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At least 19 recordsLinked to original sources

PubMedDate not supplied

Serum insulin, insulin antibodies and insulin requirement in the first period of insulin treatment in non-insulin resistant diabetics.

Twelve insulin-sensitive diabetics were studied for 200 days after the initiation of mixed beef-pork NPH insulin. Normalization of the fasting blood glucose was not accompanied by any elevation in the pre-treatment fasting immunoreactive insulin level. Insulin antibodies appeared in 2 patients on the second week of insulin treatment, in 6 others within 87 days. In 4 patients no antibodies were found 200 days after the start of insulin. The appearance of antibodies was accompanied in two patients by a decrease in insulin requirement, in others there was no change. When antibodies were present, the total maximum insulin binding capacity was 4 to 12 U/l, but the total insulin constituted only 3 to 36% of the binding capacity. Insulin wastage caused by the destruction of the immune complexes was calculated to be 0.35 to 5.6 U/die only, and this explains the negligible effect of insulin antibodies on insulin requirement in non-resistant patients.

Adolescent↗

PubMedDate not supplied

Attempts to prepare 'insulin-free plasma' from human subjects: effects of serial dilution and insulin recovery studies on immunoreactive insulin activity of partially insulin-free plasma.

The reason for attempts to prepare insulin-free plasma from human plasma is discussed. Binding agent, employed to prepare insulin-free plasma, had a capacity to bind 40% of insulin in the system. Insulin recovery from the filtrate of human standard insulin-binding agent reaction was 60%. Human plasma incubated with binding agent gave a filtrate--partially insulin-free plasma (PIFP)--which contained significantly higher amounts of insulin compared to calculated values. Insulin in PIFP was not augmented by serial dilution. Human standard insulin added to PIFP was recovered in full and the mixture was not dilution augmentable. Incubation of human plasma--human standard insulin (106 microunits/ml) mixture with binding agent gave a PIFP which had 60% of total insulin in the mixture. Dialysis did not alter the immunoreactive insulin activity of plasma. Dialysed samples showed augmentation of insulin activity on serial dilution. These observations strongly suggest the presence of a high molecular-weight, insulin-like inhibitory component in human plasma.

Antigens↗

PubMed1992

Correlation of insulin receptor level with both insulin action and breakdown of a potential insulin mediator precursor; studies in CHO cell-lines transfected with insulin receptor cDNA.

A phosphatidylinositol-glycan (PI-glycan) has been described previously that may serve as the precursor for a mediator of some of insulins actions. The present study further addresses the potential relevance of this compound by correlating its breakdown with other insulin actions in Chinese hamster ovary (CHO) cells which express different levels of insulin receptor. Comparisons were drawn between parent CHO cells expressing 3 x 10(3) receptors/cells and two cell-lines transfected with human insulin receptor cDNA, that expressed 600 (CHO.TH) and 300 (CHO.T) times the parent receptor level. A PI-glycan was isolated from all cells that incorporated [3H]glucosamine, [3H]galactose and [3H]inositol and was rapidly turned over upon insulin stimulation. Maximal turnover by insulin of approx. 20% was achieved in each cell line consistent with the fibroblastic nature of these cells. The effect of increased insulin receptor expression was to increase the sensitivity of the PI-glycan response to insulin. Increasing receptor number from 3 x 10(3) to 0.88 x 10(6) also increased the sensitivity of response of other insulin actions measured in this study, namely activation of pyruvate dehydrogenase (PDH), glucose utilization and transport. Thus turnover of the PI-glycan is linked closely to both metabolic actions of insulin and to cell surface insulin receptor expression further supporting its potential role in insulin action.

Animals↗

PubMed1978

Change of insulin dosage, circulating free and bound insulin and insulin antibodies on transferring diabetics from conventional to highly purified porcine insulin.

Fifty-eight patients on long term conventional mainly bovine insulins have been transferred to highly purified porcine insulin preparations. There was an overall reduction of 22% in daily insulin dosage and improved diabetic control as shown by decreased blood glucose concentration. Increased concentrations of serum free insulin and falls in serum bound insulin levels were also found. There were reductions in the serum binding capacities and affinity constants on changeover from conventional to highly purified insulin due to a combination of the effects of differential conventional/purified porcine binding and the substitution of a low antigenicity insulin. However, 12 of the patients receiving higher doses of insulin experienced marked hypoglycaemic reactions immediately on insulin changeover despite initial dosage reductions of 30% and prior to any changes in antibody characteristics.

