Search PubMed⌕ Search

Biomedical subjects

H Reinauer

Publications and source records attributed to H Reinauer.

At least 127 records · Page 7Linked to original sources
PubMed1983

The influence of tracers on insulin binding to human erythrocytes.

We studied insulin binding to human erythrocytes using two different 125I-insulin-tracers. Erythrocytes of 8 normal subjects were examined using [mono-125II-(Tyr A 14)insulin as tracer. Three of these erythrocyte preparations were examined simultaneously using [125I]insulin, which was randomly iodinated by the chloramine-T-method. Data were analysed by a computerized non-linear least-squares procedure both on the basis of one and two class receptor models. Only the one class receptor model yielded consistent results. When the two class receptor model was applied the low affinity branch of the Scatchard plot was not reproducible. On the basis of the one class receptor model the number of receptor sites was lower (R0 = 0.046 +/- 0.006 nmol/l equivalent to 6.3 +/- 0.8 receptors/erythrocyte) with [mono-125I-(Tyr A 14)]insulin as compared to [125I]insulin randomly iodinated by the chloramine-T method (R0 = 0.070 +/- 0.008 nmol/l equivalent to 9.6 +/- 1.1 receptors/erythrocyte). Conversely, the affinity of the [mono-125I-(Tyr A 14)]insulin was higher (Ka = 2.6 +/- 0.3 x 10(9) l . mol-1 vs. 1.9 +/- 0.2 x 10(9) l . mol-1.

Adult↗
PubMed1983

[Fat infusion and carbohydrate metabolism].

In non-insulin-dependent diabetics (type II), in obese patients and in critically ill patients, there is an insulin resistant metabolic state. The mechanism of insulin resistance can be defined in states of reduced insulin sensitivity of the receptor, reduced insulin responsiveness, and a combination of these two hormone resistant states. The molecular mechanism or the insulin resistance may be localized prior to the interaction of insulin with the receptors (pre-receptor defect), alteration of the interaction of insulin with its receptor, and disorders associated with the alteration of the intracellular steps in insulin action (post-receptor defect). In acutely ill patients the number of insulin receptors are diminished and a reduced sensitivity and reduced responsiveness of the metabolism to insulin action may result. At the intracellular level there is an inhibition of the phosphofructokinase and the pyruvatedehydrogenase complex. In this given metabolic state fatty acids are preferentially metabolized, which may be supported by intravenous fat. Later, if no special restrictions against the lipid component are given, the parenteral nutrition should use all the three main components: lipids, glucose and amino acids.

Biological Transport↗
PubMed1982

The fate of insulin in cardiac muscle. Studies on isolated muscle cells from adult rat heart.

Isolated muscle cells from adult rat heart were used to study myocardial degradation of insulin and the reactions after the initial binding event. After 60 min of association at 37 degrees C, 90% of specifically bound insulin could be dissociated from the cells; this fraction remained unaltered under steady-state conditions (up to 180 min). To assess the nature of cell-associated radioactivity, cardiocytes were solubilized and filtered on Sephadex G-50. After 5 min of association only intact insulin was observed, whereas under steady-state conditions 4% of 125I-labelled insulin bound to the cells was degraded to iodotyrosine-containing fragments. The Km for insulin degradation by isolated heart cells was estimated to be 1.75 x 10(-7)M. Receptor-mediated insulin degradation was studied by examination of the nature of radioactivity released by the cells after different times of association. After 5 min 83% of dissociating material consisted of intact insulin, whereas this fraction decreased to 50% under steady-state conditions. Treatment of cells with the lysosomotropic agent chloroquine (0.1 mM) significantly decreased the fraction that was eluted at the internal column volume. This study demonstrates that insulin degradation by the heart cell occurs by a receptor-independent and a receptor-dependent mechanism. The latter may involve internalization and a lysosomal pathway.

Animals↗
PubMed1982

Isolation and characterization of three different forms of arylamidase from rat skeletal muscle.

