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Biomedical subjects

H Reinauer

Publications and source records attributed to H Reinauer.

At least 109 records · Page 6Linked to original sources
PubMed1985

Glucose uptake in isolated heart cells: studies on the role of insulin.

Glucose transport in cardiac myocytes is highly sensitive to stimulation by insulin. The concentration of half-maximal action (3 X 10(-10) mol/l) corresponds to the high-affinity constant of the insulin receptor. Insulin action on the glucose carrier is exclusively due to an increase in Vmax with no changes in Km. The onset of insulin action is preceded by a lag phase of about 20 s and found to be ATP-dependent. Neither the sodium pump, nor calcium, but magnesium appears to be involved in the mediation of insulin action.

3-O-Methylglucose↗
PubMed1984

Loss of fast-twitch isomyosins in skeletal muscles of the diabetic rat.

By means of pyrophosphate electrophoresis the myosin isoenzyme pattern of two fast-twitch skeletal muscles (extensor digitorum longus, gastrocnemius) and one slow-twitch muscle (soleus) was investigated in control rats and was compared with that of rats 4 weeks after induction of diabetes mellitus by streptozotocin injection. In the fast-twitch muscles the isomyosin pattern consisting of FM1 (fast isomyosin 1), FM2 and FM3 was strongly affected by diabetes, resulting in an extensive loss of FM1 and a substantial decrease of FM2. These changes were also apparent when the light chains of the fast isomyosins were analysed by two-dimensional electrophoresis: LC3f (myosin light chain 3f) largely disappeared and LC2f was significantly diminished. In contrast, the isomyosin pattern in soleus muscle, consisting of SM1 (slow isomyosin 1) and SM2, was not affected by the diabetic state, and two-dimensional electrophoresis revealed a normal light-chain pattern of LC1sa, LC1sb and LC2s. These results indicate that the isomyosins of slow-twitch oxidative myofibres are more resistant to the hormonal and metabolic disorders during diabetes mellitus than are the isomyosins of fast-twitch fibres.

Animals↗
PubMed1984

Identification of four distinct serine proteinase inhibitors in rat skeletal muscle.

The serine proteinase inhibitory capacity in the cytosolic fraction of rat skeletal muscle tissue is accounted for by several discrete inhibitory activities. Three of these activities are identical with the proteinase inhibitors alpha 1-proteinase inhibitor, rat proteinase inhibitor I and rat proteinase inhibitor I I respectively, which have been recently characterized as major serine proteinase inhibitors in rat serum (Kuehn, L., Rutschmann, M., Dahlmann, B. and Reinauer, H. (1984) Biochem. J. 218, in the press). The other inhibitor molecule, having an Mr of about 15 000, appears to be an endogenous inhibitor.

Animals↗
PubMed1984

Proteinase inhibitors in rat serum. Purification and partial characterization of three functionally distinct trypsin inhibitors.

Three different serine proteinase inhibitors were isolated from rat serum and purified to apparent homogeneity. One of the inhibitors appears to be homologous to alpha 1-proteinase inhibitor isolated from man and other species, but the other two, designated rat proteinase inhibitor I and rat proteinase inhibitor II, seem to have no human counterpart. alpha 1-Proteinase inhibitor (Mr 55000) inhibits trypsin, chymotrypsin and elastase, the three serine proteinases tested. Rat proteinase inhibitor I (Mr 66000) is active towards trypsin and chymotrypsin, but is inactive towards elastase. Rat proteinase inhibitor II (Mr 65000) is an effective inhibitor of trypsin only. Their contributions to the trypsin-inhibitory capacity of rat serum are about 68, 14 and 18% for alpha 1-proteinase inhibitor, rat proteinase inhibitor I and rat proteinase inhibitor II respectively.

Animals↗
PubMed1984

Inhibition of carnitine palmitoyltransferase 1 by phenylalkyloxiranecarboxylic acid and its influence on lipolysis and glucose metabolism in isolated, perfused hearts of streptozotocin-diabetic rats.

The metabolic action of the new hypoglycemic compound, sodium-2-(5-[4-phenyl]-pentyl)-oxirane carboxylate (POCA), was studied in isolated perfused hearts of control and streptozotocin-diabetic rats. Perfusion with POCA selectively inhibited the activity of carnitine palmitoyltransferase 1, but had no influence on the activities of carnitine palmitoyltransferase 2, pyruvate dehydrogenase, and triglyceride lipase. Perfusing the hearts of streptozotocin-diabetic rats with POCA (10 mumol/L) reduced myocardial lipolysis and accelerated the rate of pyruvate and lactate outflow as well as pyruvate oxidation. The insulin sensitivity of the diabetic hearts with respect to lactate production and glucose oxidation was restored by perfusion with POCA. In contrast, defective glycogen synthesis in the diabetic hearts was not influenced by POCA. These data suggest that: (1) The insulin resistance of the glucose-perfused diabetic heart results from two different post-insulin-receptor defects. Whereas the disturbances of glucose oxidation are mediated by the excessive metabolism of endogenous triglycerides, the reason for the disturbed glycogen synthesis remains unclear. (2) Since in vitro perfusion with POCA partially restored the insulin sensitivity of the diabetic hearts, insulin-receptor defects should be of minor importance for the insulin resistance of diabetic hearts. (3) Since POCA inhibited carnitine palmitoyltransferase 1 and reduced the rate of lipolysis but had no effect on triglyceride lipase activity, we assume that product inhibition plays an important role in the regulation of myocardial lipolysis. In summary, inhibition of carnitine palmitoyltransferase 1 by POCA is suggested to be a useful approach for restoring insulin sensitivity depressed by an excessive metabolism of lipids.

