bluuebunny/crossref_metadata_2025_split huggingface dataset:
Membrane Structural/Functional Properties of Adipocytes from Normal and Streptozotocin-diabetic Rats
Authors: Sauerheber Richard D , Kuhn Chris E , Hyslop Paul A 
Published: September 2013

The uptake of 2-deoxy-D-[-14C]-glucose, in the presence and absence of insulin, was measured in adipocytes from normal and streptozotocin-diabetic animals, over a wide temperature range (25–45°C). Optimum temperatures for uptake in the presence of maximally stimulating insulin concentrations occurred near physiologic temperatures. Both high and low temperatures lead to progressive inhibition of insulin-sensitive uptake, whereas basal uptake was only marginally affected. It is possible that the apparent “resistance” to insulin action at high (febrile) temperatures may have pathologic significance.
The magnitude of 2-deoxy-D-glucose uptake at all temperatures in the diabetic adipocytes was much reduced, both in the presence and absence of insulin, on a per cell basis, compared with cells from age-matched control animals. However, the fold stimulation of uptake caused by insulin at 35°C is comparable in both normal and diabetic adipocytes (approximately 2–3-fold).
Photomicrographs of adipocytes were used to estimate the cell diameters of the average normal (50 μm) and diabetic (37 μm) cells. The diabetic adipocytes are not “resistant” to insulin action in terms of 2-deoxy-D-glucose uptake since the basal and insulin-stimulated uptake magnitudes per μm2 membrane surface area are identical in both normal and diabetic cells (within experimental error). It is possible that the decreased diabetic cell size reflects the reduced antilipolytic effects of chronic hypoinsulinemia rather than any inherent resistance to insulin action in the cell itself.
The basal and insulin-stimulated overall removal of glucose from the incubation medium by adipocytes, isolated from the normal and streptozotocin-treated rats, was also measured. Both the overall glucose uptake magnitude per μm2 membrane surface area and the fold increase in glucose uptake due to insulin were identical between cells obtained from the two groups of animals. Any intracellular metabolic resistance to the effects of exogenous insulin that may be present in cells from the diabetic rats does not appear to grossly interfere with the accelerated net utilization of glucose induced by exposure to the hormone in vitro.
Purified plasma membranes from normal and diabetic adipocytes were examined in spin label studies. No differences in the flexibility of either the 5-nitroxide stearate or the cholestane (cholesterol-like) spin labels were noted between the two animal groups at any temperature between 15 and 40°C Although the diabetic membrane may well exhibit differing structural/functional properties compared with controls, our data do not support the concept that gross alterations in the lipid structure of the membrane occur in this hyperglycemie condition.
Calmodulin and Cyclic AMP: Possible Different Sites of Action of These Two Regulatory Agents in Exocytotic Hormone Release
Authors: Steinberg Jay P , Leitner J Wayne , Draznin Boris , Sussman Karl E 
Published: September 2013

