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  • 1
    ISSN: 1432-0428
    Keywords: Insulin analogues ; isolated fat cells ; biological potency ; lipogenesis ; inhibition of lipolysis ; combined biological action ; potentiation ; antagonism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This paper presents a survey of the biological potencies of a variety of naturally-occurring and semi-synthetic insulin analogues and a study of the joint biological action of some of these materials with native insulin. Biological activity was tested on isolated rat fat cells using lipogenesis from glucose as the metabolic index. A brief comparison using inhibition of fat cell lipolysis was included. The results indicated: 1. Analogue potencies varied considerably (0.4–100% insulin activity). Values obtained were mainly confirmatory but included two further B1-modified materials and a tricarbamylated insulin. The results supported previous indications on the relative roles of the A1, B1, and B29 residues of insulin for hormone activity. 2. Analogue bioactivities, whether assessed by stimulation of lipogenesis or inhibition of lipolysis, were similar for the four materials tested in both systems. The response of fat cells with respect to both metabolic indices occurred over a comparable range of insulin concentrations, with half maximal effects at 30–35 pmol 1−1 insulin. 3. The presence of modified insulins appeared to alter the biological action of native insulinin vitro. Small effects of both potentiation and antagonism were identified.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0428
    Keywords: Insulin structure-function ; chemically modified insulin ; proinsulin ; bioactivity of insulin analogues
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Beef insulin, pork proinsulin and four derivatives of beef insulin modified at the A1-B29 site on the molecular surface have been studied. Three derivatives had a synthetic crosslink between the A and B chains. Previous studies with these materials [2, 3 and 5] had demonstrated in vivo bioactivities which were much higher than those displayed in vitro. This paper reports experiments which explain this discrepancy. The analogues were administered at equimolar rates to anaesthetised greyhounds by a priming-dose constant infusion technique and the plasma concentrations achieved were estimated by radioimmunoassay. Proinsulin and the modified insulins were metabolised more slowly than insulin. Biopotency values, which related fall in plasma glucose concentration to the total administered dose of analogue, agreed broadly with published results of conventional in vivo bioassays. On the other hand, calculation of potency in relation to the serum concentration of analogue actually achieved, yielded results which agreed more closely with in vitro assay data. We conclude that for these analogues, reported discrepancies between in vitro and in vivo biopotencies can be largely explained by the different rates at which these materials are metabolised.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0428
    Keywords: Chemically-modified insulins ; insulin structure-function ; bioactivity and metabolism in vivo ; competitive antagonism ; hypoglycaemia ; non-esterified fatty acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The biological properties of three covalently-linked insulin dimers were studied in greyhounds. Constant infusions showed that the plasma distribution kinetics were slower for the dimers than for insulin. The metabolic clearance rates of the three dimers (10.3±0.4, 8.8±0.5, 8.2±0.5 ml· min-1· kg-1; mean ± SEM) were significantly lower than that of insulin (19±0.8 ml · min-1 · kg-1), and their hypoglycaemic effects (11.2%, 3% and 0.3%) were markedly reduced compared with their lipogenic potencies in vitro (80%, 30% and 13%, respectively). A low dose infusion of insulin or an equipotent dose of one of the dimers significantly prolonged the effects of an insulin bolus on plasma glucose but not on non-esterified fatty acids. The apparent distribution space (106.4±11.9 ml/kg) and clearance rate (14.7±0.5 ml · min-1 · kg-1) of an insulin bolus were significantly reduced by one dimer (44.5±8.4 ml/ kg and 10.7±2.8ml·min-1·kg-1) but not by the equipotent insulin infusion (102.7±8.2ml/kg and 16.4±0.07ml· min-1 · kg-1). The apparent partial competitive antagonism of insulin by the dimers that has been reported in vitro can be observed in vivo, in that antagonism of insulin metabolism was directly demonstrated with one of the dimers.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0428
