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  • 1
    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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  • 2
    ISSN: 1432-0428
    Keywords: Insulin ; despentapeptide insulin ; deshexapeptide insulin ; negative cooperativity ; insulin demerisation ; lipogenesis ; insulin binding ; insulin metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The C-terminus of the insulin B chain is essential for dimerisation and expression of negative cooperativity. In order to evaluate the possible physiological role of these phenomena, we have studied the properties in vivo and in vitro of despentapeptide insulin (B 26–30 deleted), derived from beef insulin, and deshexapeptide insulin (B25–30 deleted), derived from pork insulin. These materials do not dimerise and have 15% and 0% retention of negative cooperativity respectively. Lipogenesis potencies in rat adipocytes were: despentapeptide insulin 19.9±0.3%; deshexapeptide insulin 19.9±1.5%. Binding potencies in adipocytes were: despentapeptide insulin 22.6±7.8%; deshexapeptide insulin 13.2±3.3%. Metabolic clearance rates were reduced compared to insulin (insulin = 19.1±0.9; despentapeptide insulin = 9.7±0.8; deshexapeptide insulin = 6.4±0.6ml·min−1·kg−1 at plasma concentration 0.5 nmol/l). Hypoglycaemic potencies were reduced for both analogues (40% and 30%) when calculated on the basis of plasma concentration although both analogues and insulin were equally effective at lowering plasma glucose concentration in equimolar doses. Plasma half-disappearance time was prolonged (despentapeptide insulin=7.3±0.5; deshexapeptide insulin=9.1±0.2 min). Both analogues were full agonists and conformed to the general relationship between in vitro and in vivo properties seen with a wide range of modified insulins. They resemble other analogues with modifications which reduce receptor affinity without impairing dimerisation or negative cooperativity. The results do not support a physiological role for dimerisation or negative cooperativity.
    Type of Medium: Electronic Resource
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