An arylamidase hydrolysing L-leucine-4-nitroanilide was extracted from rat skeletal muscle homogenate and purified by means of anion-exchange chromatography on DEAE-Sephadex A-50 followed by gel filtration on Sephadex G-150 and Sepharose 6B. The enzyme was isolated in the form of three different protein complexes that differ in molecular weight, kinetic data, and sensitivity to metal ions. As studied by SDS-gel electrophoresis and repeated gel chromatography on Sepharose 6B these forms are: 1, a stable monomer (A1) of Mr 122000; 2. A stable dimer (A2) of Mr 244000; and 3. a stable polymer (A3) of more than Mr 4.10(6). The arylamidase was optimally active at pH 7.3 and did not require metal ions. Treatment with 1,10-phenanthroline resulted in complete inactivation, the activity could be restored by the addition of manganous chloride. The sulphhydryl-blocking reagent 4-hydroxymercuribenzoate strongly inactivated the arylamidase, this inhibition could be reversed by the addition of 2-mercaptoethanol. Addition of phenylmethylsulfonyl fluoride had no effect on the enzyme activity. Furthermore, the influence of metal ions as well as the substrate specificity were investigated and compared for all three forms of arylamidase.

Aminopeptidases↗
PubMed1982

[Effect of lipid infusions on triglyceride and protein metabolism].

In metabolically healthy volunteers we investigated the influence of long and medium chained triglycerides on the kinetic of the free fatty acids in blood and on protein metabolism. During a three hour infusion of lipid emulsion (infusion rate 120 mg/kg BW X h) consisting of 50% medium and 50% long chained triglycerides we observed a significant increase of the concentrations of the medium chained free fatty acids (caprylic and capric acid), which decreased down to basic values with a half life of 30 minutes immediately after the infusion period. The total concentration of free fatty acids was higher during the infusion of a MCT/LCT mixture than during the infusion of pure LCT. Glucose infused simultaneously reduced the metabolism of the free fatty acids. MCT induced higher ketonemia and ketonuria than LCT, the ketogenesis could be suppressed by additional glucose. Compared to the glycerol control infusion the total nitrogen excretion was reduced under lipid infusion. Beside the lower excretion of Glu + Gln and Ala the excretion of 3-methylhistidine was reduced, which indicates a decreased on muscle protein turnover as referred to increased free fatty acids and the ketone body concentrations respectively.

Adult↗
PubMed1982

Studies on proteolytic activities in heart muscle of diabetic rats.

Induction of diabetes mellitus in rats following injection of streptozotocin caused reduction in rate of gain of heart weight, of protein and of DNA content in the first two weeks. During the same time interval the overall activity of acid proteinases (cathepsin D), of alkaline proteinases and of proteinase inhibitors was measured in heart muscle homogenates. No statistically significant differences were detected compared with the proteinase activities in control rats. In contrast, total aminopeptidase activity in diabetic hearts was consistently lower than in control hearts. Earlier studies on rat skeletal muscles have shown that induction of diabetes mellitus is followed by a substantial increase of alkaline proteinase as well as aminopeptidase activities. These findings are contrasted by present data obtained with heart muscle of diabetic rats, suggesting that this tissue responds differently to insulin deficiency.

Aminopeptidases↗
PubMed1982

[A method for the gas chromatographic determination of long and medium chain free fatty acids in serum].

Free fatty acids in serum were determined by gas chromatography after esterification with boron tri-fluoride-methanol. Following prepurification of the serum lipid fractions by thin layer chromatography, the described analytical procedure selectively determines the medium and long chain free fatty acids. Accuracy and precision were tested. The method is suitable for the analysis of fatty acid kinetics in blood, following lipid infusions.

Chromatography, Gas↗
PubMed1981

Antagonistic effects of endurance training and testosterone on alkaline proteolytic activity in rat skeletal muscles.

Endurance swimming training for 8 weeks led to an increase by about 50% of alkaline proteinase activity in musculus extensor digitorum longus and about 10% in musculus soleus of normal male rats as compared to sedentary control rats. This exercise-mediated increase of proteolytic activity was prevented by the simultaneous administration of 10 mg testosterone propionate/kg body weight twice a week. The data suggest that testosterone has a regulatory effect on the alteration of the protein-degradative mechanism during endurance training.