    Keywords: Iodoinsulin ; insulin metabolism ; insulin analogues ; biological activity ; tracer insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Insulin, specifically substituted at the PheB1 position with 3,5-diiodotyrosine, has been tested in several biological and immunological systems. Immunoreactivity was assessed using antisera specific for different parts of the insulin molecule. Biological activity in vitro was estimated on isolated rat fat cells. In vivo bioactivity (hypoglycaemia) and metabolism (metabolic and urinary clearance rates, half-life, apparent distribution space) were measured by infusion of the material into greyhounds. The results indicated that this B1-labelled insulin preparation was biologically fully active and, unlike randomly labelled preparations of iodoinsulin, was metabolised with kinetics indistinguishable from those of the unlabelled hormone. We suggest that this material is a valid tracer for insulin, fulfilling the criteria of high specific activity and biological identity to the native hormone.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Diabetologia 18 (1980), S. 59-63 
    ISSN: 1432-0428
    Keywords: Radioimmunoassay ; chemically modified insulins ; insulin antiserum specificity ; in vivo biological activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The reactions between four insulin antisera and eighteen insulin derivatives with modifications at the A1, B1 and B29 positions have been studied using a standard double-antibody radioimmunoassay procedure. The derivatives studied had: a) single modifications at A1, B1 or B29; b) modifications at two sites with or without a crosslink between them; c) modifications at all three sites with or without a crosslink. Analysis of the results showed a clear difference in the reactivity of the antisera. One antiserum (GP 5) was highly sensitive to modifications of the B1 residue and another (Ab 1) was sensitive to A1 and B29 modifications. Thus, immunological potencies of insulin analogues derived on the basis of these reactions with the antisera give widely varying results. These antisera were used in discriminatory radioimmunoassays of chemically modified insulins in biological fluids for estimation of in vivo hypoglycaemic potencies by an infusion technique, where the knowledge of the specificity of the antisera was useful in assessing the immunological identity of immunoreactive material in plasma with the analogue infused.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0428
    Keywords: Insulin ; insulin analogues ; glucose metabolism ; euglycaemic clamp ; insulin action ; hepatoselectivity ; glucose production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Insulin analogues with relatively greater effect on hepatic glucose production than peripheral glucose disposal could offer a more physiological approach to the treatment of diabetes mellitus. The fact that proinsulin exhibits this property to a minor degree may suggest that analogues with increased molecular size may be less able than insulin to obtain access to peripheral receptor sites. Covalent insulin dimers have previously been shown to possess lower hypoglycaemic potencies than predicted by their in vivo receptor binding affinities. Reduced rates of diffusion to peripheral target tissues-might be an explanation for the lower in vivo potency compared to insulin. To test the relative hepatic and peripheral effects of covalent insulin dimers, glucose clamp procedures with D-[3-3H] glucose tracer infusions were used in anaesthetised greyhounds to establish dose-response curves for rates of hepatic glucose production and glucose disposal with insulin, NαB1, NαB′ 1,-suberoyl-insulin dimer, and NεB29, NεB′ 29,-suberoyl-insulin dimer. With NαB1, NαB′ 1,-suberoyl-insulin dimer molar potencies relative to insulin were 68%, (34–133) (mean and 95% fiducial limits), for inhibition of hepatic glucose production and 14.7%, (10.3–20.9) for glucose disposal. With NεB29,NεB′ 29,-suberoyl-insulin dimer potencies were 75%, (31–184) and 2.5%, (1.5–4.3), for inhibition of hepatic glucose production and for glucose disposal, respectively. The demonstration that both dimers exhibit a significantly greater effect on glucose production than on glucose disposal supports the suggestion that analogues with increased molecular size may exhibit reduced ability to gain access to peripheral target cells.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-0428
