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  • 1
    Electronic Resource
    Electronic Resource
    Binding and molecular weight properties of the insulin receptor from omental and subcutaneous adipocytes in human obesity (1984)
    Springer
    Diabetologia 27 (1984), S. 447-453 
    Details
    ISSN: 1432-0428
    Keywords: Insulin receptor ; obesity ; adipocyte ; subcutaneous fat ; omental fat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The insulin binding properties and the molecular weights of the insulin receptor and its insulin binding subunit were studied in omental and subcutaneous adipocytes prepared from obese- and normal-weight subjects. Insulin binding by such adipocytes was decreased in obesity when the binding activity was expressed per unit of cell surface area. No significant difference from the lean controls was evident, however, when binding was calculated on a per cell basis, indicating that the total receptor content of the cells from the obese subjects was not altered. In addition, the normal difference in the receptor binding affinities previously reported between omental and subcutaneous cells from lean individuals was unaffected by the obese condition. Studies of the molecular weight of the non-reduced insulin receptor in fat cell membranes prepared from pieces of omental and subcutaneous fat demonstrated a major receptor species of 390–425K Mr. In contrast, adipocytes isolated by collagenase treatment of the fat had heterogenous non-reduced receptor species of Mr 355K, 285K and small amounts of 427K and 182K. Although different non-reduced receptor species were evident depending on the adipocyte receptor preparation (e.g. isolated adipocytes or fat cell membranes), no differences were found between obese and lean controls or between subcutaneous and omental receptors when the appropriate comparisons were made. Upon sulphydryl reduction, all receptor preparations had a major binding subunit of 125K Mr. In conclusion, obesity is characterized by a dilution of the insulin receptor over the adipocyte cell surface in the absence of a change in total cellular content of receptors. The difference in insulin binding affinities between omental and subcutaneous adipocytes could not be explained by an alteration in receptor molecular weight.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00273909
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  • 2
    Electronic Resource
    Electronic Resource
    Regional difference in insulin inhibition of non-esterified fatty acid release from human adipocytes: relation to insulin receptor phosphorylation and intracellular signalling through the insulin receptor substrate-1 pathway (1998)
    Springer
    Diabetologia 41 (1998), S. 1343-1354 
    Details
    ISSN: 1432-0428
    Keywords: Keywords Tyrosine kinase ; insulin receptor substrate-1 ; phosphaditylinositol 3-kinase ; catecholamines ; re-esterification ; lipolysis.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Increased mobilization of non-esterified fatty acids (NEFA) from visceral as opposed to peripheral fat depots can lead to metabolic disturbances because of the direct portal link between visceral fat and the liver. Compared with peripheral fat, visceral fat shows a decreased response to insulin. The mechanisms behind these site variations were investigated by comparing insulin action on NEFA metabolism with insulin receptor signal transduction through the insulin receptor substrate-1 (IRS-1) pathway in omental (visceral) and subcutaneous human fat obtained during elective surgery. Insulin inhibited lipolysis and stimulated NEFA re-esterification. This was counteracted by wortmannin, an inhibitor of phosphaditylinositol (PI) 3-kinase. The effects of insulin on antilipolysis and NEFA re-esterification were greatly reduced in omental fat cells. Insulin receptor binding capacity, mRNA and protein expression did not differ between the cell types. Insulin was four times more effective in stimulating tyrosine phosporylation of the insulin receptor in subcutaneous fat cells (p 〈 0.001). Similarly, insulin was two to three times more effective in stimulating tyrosine phosphorylation of IRS-1 in subcutaneous fat cells (p 〈 0.01). This finding could be explained by finding that IRS-1 protein expression was reduced by 50 ± 8 % in omental fat cells (p 〈 0.01). In omental fat cells, maximum insulin-stimulated association of the p85 kDa subunit of PI 3-kinase to phosphotyrosine proteins and phosphotyrosine associated PI 3-kinase activity were both reduced by 50 % (p 〈 0.05 or better). Thus, the ability of insulin to induce antilipolysis and stimulate NEFA re-esterification is reduced in visceral adipocytes. This reduction can be explained by reduced insulin receptor autophosphorylation and signal transduction through an IRS-1 associated PI 3-kinase pathway in visceral adipocytes. [Diabetologia (1998) 41: 1343–1354]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001250051075
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  • 3
    Electronic Resource
    Electronic Resource
    Altered action of glucagon on human liver in Type 2 (non-insulin-dependent) diabetes mellitus (1987)
    Springer
    Diabetologia 30 (1987), S. 323-326 