Adolescent↗

PubMed1979

Insulin action in isolated fat cells. II. Effects of divalent cations on stimulation by insulin of protein synthesis, on inhibition of lipolysis by insulin, and on the binding of 125I-labelled insulin to isolated fat cells.

The effects of ommission of Ca2+ and Mg2+ from the incubation medium on three aspects of insulin action in isolated fat cells have been investigated. In the (Ca2+ + Mg2+)-free incubation medium incorporation of L-[14C]leucine into fat cell protein was reduced in the absence of insulin. Insulin stimulated L-[14C]leucine incorporation only in the presence of added CaCl2 or MgCl2. Incubation of the cells in the (Ca2+ + Mg2+)-free medium reduced but did not abolish the ability of adrenaline to stimulate lipolysis or the ability of insulin to inhibit the adrenaline-stimulated lipolysis. Specific binding of 125I-labelled insulin to the fat cells was reduced in the absence of Ca2+ and Mg2+ but was not abolished, even in the presence of EDTA. Ca2+ was routinely the most effective divalent cation in supporting these aspects of insulin action, but similar responses were obtained with Mg2+, Sr2+ and Ba2+. Since insulin still binds to the cells under conditions in which some of the cellular effects of the hormone are abolished, it is suggested that divalent cations may have a role, either direct or indirect, in the processes linking the insulin-insulin receptor complex to certain effector systems in the cells. It is tentatively suggested that this action occurs at the level of the fat cell plasma membrane.

Adipose Tissue↗

PubMed1992

Insulin receptor gene expression during development: developmental regulation of insulin receptor mRNA abundance in embryonic rat liver and yolk sac, developmental regulation of insulin receptor gene splicing, and comparison to abundance of insulin-like growth factor 1 receptor mRNA.

Insulin gene expression has been demonstrated in nonpancreatic tissues early in development, suggesting that this hormone might have actions significant for the differentiating embryo. Because such actions imply ligand-receptor binding, we quantified mRNAs encoding the two known forms of insulin receptor in rat liver and yolk sac, two endodermally derived tissues shown to express insulin genes, between gestation days (E) 13 and E21 (mid-organogenesis to parturition). Because of its presumed importance for fetal growth, we estimated the abundance of mRNA encoding insulin-like growth factor 1 (IGF 1) receptor in the same samples for comparison. The abundance of insulin receptor mRNA exceeded that for IGF 1 receptor mRNA in liver and yolk sac at all times studied. This difference was greater in liver, where insulin receptor mRNAs were three to more than 50 times more abundant than IGF 1 receptor mRNA on gestation days E13-E16, times which antedate the development of significant hepatic metabolic actions of insulin. The marked abundance of mRNAs encoding insulin receptors is consistent with the hypothesis that insulin has significant actions in specific tissues during the organogenic period.

Animals↗

PubMed1978

The relationship between circulating free and bound insulin, insulin antibodies, insulin dosage and diabetic control in insulin treated diabetics.

Free and bound insulin concentrations, blood glucose and anti-insulin antibody binding characteristics have been determined in 100 insulin treated diabetics; medium serum free insulin was 11 mU/l when fasting and rose to 30 mU/l after the mid-day meal. Significant correlation between blood glucose and serum free (but not bound) insulin was found. No relationship between insulin antibodies and daily insulin dose or diabetic control were found, nor a relationship between free insulin and antibody characteristics.

Adolescent↗

PubMed1977

Structure and activity of insulin, XV[1-5]. Further evidence for the importance of arginine residue B22 in the activity of insulin. Semisyntheses of despentapeptide-(B23 - 30)-insulins varied in B22 using desnonapeptide-(B22 - 30)-insulin and tetrapeptides.

