiac performance that are associated with the diabetic state.
The Adrenergic Contribution to Glucose Counterregulation in Type I Diabetes Mellitus: Dependency on A-Cell Function and Mediation Through Beta2-Adrenergic Receptors
Authors: Feo Pierpaolo De , Bolli Geremia , Perriello Gabriele , Cosmo Salvatore De , Compagnucci Pietro , Angeletti Gabriella , Santeusanio Fausto , Gerich John E , Motulese Mario , Brunetti Paolo 
Published: September 2013

In order to assess the adrenergic contribution to hypoglycemie glucose counterregulation in type | diabetes mellitus and to determine whether the adrenergic contribution is mediated through beta1- or beta2-adrenergic receptors, hypoglycemia was induced by an i.v. insulin infusion (30 mU/m2 · min) for 60 min in 11 insulin-dependent diabetic patients (IDDM), 5 with normal plasma glucagon responses and 6 with blunted responses, and also in 7 age-weight-matched nondiabetic subjects. Rates of plasma glucose decrease and postnadir increase, as well as plasma concentrations of free insulin and of counterregulatory hormones, were measured when insulin was infused alone, and when insulin was infused along with propranolol (a beta1- and beta2-adrenergic receptor antagonist) or metoprolol (a selective beta1-antagonist). Postnadir plasma glucose recovery was decreased in IDDM with blunted plasma glucagon responses (21 ± 0.8 µmol. L−1 min−1, P &lt; 0.001), but was normal in patients with normal plasma glucagon responses (30 ± 0.4 versus 33 ± 0.5 μmol · L−1 · min−1 in nondiabetic subjects, P = NS). Postnadir plasma glucose recovery was not affected by either propranolol or metoprolol in normal subjects and in IDDM with normal glucagon responses. However, in IDDM with blunted plasma glucagon responses, postnadir plasma glucose recovery was further decreased by propranolol (14 ± 0.6 µmol. L−1 min1, P &lt; 0.01), but was unaffected by metoprolol (22 ± 0.9 μmol. L 1 min1, P = NS).
These results demonstrate that, as in normal man, adrenergic mechanisms are not essential for normal plasma glucose recovery from hypoglycemia in IDDM with normal plasma glucagon responses. However, in IDDM with blunted plasma glucagon responses, adrenergic mechanisms become important for glucose counterregulation although they do not fully compensate for the blunted plasma glucagon responses. Since propranolol delayed plasma glucose recovery from hypoglycemia in IDDM with blunted glucagon responses but metoprolol had no effect, the adrenergic contribution to glucose counterregulation appears to be mediated through beta2-adrenergic receptors.
Secretin Inhibits Glucagon in the Isolated Perfused Dog Pancreas
Authors: Hisatomi Akitaka , Unger Roger H 
Published: September 2013

To investigate the effect of secretiti upon islet hormone secretion, highly purified porcine secretin was perfused at 0.0001, 0.001, 0.01, and 0.1 clinical unit (CU)/ml in the isolated normal dog pancreas. The lowest concentration of secretin, a level which is within the physiologic range, significantly suppressed glucagon release and stimulated somatostatin release but was without significant effect on insulin release. At each concentration of secretin tested glucagon was dramatically suppressed and somatostatin was significantly stimulated, both in a dose-dependent manner. B-cell activity was first augmented by the concentration of 0.001 CU/ml (94 pM) of secretin.
These data demonstrate that physiologic levels of secretin suppress pancreatic A-cell activity in the isolated dog pancreas.
Degradation of Insulin Receptors in Rat Adipocytes
Authors: Heidenreich Kim A , Berhanu Paulos , Brandenburg Dietrich , Olefsky Jerrold M 
Published: September 2013

Insulin receptors on viable rat adipocytes were affinity-labeled using a biologically active and photosensitive analogue of insulin, 125I-B2(2-nitro, 4 azidophenylacetyl)-des-PheB1-insulin (125I-NAPA-DP-insulin). The radio-labeled proteins were identified by SDS polyacrylamide gel electrophoresis and autoradiography. Binding of 125I-NAPA-DP-insulin (40 ng/ml) to rat adipocytes at 16°C, followed by photolysis, resulted in the specific labeling of essentially one protein with an apparent molecular weight of 430–450,000 daltons. When this radiolabeled protein was treated with dithiothreitol prior to electrophoresis, specific labeling occurred predominantly in a 125,000-dalton protein and to a lesser extent in a 90,000-dalton protein. In addition, there was a minimal amount of specific labeling of a 115,000-dalton protein. Under certain experimental conditions, the nonreduced form of the photoaffinity-labeled receptor appeared as a heterogeneous population of proteins having apparent molecular weights of 430,000, 350,000, and 270,000 daltons.
Subsequent to photoaffinity labeling of insulin receptors at 16°C, adipocytes were incubated at 37°C for various periods of time to allow for internalization. This resulted in an initial rapid loss of radioactivity in the 430,000- and 125,000-dalton bands. At 60 min the amount of radioactivity in each of these bands was approximately 50% of that present before incubation at 37°C and stayed constant for 120 min. A first-order plot of the decline in receptor-associated radioactivity was biphasic with the initial phase having a half-life of 1.4 h. This loss of radiolabeled receptors was not observed at 16°C and was inhibited by chloroquine (200μM) and cycloheximide (3.5 μM). Under conditions in which approximately 6% of the receptors were photoaffinity-labeled, occupancy of the remaining receptors with insulin had no effect on the degradation of photolabeled receptors. The results suggest that photoaffinity-labeled insulin receptors on viable adipocytes are initially degraded via an endocytotic lysosomal pathway. This pathway of degradation is very rapid and appears to be different from that mediating the basal turnover of unoccupied receptors.
Reduced Solubility of Short-Acting Soluble Insulins when Mixed with Longer-Acting Insulins
Authors: Nolte Martha S , Poon Violet , Grodsky Gerold M , Forsham Peter H , Karam John H 
Published: September 2013