It may now be possible to identify certain intracellular events that impact specifically on secretion-granule fusion to the plasma membrane or on granule lysis. Secretion vesicles in isolated rat islets appear to translocate somatostatin (SRIF) receptors from the Golgi apparatus to the plasma membrane. We have proposed that secretion granule fusion to the plasma membrane can be determined by measuring recruitment of SRIF receptors to the surface membrane. Granule lysis can be assessed by measuring insulin release. To activate cyclic AMP (cAMP)-dependent pathways, we employed isobutylmethylxanthine (IBMX, 400 μM), glucagon (10 μM), and forskolin (20 μM), a diterpene activator of adenylate cyclase. These agents evoked rapid release of insulin (from 0.41 ± 0.02 to 1.88 ± 0.02; 0.41 ± 0.02 to 1.93 ± 0.08; and 0.41 ± 0.02 to 1.66 ± 0.03 μU/islet/ min, respectively, P &lt; 0.001). There was no concomitant recruitment of SRIF receptors. Somatostatin (10 μg/ml), which inhibits cAMP-stimulated protein phosphorylation, suppresses insulin release evoked by IBMX, glucagon, or forskolin (inhibition: 80, 75, or 82%, respectively). In contrast, trifluoperazine (10 μM), an inhibitor of calmodulin, did not suppress insulin release induced through cAMP-dependent pathways. Trifluoperazine suppresses glucose-induced insulin release and the recruitment of SRIF receptors to the surface membrane, suggesting the possible role of calmodulin in promoting secretion-granule fusion with the plasma membrane.
These data suggest that granule fusion to the plasma membrane may be a calmodulin-directed function. In contrast, the major site of action of CAMP in polypeptide hormone secretion may be in promoting lysis of secretion granules and associated hormone discharge.
Increased Insulin Responsiveness In Vivo and In Vitro Consequent to Induced Hyperinsulinemia in the Rat
Authors: Trimble E R , Weir G C , Gjinovci A , Assimacopoulos-Jeannet F , Benzi R , Renold A E 
Published: September 2013

The effect of constant, controlled hyperinsulinemia on in vivo and in vitro insulin responsiveness has been investigated in rats that have received insulin infusions through chronically implanted jugular vein catheters. Constant rates of insulin infusion during days 1–4 resulted in stable plasma insulin concentrations. The plasma glucoseinitially fell from 122 ± 3 to 53 ± 4 mg/dl. While the infusion rate was maintained constant,the plasma glucose continued to fall over the subsequent days so that on day 4 the plasma glucose, 40 ± 2 mg/dl, was significantly lower than that in the same animals on day 1 (P &lt; 0.02). Subsequently, the rate of insulin infusion was decreased to maintain the plasma glucose level in the 35—40 mg/dl range. Plasma catecholamine levels were high in insulin-infused rats. On the eighth day an in vivo insulin tolerance test (0.5 U/kg) was performed. Insulin-infused rats responded with a hypoglycemia that was both more pronounced and longer sustained than in salineinfused controls.
Insulin responsiveness in vitro has been measured in isolated adipocytes. Adipocytes from epididymal fat pads were of similar size in the two groups of animals. Glucose uptake by adipocytes from insulin-infused rats was similar to that of controls under basal (zero insulin) conditions, but showed an increase in the maximum response to insulin. Glucose incorporation into total lipid and fatty acid was greater in adipocytes from insulin-infused rats than in controls under both basal (zero insulin) and insulin-stimulated conditions. Activities of the lipogenic enzymes acetyl CoA carboxylase and fatty acid synthetase were markedly increased in epididymal fat pads of insulin-infused rats.
Thus, insulin infusion for a period of 8 days did notresult in reduced insulin action in vivo; on the contrary, an apparent increase in the hypoglycemic effect of insulin was observed. In vitro, the maximum effect of insulin on glucose uptake and lipogenesis in the isolated adipocyte was markedly increased after in vivo insulin infusion.
Abnormal Glucose Regulation of Insulin Secretion in Models of Reduced B-Cell Mass
Authors: Leahy J L , Bonner-Weir S , Weir G C 
Published: September 2013

The influence of glucose on nonglucose-stimulated in sulin secretion was examined in two animal models with reduced B-cell mass: rats treated with streptozotocin as neonates (SZ) and rats with a partial pancreatectomy (Px). The effects of arginine and IBMX upon insulin secretion were studied at varying glucose con centrations using the in vitro, isolated, perfused pan creas.
In normal rats, as expected, 16.7 mM glucose caused a biphasic insulin release and arginine-stimulated in sulin secretion was markedly potentiated by an in crease in background glucose concentration. In the SZ model, 16.7 mM glucose caused a minimal insulin re sponse. However, arginine stimulated insulin release at 2.8 mM glucose as well as at higher glucose concen trations. A similar alteration in the glucose regulation of insulin secretion was shown with another secret agogue, IBMX, even though responses to this agent in the SZ rats exceeded those of the controls at both high- and low-background glucose concentrations. The less diabetic, Px model showed partial preservation of the glucose regulation of the B-cell response to arginine.
Thus, a reduction in B-cell mass leads not only to a toss of glucose-stimulated insulin secretion but also to impaired glucose regulation of nonglucose-stimulated insulin secretion.
Evidence for Separate Handling In Vivo of Different Regions of the Insulin Molecule Using A14- and B1-labeled Insulin Tracers
Authors: Cockram Clive S , Jones Richard H , Boroujerdi Massoud A , Sönksen Peter H 
Published: September 2013