Insulin hexamethyl ester was digested by trypsin. The resulting desoctapeptide-(B23 - 30)-insulin pentamethyl ester was purified. This compound was digested by carboxypeptidase B to remove the arginine residue B22 at the end of the B chain. Then the N-terminal amino groups of the remaining desnonapeptide-(B22 - 30)-insulin pentamethyl ester were protected with the Boc residue. The free carboxyl group of the glutamic acid residue B21 of this product was coupled to the following synthetic tetrapeptide esters: Arg-Gly-Phe-Phe-OMe, Lys(Boc)-Gly-Phe-Phe-OMe, Orn(Boc)-Gly-Phe-Phe-OMe, Cit-Gly-Phe-Phe-OMe, Ala-Gly-Phe-Phe-OMe and Gly-Gly-Phe-Phe-OMe. The syntheses of these peptide esters are described. After removal of all protecting groups, despentapeptide-insulin (B22-Arg) and analogues of this product with variation in position B22 could be obtained. They were purified by column chromatography. The biological activities of these components were determined by the mouse fall test. In the case of despentapeptide insulin (C-terminus Arg-Gly-Phe-Phe), the activity rose to the expected value of 34%. The insulin variants with amino acid residues other than arginine in position B22 had much lower activities: with lysine 13%, with ornithine 12%, with citrulline 9%, with alanine 8% and with glycine 6%. Desnonapeptide-insulin by itself posses an activity of 3%. These results demonstrate once more the essential nature of arginine residue B22 for insulin activity.

Animals↗

PubMed1992

Insulin, glibenclamide or metformin treatment for non insulin dependent diabetes: heterogenous responses of standard measures of insulin action and insulin secretion before and after differing hypoglycaemic therapy.

Using carefully selected relatively non-obese non insulin dependent diabetic patients, we were not able to show differences in standard measures of insulin production or insulin action between patients treated with a long acting crystalline zinc insulin, with glibenclamide, or with metformin for a six week period. All three drugs were hypoglycaemic, but a fall in basal hepatic glucose output measured by the 3H3 glucose technique was only seen in those patients who had an initial fasting plasma glucose above 12.0 mmol/l, irrespective of treatment.

Blood Glucose↗

PubMed1979

Effect of cytochalasin B and D on groups of insulin receptors and on insulin action in rat adipocytes. Possible evidence for a structural relationship of the insulin receptor to the glucose transport system.

The possible physiological importance of the groups of insulin receptors on rat adipocytes and the relationship of these groups to insulin action were investigated. The effect of cytochalasin B and D on biological actions of insulin was measured and compared with the effect of these agents on the ultrastructural distribution of groups of insulin receptors. Cytochalasin B had no effect on epinephrine-stimulated lipolysis, insulin inhibition of epinephrine-stimulated lipolysis, or insulin stimulation of protein synthesis. Cytochalasin B, over a concentration range of 50 nM to 5 muM, progressively inhibited the basal glucose transport system, as measured by glucose oxidation, 2-deoxyglucose transport, and 3-O-methylglucose transport. Insulin was capable of fully stimulating remaining basal transport at submaximal concentrations of cytochalasin B. Insulin pretreatment of adipocytes partially protected the glucose transport system from inhibition by cytochalasin B. Cytochalasin B markedly altered the distribution pattern of insulin receptors, which caused an increase in the number of single receptor molecules by decreasing the number of larger groups. A significant correlation (r = 0.964; P < 0.001) was found between the percent increase in single receptors and the percent decrease in glucose transport. Ferritin-insulin pretreatment of adipocytes prevented disruption of the groups of insulin receptors by cytochalasin B. Cytochalasin D had no effect on the biological actions of insulin or on the groups of insulin receptors. These data suggest that the ability of insulin to affect adipocyte metabolism is independent of the hormone occupying adjacent, grouped receptor sites. The marked contrast in effects of cytochalasin B and D on groups of insulin receptors and glucose transport suggests that the microfilament system is not involved in insulin action or in holding the groups of insulin receptors together, as both agents are known disrupters of microfilaments and inhibitors of actin gelation. The correlation between the effects of cytochalasin B on insulin receptor distribution and glucose transport leads to the speculation that the glycoprotein molecules containing the insulin receptor are functionally linked with the glucose transport system.

Adipose Tissue↗

PubMed1992

Insulin can rapidly increase cell surface insulin binding capacity in rat adipocytes. A novel mechanism related to insulin sensitivity.