    Details
    ISSN: 1432-0428
    Keywords: Glucagon receptor ; adenylyl cyclase ; cyclic AMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Glucagon may play a role in the metabolic derangements of overt Type 2 (non-insulin-dependent) diabetes mellitus. We therefore have evaluated the early steps in glucagon action by investigating the hormone-sensitive adenylyl cyclase system in liver membranes from seven Type 2 diabetic patients with fasting hyperglycaemia and two-fold elevations in plasma glucagon. The comparison was made with seven control subjects matched for age, sex and body weight. Glucagon receptor binding was almost identical in the two groups. There were, however, marked alterations in the adenylyl cyclase activity in membranes from the diabetic patients. This activity was reduced by 35–50% when compared to control activity. Basal cyclase activity, as well as the activity after stimulation with glucagon or with agents (i. e., sodium fluoride and forskolin) that act beyond the glucagon receptor, was significantly decreased (p〈0.05, p〈0.001 respectively). In conclusion, uncontrolled Type 2 diabetes in associated with an over-all loss of responsiveness of the hormone-sensitive adenylyl cyclase in human liver, which apparently results from post-receptor alterations. This change may provide a mechanism for reducing the effect of hyperglycagonaemia in Type 2 diabetes mellitus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00299025
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Defective insulin receptor tyrosine kinase in human skeletal muscle in obesity and Type 2 (non-insulin-dependent) diabetes mellitus (1987)
    Springer
    Diabetologia 30 (1987), S. 437-440 
    Details
    ISSN: 1432-0428
    Keywords: Glucose ; insulin ; receptor ; metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The tyrosine kinase activity of the insulin receptor was investigated in skeletal muscle biopsies from insulin-resistant males with obesity or with Type 2 (non-insulin-dependent) diabetic males who were lean or overweight. The kinase activity of the receptor from all three groups of insulin-resistant subjects was 40% less when compared to the activity of lean control subjects. This alteration was present in the absence of changes in the level of the insulin receptor on its insulin binding characteristics. We conclude that the tyrosine kinase activity of the skeletal muscle insulin receptor is defective in obesity and Type 2 diabetes, and that this alteration contributes to the insulin-resistant characteristics of both disorders.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00292549
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    The hypophyseal pars tuberalis is enriched with distinct phosphotyrosine-containing proteins not detected in other areas of the brain and pituitary (1993)
    Springer
    Cell & tissue research 272 (1993), S. 499-507 
    Details
    ISSN: 1432-0878
    Keywords: Adenohypophysis ; Pars tuberalis ; Insulin receptor ; Median eminence ; Phosphotyrosine ; Tyrosine kinases ; Rat (Sprague Dawley)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The regulation of cell activity, growth and metabolism by a number of growth factor receptors and proto-oncogene products involves tyrosine kinase activity resulting in autophosphorylation of the receptors and production of phosphorylated tyrosine-containing protein substrates. The identification and precise localization of phosphotyrosine (PY)-containing proteins are first steps in elucidating the functional role of tyrosine kinases in the modulation of the central nervous system and related areas. In the present report, we describe PY-containing proteins in the median eminence and adjacent pars tuberalis of the rat adenohypophysis by immunocytochemistry using light and electron microscopy, and by Western blotting analysis. PY-immunoreactivity was found to be most intense throughout the cytoplasm of a population of epithelial pars tuberalis cells. Polyacrylamide gel electrophoresis and Western blotting of tissue extracts from various brain and pituitary regions demonstrated a general pattern of 4 major bands of PY-proteins, with an additional dense band representing a 44 kDa protein that was highly phosphorylated on tyrosines and that was exclusively found in the pars tuberalis. Additional investigation for the presence of insulin receptors, a tyrosine kinase previously correlated with the distribution of PY-proteins, demonstrated a receptor localization in axons and nerve terminals in the external and internal zone of the median eminence. However, the large amount of different PY-proteins present in the secretory cell population of the pars tuberalis could not be attributed to the insulin receptor. Our findings demonstrate that there is a large amount of cell-specific tyrosine kinase activity in the median eminence and contacting the pars tuberalis; these may play a significant role for transduction of biological signals or metabolic regulation in the neuroendocrine region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318556
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    Paper (German National Licenses)
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