To compare the metabolic characteristics and degradation of insulin tracers labeled unselectively, selectively at the A14 position (A14-monoiodoinsulin), and selectively at the B1 position (B1-monoiodoinsulin), we have followed the time course of disappearance of intact (immunoprecipitable [IP] and trichloroacetic acid [TCA] precipitable) iodoinsulin after bolus injection into greyhounds. We have used noncompartmental analysis to determine metabolic clearance rate (MCR) and apparent distribution space (DS). We have also measured the appearance of non-IP- and non-TCA-precipitable fragments, and have developed a mathematical model using compartmental analysis to explain the observed differences.
B1-Monoiodoinsulin has a significantly higher MCR (16.3 ml/min/kg) than both A14-monoiodoinsulin (10.6 ml/min/kg) and unfractionated tracers (7.6 ml/min/kg) as determined by immunoprecipitation, and reaches the values observed for native insulin in greyhounds. MCR values obtained by TCA precipitation are approximately one-half of those obtained by IP for all 3 tracers. The concentration of non-IP fragments is significantly lower with B1-monoiodoinsulin than with the other tracers. Compartmental analysis suggests this to be due to greater intracellular retention of the B1 moiety during the experimental period.
We conclude that: (1) by the criterion of MCR, B1-monoiodoinsulin seems to behave more like native insulin than other preparations tested; (2) the reduced MCR of A14-monoiodoinsulin raises doubts about its validity as a tracer for insulin; (3) a high-molecular-weight product of insulin degradation, which includes both the B1 and the A14–A19 regions of the molecule, is released into the circulation; and (4) smaller fragments containing A14–A19 reappear in the circulation more rapidly than fragments containing B1. Thus, the use of specifically labeled insulin tracers allows investigation of the mechanisms of intracellular processing in Vivo.
The Effects of Biosynthetic Human Proinsulin on Carbohydrate Metabolism
Authors: Revers R R , Henry R , Schmeiser L , Kolterman O , Cohen R , Bergenstal R , Polonsky K , Jaspan J , Rubenstein A , Frank B , Galloway J , Olefsky J M 
Published: September 2013

Large quantities of biosynthetic human proinsulin have recently become available through recombinant DNA technology. Since the in vivo effects of human proinsulin have not been studied in man, we compared the dose-response relationship for stimulation of glucose disposal and suppression of hepatic glucose output by proinsulin and insulin. Ten normal subjects were studied using the euglycemic glucose clamp technique. The human proinsulin and insulin infusion rates were chosen to achieve steady-state proinsulin levels 10-fold higher than insulin levels on a molar basis, based on previous observations that porcine proinsulin has ∼10% the potency of insulin. Proinsulin infusion rates of 2.75, 7.5, 22.5, and 45 μg/m2/min were compared with insulin infusion rates of 0.63,1.67, 5, and 10 μg/ m2/min. Primed, continuous infusions of insulin yielded steady-state levels within 25 min, whereas proinsulin levels did not reach a steady state for 120–180 min. The metabolic clearance rate of insulin was 11–12 ml/kg/min at the lower infusion rates but fell to 8.4 ml/kg/min at the highest infusion rate. The metabolic clearance rate of proinsulin was 3.0–3.5 ml/kg/ min at all infusion rates. Dose-response analysis demonstrated that proinsulin-mediated glucose disposal was ∼8% that of insulin. In contrast, proinsulin-mediated suppression of hepatic glucose output was ∼12% that seen with insulin.
We conclude that: (1) primed, continuous infusions of proinsulin and insulin have considerably different kinetics; (2) the metabolic clearance rate of proinsulin is only −28% that of insulin, but the processes responsible for removal of insulin from the circulation are more saturable than those responsible for removal of proinsulin; and (3) proinsulin appears to exert a greater effect on hepatic than on peripheral tissues.
Binding of Insulin to Its Receptor Impairs Recognition by Monoclonal Anti-insulin Antibodies
Authors: Taylor Simeon I , Schroer Joyce A , Marcus-Samuels Bernice , McElduff Aidan , Bender Timothy P 
Published: September 2013