To elucidate the acute effect of insulin on its receptor, rat adipocytes were preincubated with insulin, washed with KCN to inhibit receptor cycling, and 125I-labeled insulin binding was measured. Preincubating cells from young insulin-sensitive rats with insulin increased cell surface binding up to approximately fourfold without changing apparent receptor affinity. This effect was rapid (t1/2 less than 5 min) and had a similar dose-response relationship as the effect on glucose transport. It was also energy dependent because preincubation with KCN completely abolished the effect of subsequent insulin exposure. The increased binding capacity was not recovered after cell solubilization or in partially purified receptors or isolated plasma membranes. Cells pretreated with insulin were less sensitive to the ability of trypsin to remove cell surface receptors, suggesting a conformational change of the receptors. This was also supported by the finding that the polyclonal binding in insulin-treated but not in control cells. Vanadate mimicked the effect of insulin to increase insulin binding, whereas concanavalin A, vasopressin, phorbol esters, or the adenosine analogue phenyl isopropyl adenosine was without effect. Insulin-resistant adipocytes from obese rats displayed no increase in cell surface binding after insulin treatment, despite normal tyrosine kinase activity in response to insulin. Thus, both insulin and vanadate elicit a rapid effect to markedly increase the number of cell surface insulin binding sites in intact rat adipocytes. This appears to occur independently of protein kinase C and the inhibitory GTP binding protein (Gi). Furthermore, the effect of insulin could not be demonstrated in insulin-resistant cells, suggesting that this mechanism may be of importance for the regulation of insulin sensitivity.

3-O-Methylglucose↗

PubMed1977

[Clinical effects of monocomponent insulin and commercial insulin preparations on insulin requiring diabetics (author's transl)].

Diurnal variation of blood sugar, C-peptide immunoreactivity (CPR), free insulin and total insulin were measured in 10 insulin requiring diabetics after obtaining adequate control of diabetes with commercial lente insulin treatment. Following these tests, insulin treatment were changed to monocomponent insulin (MC-insulin) from commercial lente insulin treatment in all subjects and the same tests were performed at 7th day of MC-insulin treatment. Diurnal variations of blood sugar in both groups were not changed significantly. Also changes in CPR of both groups were nearly same magnitude and endogenous insulin secretion in these insulin treated diabetics were suggested except a case of juvenile diabetic subject. However personal variation were great in diabetics with high antibody titer, diurnal variations of total extractable insulin in both groups were quite comparable. And mean diurnal changes in free insulin were resemble to that of CPR. All of these data suggested that clinical effects of MC-insulin and commercial insulin treatment on insulin requiring diabetics were comparable except insulin antibody or proinsulinspecific antibody production.

Adult↗

PubMed1992

Vanadate increases cell surface insulin binding and improves insulin sensitivity in both normal and insulin-resistant rat adipocytes.

The aim of this study was to elucidate the acute effects of vanadate on cell surface insulin binding and insulin sensitivity in rat adipocytes. The cells were preincubated at 37 degrees for 20 min followed by energy depletion with potassium cyanide, extensive washing and 125I-insulin binding. The presence of vanadate or insulin during the preincubation period dose-dependently enhanced 125I-insulin binding to normal adipocytes (maximally 4-5-fold) through an increased number of binding sites without any change in receptor affinity. Submaximal concentrations of vanadate added together with insulin enhanced the cellular sensitivity to the effect of insulin to stimulate 3-O-methylglucose transport. Vanadate, but not insulin, was also capable of increasing insulin binding as well as insulin sensitivity in insulin-resistant cells (treatment with N6-monobutyryl cAMP or amiloride and adipocytes from obese, aging rats). There was a correlation between the effect of vanadate to augment insulin binding and its ability to enhance cellular insulin sensitivity. Thus, the data suggest that short-term vanadate treatment improves insulin sensitivity through enhanced receptor binding and that this occurs in both normal and insulin-resistant cells.

3-O-Methylglucose↗

PubMed1992

Insulin secretion, insulin sensitivity and hepatic insulin extraction in primary hyperparathyroidism before and after surgery.