    Keywords: Key words Insulin ; insulin analogues ; glucose metabolism ; euglycaemic clamp ; insulin action ; hepatoselectivity ; glucose production.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Insulin analogues with relatively greater effect on hepatic glucose production than peripheral glucose disposal could offer a more physiological approach to the treatment of diabetes mellitus. The fact that proinsulin exhibits this property to a minor degree may suggest that analogues with increased molecular size may be less able than insulin to obtain access to peripheral receptor sites. Covalent insulin dimers have previously been shown to possess lower hypoglycaemic potencies than predicted by their in vivo receptor binding affinities. Reduced rates of diffusion to peripheral target tissues might be an explanation for the lower in vivo potency compared to insulin. To test the relative hepatic and peripheral effects of covalent insulin dimers, glucose clamp procedures with D-[3-3H]glucose tracer infusions were used in anaesthetised greyhounds to establish dose-response curves for rates of hepatic glucose production and glucose disposal with insulin, NαB1, NαB′ 1,-suberoyl-insulin dimer, and NɛB29, NɛB′ 29,-suberoyl-insulin dimer. With NαB1, NαB′ 1,-suberoyl-insulin dimer molar potencies relative to insulin were 68 %, (34–133) (mean and 95 % fiducial limits), for inhibition of hepatic glucose production and 14.7 %, (10.3–20.9) for glucose disposal. With NɛB29,NɛB′ 29,-suberoyl-insulin dimer potencies were 75 %, (31–184) and 2.5 %, (1.5–4.3), for inhibition of hepatic glucose production and for glucose disposal, respectively. The demonstration that both dimers exhibit a significantly greater effect on glucose production than on glucose disposal supports the suggestion that analogues with increased molecular size may exhibit reduced ability to gain access to peripheral target cells. [Diabetologia (1995) 38: 1007–1013]
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Diabetologia 20 (1981), S. 94-101 
    ISSN: 1432-0428
    Keywords: Chemically modified insulins ; gluconeogenesis ; glucose turnover ; insulin structure-function ; proinsulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A [14C]-glucose tracer infusion method was used to compare the effects of insulin infusion on glucose metabolism with the effects of infusion of three semisynthetic modified insulins and of proinsulin. Insulin produced hypoglycaemia in the anaesthetised dog by decreasing hepatic glucose production and increasing peripheral glucose utilisation. Compensatory antihypoglycaemic mechanisms eventually modified these responses. A1 B29-Diacetyl insulin exerted an hypoglycaemic effect entirely by stimulation of peripheral glucose uptake. A1-B29 crosslinked insulins and proinsulin produced hypoglycaemia almost entirely by decreasing hepatic glucose production and had little effect on tissue uptake. These observations suggest that insulin analogues may have actions in vivo that are qualitatively different from those of native insulin and suggest that certain analogues have a predominant action on the liver. This has important therapeutic implications concerning the development of semisynthetic insulins for clinical use.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Diabetologia 23 (1982), S. 391-392 
    ISSN: 1432-0428
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0931-1890
    Keywords: Key words Quercus ; Carbon allocation ; Allometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Seedling growth and morphology are thought to reflect evolutionary responses to habitat or influences of seed size. To test these hypotheses, we selected fourteen species of North American oaks differing in soil moisture habitat preference and seed size. Seedlings were grown for 1 – 2 years with abundant soil water and moderate soil nutrition in pots placed outdoors and in a common garden. Oak species native to xeric environments produced the smallest seedlings. Oaks from hydric soils had more shoot weight per unit of root weight and more height per unit of total plant weight than did mesic or xeric oaks. Essentially no differences in leaf area per unit of total plant weight were detected. Species with thinner and larger individual leaves tended to produce larger seedlings. Within species, seed size was generally unrelated to seedling growth, although results may have been complicated by uncontrolled genotypic variability. However, when species were compared, those with larger mean seed size produced larger seedlings. Root/shoot allometry, height growth and leaf thickness in the tested species may reflect evolutionary responses to soil moisture and flooding. Although seed size influenced seedling growth, no clear relationship between seed size and soil moisture habitat was found.
    Type of Medium: Electronic Resource
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