The interaction between insulin and its receptor was investigated using both monoclonal and polyclonal anti-insulin antibodies. After covalent cross-linking of 125I-insulin to the insulin receptor on cultured human lymphocytes (IM-9 cells) using disuccinimidyl su berate, we inquired whether the insulin-receptor complex could be immunoprecipitated with anti-insulin antibodies. While a polyclonal guinea pig anti-insulin anti-serum succeeded in immunoprecipitating receptor-bound 125I-insulin, binding to the receptor decreased the avidity of the antiserum for the insulin moiety by a factor of approximately 1000-fold. Sixteen distinct monoclonal murine anti-insulin antibodies were employed to immunoprecipitate receptor-bound 125I-insulin. Of these 16 monoclonal antibodies, only one (antibody 5.9F4) could be shown to recognize receptor-bound 125I-insulin. Moreover, even with antibody 5.9F4, binding of 125I-insulin to its receptor reduced the affinity of the antibody by a factor of 10- to 100-fold.
These data strongly suggest that, when insulin binds to its receptor, the majority of the insulin molecule is unavailable for binding by anti-insulin antibodies. It seems likely that the hormone binding site on the receptor may be very large, thereby allowing for sequestration of the majority of the insulin molecule with relatively little of the hormone remaining exposed.
Insulin-mediated Glucose Uptake in Nondialyzed and Dialyzed Uremic Insulin-dependent Diabetic Subjects
Authors: Schmitz Ole 
Published: September 2013