Animals↗
PubMed1981

Purification of the insulin receptor protein from porcine liver membranes.

Insulin receptor protein was isolated from porcine liver membranes. Starting with 600 g of liver, the plasma membrane-enriched fraction with extracted with detergent. After AcA 34 gel chromatography, affinity chromatography and DEAE-Sephacel chromatography an insulin receptor preparation was obtained which was 2500-fold purified over crude homogenate and which had a specific binding activity of up to 1 x 10(-9) mol insulin/mg protein. The yield was 200 micrograms. Analysis of binding data according to Scatchard resulted in curvilinear plots and substantially the same affinity constants with the membrane preparation and also with the purified insulin receptor protein. Dodecyl sulfate gradient gel electrophoresis of the purified insulin receptor protein showed up to eight protein bands in the range from 38 to 175 kDa. The main bands indicate an apparent molecular mass of 38, 60, 80, 120 and 150 kDa for the insulin receptor-binding protein subunits.

Animals↗
PubMed1981

Studies on the alkaline proteinase system in rat skeletal muscle.

The alkaline proteolytic activity, as measured with azocasein as substrate, is significantly increased in the musculus extensor digitorum longus 8 days after induction of diabetes mellitus, whereas in soleus muscle, a slightly lower activity is measured when compared to control rats. Ethyleneglycol extraction of the activity from muscles of normal rats and subsequent fractionation by gel filtration revealed three distinct proteinase activities, corresponding to mol. wts. of 120000, 70000 and 18000. Induction of diabetes mellitus in rats is followed by a loss of the 120000 mol.wt. component. Treatment of the diabetic rats with compound 48/80 results in a complete loss of all three proteinase peaks. The activity of a proteinase inhibitor with an apparent mol. wt. of 60000 was unaffected by these manipulations.

Animals↗
PubMed1981

[Hyperglycemia as a risk factor in pregnancy (author's transl)].

Glycosylated hemoglobins were used for the retrospective assessment of glucose metabolism, for therapy control, and as predictor of the weight of the newborn. Glycosylated hemoglobins were determined with the microcolumn method in 50 pregnant diabetics, in 11 overweight pregnant women, in 11 pregnant women under tocolytic treatment, and in 28 metabolically healthy women. Whereas the levels of glycosylated hemoglobins were found to be reduced in metabolically healthy women, the corresponding levels were increased in tocolytically treated, adipose, and diabetic pregnant women. The HbAI values correlated with the mean values of the daily blood glucose profiles (r = 0.79 - 0.94) and decreased during improvement of the metabolic state. A statistic correlation could not be established between the maternal HbAI and the weight of the newborn as the pregnancy period is shortened by dearrangement of the carbohydrate metabolism.

Blood Glucose↗
PubMed1981

[Comparison of analytical methods for the estimation of glycosylated haemoglobins (author's transl)].

The glycosylated haemoglobins of 26 different blood samples were analysed by six different methods; the regression lines and the correlation coefficients were calculated from the analytical data. The best separation and estimation of the fast haemoglobin fractions were achieved by high performance liquid chromatography (HPLC). Therefore HPLC is regarded as the reference method for the analysis of fast haemoglobin fractions. Microcolumn chromatography or the thiobarbituric acid method are recommended for routine analysis in clinical laboratories. Since the labile aldimine (Schiff's base) can be calculated from the analytical data or destroyed by appropriate methods, this glycosylated haemoglobin fraction does not interfere with the results.

Chromatography, Gel↗
PubMed1980

The influence of testosterone on the alkaline proteolytic activity in rat skeletal muscle.