OBJECTIVE: Primary hyperparathyroidism (pHPT) is associated with hypertension, hyperinsulinaemia, and insulin resistance. The present study investigated the causes of these metabolic disturbances by quantifying insulin sensitivity and glucose effectiveness, and by assessing the time course of beta-cell insulin secretion and hepatic insulin extraction, during a dynamic condition such as after an intravenous glucose load. In addition, we evaluated the possible link between metabolic disorders and high blood pressure. SUBJECTS: We studied 16 patients with pHPT, before and 12 weeks after parathyroidectomy; eight of these patients were re-evaluated one year after surgery. The control group consisted of 18 healthy volunteers. DESIGN AND MEASUREMENTS: All subjects underwent an oral and a frequently sampled intravenous glucose tolerance test. The data from the intravenous glucose tolerance test were analysed by means of the minimal model technique which yields relevant parameters to comprehend the metabolic status of the single individual. RESULTS: The glucose intolerance condition was characterized by a severely impaired insulin sensitivity in pHPT (3.2 +/- 0.5 vs 9.5 +/- 1.5 x 10(4)/min/(microU/ml) of control subjects; P < 0.001), as well as by a reduced glucose effectiveness, (0.02 +/- 0.002 vs 0.03 +/- 0.003/min of control subjects; P < 0.04). Total insulin secretion during the 4 hours of the test was almost twofold elevated in comparison to the control subjects (32795 +/- 4769 vs 16864 +/- 1850 pM, P < 0.004) and its basal component significantly correlated with the high blood pressure. Hepatic extraction of insulin was significantly increased in pHPT (85 +/- 2 vs 76 +/- 2%, P < 0.03), possibly as a compensatory mechanism of hypersecretion, which however did not prevent peripheral hyperinsulinaemia in pHPT. Patients with pHPT were divided into two subgroups with normal and impaired glucose tolerance. The patients with impaired glucose tolerance had a significant reduction of first phase insulin response, although their basal and stimulated insulin levels were higher. Tissue insulin sensitivity and glucose effectiveness did not significantly differ between the two subgroups. After surgery, all the biochemical parameters (former hypercalcaemia, hypophosphataemia, elevated parathormone levels) were normalized, insulin sensitivity significantly improved (6 +/- 1 x 10(4)/min/(microU/ml), P < 0.001), whereas glucose effectiveness remained completely unchanged. Basal and stimulated insulin responses were insignificantly lowered after surgery, and hepatic extraction did not change either. CONCLUSIONS: Patients with pHPT exhibited decreased insulin sensitivity and insulin hypersecretion. The latter is only partially ameliorated by increased hepatic insulin extraction. After surgery, although the biochemical abnormalities were fully reversible, the metabolic changes improved only partially.

C-Peptide↗

PubMedDate not supplied

[Insulin autoantibodies and insulin-induced antibodies in children with insulin-dependent diabetes].

AIM OF THE STUDY: The aim was to study the time course of development of insulin antibodies during the first months of treatment in diabetic children, under human insulin therapy, and to see whether the presence of insulin autoantibodies influenced the subsequent binding to insulin. METHODS: Anti-insulin antibodies were measured using a radio-binding assay in 16 diabetic children, aged 4-13 years, before the first insulin injection and at regular intervals until the 9th month of treatment. RESULTS: Insulin autoantibodies were detected in 11 out of the 16 children at the time of diagnosis. Binding to insulin increased significantly after one month of treatment in these children, and after 2 months in the children with no insulin autoantibodies at diagnosis. After 2 months insulin therapy, all the children demonstrated antibodies against insulin. Insulin binding at 9 months was not correlated to the baseline values. Anti-insulin antibodies develop rapidly and frequently under human insulin, and are not influenced by the presence of insulin autoantibodies.

Adolescent↗

PubMed1992

Metformin ameliorates extreme insulin resistance in a patient with anti-insulin receptor antibodies: description of insulin receptor and postreceptor effects in vivo and in vitro.

The effect of metformin on insulin binding and insulin action in the presence of anti-insulin receptor antibodies was investigated in a case of type B extreme insulin resistance. Oral administration of metformin (1500 mg/d) for 10 days significantly decreased plasma blood glucose and insulin levels and enhanced the hypoglycemic response to exogenous insulin. In vitro preincubation of normal erythrocytes with insulin receptor antibody from the patient plus 4 x 10(-5) mol/l metformin markedly enhanced insulin binding to receptors, compared to cells incubated with antibody alone. This effect was apparent after 2 h, was maximal after 4 h and did not change up to 24 h. Closely similar results were found when human adipocytes were studied. Analysis of binding data confirmed the increase in both receptor number and affinity. One hour exposure of control adipocytes to metformin enhanced basal lipogenesis by more than 30%. Acute exposure of fat cells to the patient's receptor antibodies resulted in a stimulation of glucose transport and a state of severe insulin resistance. The addition of metformin to antibody in preincubation buffer strongly enhanced basal glucose incorporation into lipids, but did not prevent insulin unresponsiveness. It is suggested that metformin increases, possibly through a change in the spatial conformation of insulin receptor within the plasma membrane, the availability of pre-existing receptors to insulin binding and/or decreases the availability of specific epitopes to antibody anchoring. Further, in the model of insulin resistance described here, metformin enhanced the basal rate of glucose transport through a direct insulin-mimicking activity and/or a potentiation of the sensitivity of glucose transport to the antibody.