Using insulins from three manufacturers, we examined the recovery by radioimmunoassay of short-acting soluble insulin when mixed with long-acting insulin as a function of the ratio of the mixture and the time of premixing. In ratios of 1:2, 1:3, and 1:5 (short- to long-acting insulin), all Novo, Nordisk, and Lilly short-acting insulins tested showed a significant loss of solubility when mixed with the respective company's long-acting insulin either for less than 75 s or for 20 min before centrifugation.
In ratios of 1:1, Novo's Actrapid (regular) with Monotard (lente) and Lilly's regular with lente showed no significant loss of solubility when pre-mixed for less than 75 s, and the regular insulin also showed no significant loss when pre-mixed for 20 min. However, when Lilly's regular was mixed with either NPH or ultralente in a 1:1 ratio, a significant loss of solubility of the short-acting insulin occurred regardless of time [as was also found with Nordisk's Velosulin (regular) with Insulatard (NPH)].
When Lilly regular was incubated with Lilly lente in ratios of 1:3 for &lt;75 s, 20 min, 4 h, and 24 h before centrifugation, there was a progressive loss of solubility. In contrast, with the same ratios and times of premixing, Lilly regular when mixed with Lilly NPH showed a rapid initial loss of solubility that plateaued by 20 min before centrifugation.
Supernatants from the centrifugation of Lilly's long-acting insulins were assayed and found to contain only 0.67–1.5% of the total insulin content. When Lilly regular was mixed in a 1:3 ratio with these supernatants, there was a small but significant loss of solubility.
These in vitro data indicate that short-acting insulins may lose solubility when mixed with long-acting insulins as the proportion of the latter increases and the time Of pre-mixing iS prolonged.
Do Platelets Have Anything To Do With Diabetic Microvascular Disease?
Authors: Colwell John A , Winocour Peter D , Halushka Perry V 
Published: September 2013

It has been postulated that abnormal platelet and endothelial function may contribute to microangiopathy in diabetes mellitus. If this proposal is correct, alterations in platelet and endothelial function should be found before the appearance of vascular disease in insulin-dependent patients and in animal models of diabetes mellitus. This appears to be the case for the following: platelet aggregation, increased platelet production of the proaggregatory prostaglandin metabolite thromboxane, decreased endothelial production of the antiaggregatory prostaglandin prostacyclin, and decreased platelet survival. Insulin therapy will return some of these findings to normal. Platelet-plasma interactions that promote platelet aggregation and increased plasma levels of the platelet-specific protein β-thromboglobulin have been reported in insulin-dependent diabetic patients who have not manifested vascular complications as well as in those with vascular complications. It has now been demonstrated in animal models that platelet microthrombi are found in small retinal vessels after months of experimental diabetes.
Collectively, these findings demonstrate that alterations in platelet and endothelial function that favor thrombosis occur early in the diabetic state and may contribute to microvascular disease. There are several ongoing studies of antiplatelet agents in diabetic vascular disease that will provide clinical evidence bearing on the major postulate. Until these and other studies are completed, the platelet-endothelial story remains an attractive hypothesis in the genesis of diabetic microvascular disease.
Studies on the Pathophysiology of Diabetic Retinopathy: The Blood-Retinal Barrier in Diabetes
Authors: Cunha-Vaz José G 
Published: September 2013

A review of the pathologic picture of diabetic retinopathy shows that available clinical methods of examination demonstrate the alteration of the blood-retinal barrier (leakage), microaneurysms, capillary closure, preferential channels, preretinal neovascularization and gross extravascular lesions. All of these changes may be shown by fluorescein angiography. The value of this method, however, is fundamentally related to the morphologic demonstration of these lesions and not their quantification. Quantitative evaluation of retinal involvement in diabetes is needed in order to delineate more clearly its natural history, criteria for prognosis, and effect of treatment.
Vitreous fluorophotometry, a quantitative and sensitive method of evaluating the permeability of the blood-retinal barrier, has opened new perspectives for the evaluation of retinal involvement in diabetes. Vitreous fluorophotometry has shown that a disturbance of the blood-retinal barrier, possibly functional, appears in diabetic eyes before any lesion is clinically visible in the fundus, and that there is a close correlation between the severity of the vascular lesions and higher vitreous fluorophotometry readings. Recent studies also indicate an interesting correlation with metabolic control, particularly, glycosylated hemoglobin levels and insulin treatment.
Finally, on the basis of these findings a working hypothesis for the pathogenesis of diabetic retinopathy is presented.