The effects of testectomy and subsequent administration of testosterone propionate on the activity of the alkaline proteinases in rat skeletal muscle were investigated. Castration of the mature rat was followed by a short-term delay in protein accretion in skeletal muscle tissue as measured by the protein/DNA ratio and was paralleled by a 2-3-fold increase in specific activity of the alkaline proteinase(s). This increase of proteolytic activity was equally significant when expressed relative to microgram DNA. Although the gain in body weight was significantly lower in the castrated rats, nevertheless the protein/DNA ratio in muscle after 6 weeks approximated the values of sham-operated control rats without normalization of the proteolytic activity. Treatment of the castrated rats with testosterone propionate resulted in restoring normal levels of previously elevated levels of alkaline proteolytic activity in muscle tissue. The normalization of enzyme activity as well as protein accretion in muscle was dose-dependent. Treatment of the rats with a low dose (0.1 mg/day) of testosterone propionate failed to restore the proteolytic activity, but led to a small increase of th protein/DNA ratio as well as to a progressive increase in body weight. These data indicate a regulatory role of testosterone in the adaptive behaviour of the alkaline proteolytic system in rat skeletal muscle.

Animals↗
PubMed1980

Characteristics of insulin receptors in the heart muscle: binding of insulin to isolated muscle cells from adult rat heart.

Adult rat heart muscle cells obtained by perfusion of the heart with collagenase have been used to characterize the insulin receptors by equilibrium binding and kinetic measurements. Binding of 125I-labelled insulin to heart cells exhibited a high degree of specificity; it was dependent on pH and temperature, binding at steady state increased with decreasing temperatures. Above 70% of the radioactivity bound at equilibrium at 25 degrees C could be dissociated by addition of an excess of unlabelled insulin. 54 and 40% of 125I-labelled insulin was degraded by isolated heart cells after 2 h at 37 degrees C and 4 h at 25 degrees C, respectively. This degrading activity was effectively inhibited by high concentrations of albumin. Equilibrium binding studies were conducted at 25 degrees C using insulin concentrations ranging from 2.5 x 10(-11) mol/l to 10(-6) mol/l. Scatchard analysis of the binding data resulted in a curvilinear plot (concave upward), which was further analyzed using the average affinity profile. The empty site affinity constant was calculated to be 9.5 x 10(7) l/mol with a total receptor concentration of 3.4 x 10(6) sites per cell. The presence of site-site interactions of the negative cooperative types among the insulin receptors has been confirmed by kinetic experiments. The rate of dilution induced dissociation was enhanced in the presence of native insulin (5 x 10(-9) mol/l), both, under conditions of low and high fractional saturation of receptors. These studies demonstrate the presence of specific insulin receptors in isolated muscle cells from adult rat heart and provide a useful model for the study of insulin action on the heart.

Animals↗
PubMed1980

Binding of insulin to bovine liver plasma membrane. Use of insulin analogues modified at the A1 residue.

Bovine liver plasma membranes [Rösen, Ehrich, Junger, Bubenzer & Kühn (1979) Biochim. Biophys. Acta587, 593-605] show similar insulin-binding characteristics, as evaluated by Scatchard analysis, to those of membrane systems from other species. However, the dissociation rate of bound insulin cannot be accelerated by the addition of insulin, in contrast with membranes isolated from rat liver. The dissociation rate is strongly dependent on the pH. Although dependent on temperature, the total capacity of binding sites is minimally changed, but the number of high-affinity sites is increased 2-3-fold, by lowering the incubation temperature. These data might be interpreted by assuming a single population of receptors whose distribution between different affinity states depends on temperature. In competition studies, most of the modified insulins examined show a close correlation between binding, determined in plasma membranes from bovine liver, and biological activity, measured in adipocytes. The hypothesis that a positive charge on the A1 residue may be favourable for binding is supported by experiments with an isosteric pair of insulins modified at this residue ([carbamoyl-Gly(A1)]- and [amidino-Gly(A1)]insulin) and with modified insulins carrying one or more positive charges on the A1 residue ([Arg-Gly(A1)]-, [Arg-Arg-Gly(A1)]-, [Arg-Arg-Arg-Gly(A1)]- and [Lys-Arg-Gly(A1)]insulin). The latter insulin derivatives show a higher binding activity for plasma membranes from bovine, porcine and rat liver than expected from their biological activities in adipocytes.

Animals↗