A three-step euglycemic insulin clamp was performed in six matched groups: nine healthy subjects, 10 insulin-dependent diabetic (IDD) subjects with normal kidney function, 10 nondiabetic uremic subjects, six nondialyzed uremic IDD subjects, seven uremic IDD subjects on chronic hemodialysis (HD), and six uremic IDD subjects on chronic ambulatory peritoneal dialysis (CAPD). Insulin was infused sequentially at rates of 0.5 (step 1), 2.0 (step 2), and 4.0 (step 3) mU · kg−1 · min−1. Each dose was given for 120 min; however, in theIDD subjects with fasting hyperglycemia, step 1 of the clamp was slightly extended. Average serumfree insulin levels at steady state ranged from 22 to 342 μU/ml and were comparable in all groups. Step 3 glucose infusion rate (GIR), the last 30 min of the infusion period, was extremely suppressed in nondialyzed uremic IDD subjects, amounting to 53% of that in healthy subjects (7.7 ± 0.7 versus 14.4 ± 0.9 mg · kg−1 · min−1 P &lt; 0.001) indicating severe insulin resistance in peripheral tissues. As expected, step 3 glucose disposal was also reduced in IDD subjects with normal kidney function (12.4 ± 0.6 mg · kg−1 · min−1) and nondiabetic uremic subjects (9.2 ± 0.6 mg · kg−1 · min−1) as compared with healthy subjects (P = 0.06 and P &lt; 0.001, respectively). The pronounced impairment of insulin responsiveness in nondialyzed uremic IDD subjects was almost equal to the sum of the defects in nondiabetic uremic and IDD subjects with normal kidney function. Step 2 of the sequential insulin infusion resulted in differences in GIR between the above-mentioned groups that were analogous to those encountered at the highest insulin infusion rate. During step 1 the average steady-state GIR, reflecting the sum of suppression of glucose production and stimulation of glucose utilization, was more than twofold higher in healthy subjects than in the nondialyzed patient groups. In contrast, the insulin action on Iipoiysis and ketogenesis as assessedby changes in serum NEFA and blood 3-hydroxybutyrate was normal in the patient groups. In the patients treated by HD and CAPD insulin responsiveness (step 3 GIR) was enhanced or tended to be so compared with nondialyzed uremic IDD individuals (9.5 ± 0.7 and 12.2 ± 0.7 mg kg−1 min−1 P = 0.07 and P &lt; 0.001, respectively). Furthermore, GIR at all three steps was significantly higher in the CAPD group than in the HD group (P = 0.08, P &lt; 0.001, and P &lt; 0.03). No difference in degree of azotemia or glycemic and metabolic control wasobserved between the dialyzed groups.
In conclusion, nondialyzed uremic IDD individuals exhibit extreme insulin resistance in peripheral tissue that is probably the result of several intracellular defects. In uremic IDD subjectstreated with CAPD, the insulin-mediated glucose uptake is closer to normal than in IDD subjects on HD. Potentially lower peripheral insulinemia in diabetic CAPD patients having insulin administered intraperitoneally may contribute to this difference.
Modulation of Adipose Lipoprotein Lipase by Thyroid Hormone and Diabetes: The Significance of the Low T3 State
Authors: Gavin Laurence A , McMahon Francis , Moeller Marie 
Published: September 2013

The present study was performed to assess the potential relationship between the low T3 syndrome and hypothyroidism. Comparative studies were performed on the relative effects of diabetes and insulin on heparinreleasable adipose lipoprotein lipase (LPL) in the intact and hypothyroid rat. Hypothyroidism for 10 days (Tx) significantly increased adipose LPL activity (5.8 ± 0.2 μeq/g/h) compared with the activity (3.6 ± 0.4 μeq/g/h) in the normal group. Diabetes for 72 h (streptozocin, STZ, 10 mg/100 g body wt, i.p.) significantly reduced (P &lt; 0.005) adipose LPL activity in the Tx model. However, despite the suppressant effect of diabetes (43 ± 11%), the enzyme activity remained equivalent to the normal group. Insulin stimulated adipose LPL in the Tx-diabetic group. The enzyme demonstrated a synergistic response to insulin and hypothyroidism. Subsequent studies were performed in the intact diabetic rat, a low T3 state. Adipose LPL activity was reduced to a similar degree by diabetes (79 ± 2%) irrespective of the serum T3 concentration. Furthermore, the magnitude of the adipose LPL stimulation by insulin was not modulated by the endogenous serum T3. However, co-treatment of the diabetic group with T3 and insulin blunted the adipose LPL response to insulin. These various modulations in adipose LPL activity were associated with significant but opposite changes in serum triglyceride levels in both the hypothyroid and intact rat.
These studies demonstrate that hypothyroidism counteracts the suppressant effect of diabetes on heparin-releasable rat adipose LPL activity and magnifies the enzyme response to insulin. The synergistic effect of hypothyroidism and insulin on adipose LPL activity suggests that the enzyme responds through different mechanisms. In contrast, the low T3 state associated with diabetes did not influence the adipose LPL response to diabetes or insulin therapy. Thus, the low T3 state in the rat does not reflect hypothyroidism. The low T3 state may, however, have a permissive role as it facilitated the adipose LPL response to insulin in the diabetic rats. Therefore, T3 therapy is contraindicated under these condition.
The Effects of Variations in Percent of Naturally Occurring Complex and Simple Carbohydrates on Plasma Glucose and Insulin Response in Individuals with Non-insulin-dependent Diabetes Mellitus
Authors: Hollenbeck Clarie B , Coulston Ann M , Donner C Christopher , Williams Robin A , Reaven Gerald M 
Published: September 2013