Adipose Tissue↗

PubMed1992

Monoclonal antibody to the human insulin receptor, but not insulin, stimulates S6 kinase via human insulin receptors mutated at three major tyrosine autophosphorylation sites.

Studies were carried out to examine the role of the major insulin receptor tyrosine autophosphorylation sites in stimulation of S6 kinase activity. For these studies, we employed HTC rat hepatoma cells transfected with and expressing human insulin receptors. In cells transfected with and expressing a large number of normal human insulin receptors (HTC-IR cells), the sensitivity of cells to insulin to stimulate S6 kinase was increased tenfold when compared to untransfected wild type HTC cells (HTC-WT cells). However, in cells transfected with and expressing a large number of mutated human insulin receptors where the tyrosines at three major autophosphorylation sites (1158, 1162, and 1163) were mutated to phenylalanines (HTC-F3 cells), there was no change in insulin sensitivity when compared to HTC-WT cells. We next studied the effect of a human-specific monoclonal antibody to the human insulin receptor, MA-5, on S6 kinase activation. In HTC-WT cells, MA-5 did not interact with endogenous rat insulin receptors and thus did not stimulate S6 kinase. In HTC-IR cells expressing normal human insulin receptors, MA-5 stimulated S6 kinase. Interestingly, MA-5, unlike insulin, was also able to stimulate S6 kinase in HTC-F3 cells expressing mutated receptors. In order to further understand the signaling mechanisms by MA-5 and insulin, two potential intermediate protein kinases were investigated. Neither insulin nor MA-5 appears to activate either microtubule-associated protein 2 (MAP-2) kinase or protein kinase C in these cells. These studies suggest therefore that: 1) insulin and MA-5 may signal S6 kinase activation by independent mechanisms that do not employ either MAP-2 kinase or protein kinase C; and 2) under certain circumstances, S6 kinase appears to be activated by mechanisms that are independent of insulin receptor tyrosine autophosphorylation.

Animals↗

PubMed1977

Phylogeny of insulin. Some evolutionary aspects of insulin production with particular regard to the biosynthesis of insulin in Myxine glutinosa.

Preceding phylogenetic studies on the occurrence of insulin have shown--e.g. by bioassays and immunocytochemical procedures--that insulin producing B-cells are present in all vertebrates and even in several invertebrates, both protostomian and deuterostomian. The most original B-cells are obviously endocrine cells of open type, situated in the mucosa of the alimentary tract. Moreover, the results of these studies show that insulin is not only a polypeptide hormone of considerable age but also that the insulin molecule seems to have been kept surprisingly stable during evolution. Best known of all non-mammalian insulins is that from the hagfish, Myxine glutinosa. It is probably the most original insulin of all in the vertebrate series. Both the amino-acid sequence and the three-dimensional structure of the dimer of hagfish insulin differ only little from those of pig insulin. The biosynthesis occurs via proinsulin and is also in most respects similar to mammalian insulin biosynthesis. There are, however, some differences. Although it readily crystallizes as tetragonal bipyramids, hagfish insulin does not form hexamers. In a test system, with isolated rat fat cells, its binding affinity is 23% and its potency 5% of that of pig insulin, a discrepancy indicating a "partial antagonism" on the receptors. Although the conversion of proinsulin to insulin seems to occur in the secretion granules, they contain no crystalline cores. Since a strictly tryptic-like enzyme was found to destroy hagfish insulin rapidly, the enzyme converting proinsulin to insulin must--in addition to a carboxy-peptidase-B-like activity--have a different specificity in Myxine.

Amino Acid Sequence↗