In the present study, 12 patients with non-insulin-dependent diabetes mellitus (NIDDM) consumed eucaloric, mixed food diets on three consecutive days. Diets provided 50% of the calories as carbohydrate, 35% as fat, and 15% as protein. The percent of carbohydrate fed as complex (starches) and simple (monoand disaccharides) varied among the 3 days. On day 1, the diet contained 80% of the carbohydrate as complex and 20% as simple (80/20); another contained 50% complex and 50% simple (50/50); and the final diet contained 20% of the carbohydrate as complex and 80% as simple (20/80). All simple carbohydrates represent naturally occurring sugars in fruits, vegetables, and dairy products. No refined sugars were added to any of the diets. The three experimental diets were randomly assigned using a 3 × 3 Latin square design.
Blood was obtained hourly from 0800 to 1700 h for day-long glucose and insulin concentrations, and 24-h urine collections were made for the measurement of urine glucose. Mean (± SEM) day-long glucose concentrations were significantly greater for the 80/20 diet (2245 ± 199 mg/dl · h, P &lt; 0.05) than for either the 50/ 50 (2030 ± 157 mg/dl · h) or the 20/80 diets (2008 ± 160 mg/dl · h). No significant differences were noted between the 50/50 and the 20/80 diets. In contrast, day-long insulin concentrations were not significantly different with 401 ± 62, 370 ± 50, and 369 ± 60 μU/ ml · h on the 80/20, 50/50, and 20/80 diets, respectively. Twenty-four-hour urinary glucose excretion paralleled plasma glucose concentrations. Significant differences were noted when the 80/20 diet (25.1 ± 4.5 g/ 24 h, P &lt; 0.05) was compared with the 20/80 diet (9.7 ± 3.3 g/24 h). Substantial quantitative differences also existed between the 80/20 and 50/50 (12.2 ± 4.5 g7sol;24 h), but these differences did not reach statistical significance.
The results of the present study support the hypothesis that variations in relative proportions of naturally occurring, complex and simple dietary carbohydrate will have no deleterious effect on glycemia in patients with NIDDM. Thus, there seems to be no apparent reason why patients with NIDDM should avoid foods that are high in naturally occurring, simple carbohydrate.
Antepartum Fetal Surveillance in Gestational Diabetes Mellitus
Authors: Landon Mark B , Gabbe Steven G 
Published: September 2013

Pregnancy in patients with gestational diabetes mellitus (GDM) is associated with increased perinatal morbidity. Whether the perinatal mortality rate, particularly the fetal death rate, is greater in these patients remains controversial. The present study was undertaken to review the role of antepartum fetal monitoring in 69 patients with GDM controlled by diet only (class A) and 28 women requiring insulin therapy (class AB). Hypertension complicated 21.6% of these pregnancies.
Antepartum fetal surveillance included outpatient nonstress testing, urinary estriol assays, maternal assessment of fetal activity, and clinical estimation of fetal weight. All insulin-requiring patients as well as fourteen class A patients with identifiable risk factors underwent testing. No perinatal deaths occurred. Only six patients required intervention for suspected fetal jeopardy and four of these women had hypertension. Macrosomia was correctly identified in only 6 of 16 infants weighing 4000 g or more.
This study suggests that, in GDM, an outpatient program of fetal testing, using primarily the nonstress test and maternal assessment of fetal activity, can be employed in patients requiring insulin as well as class A patients with identifiable risk factors. This protocol resulted in a low rate of unnecessary intervention and good perinatal outcome. The risks for abnormal antepartum testing results appear increased in GDM with hypertension and prolonged pregnancy.