Acyltransferases↗
PubMed1984

Reduced transcoronary exchange and prostaglandin synthesis in diabetic rat heart.

In perfused hearts of streptozotocin-diabetic rats the kinetics of a fluoresce indicator transit was measured after pulse injection of FITC-dextran 3. The fluorescence changes on the left ventricle could be described by two pseudo first-order processes with half times in the range of seconds (t/2) corresponding to the intravascular washout and a slow process (T/2) corresponding to the exchange between the extra- and the intravascular space. In diabetes both half times became prolonged, and the amount of FITC-dextran 3 exchanged between the two compartments was reduced, indicating an impaired transcoronary transport in diabetic hearts. There was a time-dependent reduction in the basal release of prostacyclin in hearts of control and diabetic rats. However, studied hearts of diabetic rats released less 6-keto-prostaglandin F1 alpha (PGF1 alpha) than controls. This impaired release of 6-oxo-PGF1 alpha could be prevented partly by adrenalectomy. Because diabetic hearts release more 6-oxo-PGF1 alpha than controls after application of arachidonic acid, these data suggest that the supply of arachidonic acid for the synthesis of prostaglandins is impaired in diabetes, but not the cyclooxygenase pathway itself. The reduced transcoronary transport and the impaired synthesis of prostacyclin might be early steps in the development of microangiopathic myocardial alterations in diabetes.

6-Ketoprostaglandin F1 alpha↗
PubMed1984

Effect of EDTA on insulin binding and insulin action in isolated cardiocytes from adult rat. Evidence for a functional role of low-affinity insulin receptors.

Calcium-tolerant myocytes from the adult rat heart were used to study the effects of EDTA on insulin binding and insulin action. Treatment of cardiocytes with EDTA resulted in a 60% inhibition of insulin binding. This effect was partially reversible by subsequent addition of calcium or magnesium. Scatchard analysis of equilibrium binding data in the presence of calcium and magnesium showed a curvilinear plot with a high-affinity segment having a Kd of 5.7 X 10(-10) mol/L. In the presence of EDTA a linear Scatchard plot was observed with a Kd of 5.6 X 10(-9) mol/L. The total number of insulin receptors remained unaltered under these conditions. In contrast to insulin binding, insulin internalization was not affected by EDTA treatment. Insulin action was studied by measuring the effect of the hormone on the transport of 3-O-methylglucose. Half-maximal action occurred at an insulin concentration of 3 X 10(-10) mol/L and 10(-8) mol/L in control and EDTA-treated cells, respectively. Maximal transport stimulation, however, was not significantly different in both groups (130% and 106%, respectively). In conclusion, low-affinity insulin receptors in cardiac myocytes mediate a biologic response comparable to that of high-affinity sites; moreover, they may be involved in the process of internalization in this tissue. The data suggest a functional role of low-affinity insulin receptors in cardiac muscle.

3-O-Methylglucose↗
PubMed1984

[3-Methylhistidine as a parameter for the determination of muscle proteolysis in the post-stress syndrome and in diabetes mellitus].

The renal excretion of 3-methylhistidine was measured in healthy human volunteers under different diets. The excretion of 3-methylhistidine and total nitrogen was increased in 8 surgical patients. These findings are referred to an increased proteolysis mainly in the skeletal muscle. In four insulin-dependent diabetic patients (IDDM) the excretion of 3-methylhistidine into urine was increased only when referred to body weight. The interpretation of the 3-methylhistidine/creatinin ratio is discussed. In diabetic patients the total nitrogen excretion seems to be a better parameter for protein turnover than 3-methylhistidine. The data suggest that 3-methylhistidine excretion into urine is a suitable parameter for the determination of muscle protein turnover.

Adult↗
PubMed1983

Insulin action on cardiac glucose transport. Studies on the role of the Na+/K+ pump.

Isolated muscle cells from adult rat heart have been used to study the relationship between myocardial glucose transport and the activity of the Na+/K+ pump. 86Rb+-uptake by cardiac cells was found to be linear up to 2 min with a steady-state reached by 40-60 min, and was used to monitor the activity of the Na+/K+ pump. Ouabain (10(-3) mol/l) inhibited the steady-state uptake of 86Rb+ by more than 90%. Both, the ouabain-sensitive and ouabain-insensitive 86Rb+-uptake by cardiac cells were found to be unaffected by insulin treatment under conditions where a significant stimulation of 3-O-methylglucose transport occurred. 86Rb+-uptake was markedly reduced by the presence of calcium and/or magnesium, but remained unresponsive towards insulin treatment. Inhibition of the Na+/K+ pump activity by ouabain and a concomitant shift in the intracellular Na+ :K+ ratio did not affect basal or insulin stimulated rates of 3-O-methylglucose transport in cardiac myocytes. The data argue against a functional relationship between the myocardial Na+/K+ pump and the glucose transport system.

Animals↗
PubMed1983

Susceptibility of muscle soluble proteins to degradation by mast cell chymase.

We investigated the in vitro susceptibility of muscle soluble proteins to the major alkaline proteinase (chymase) from skeletal muscle tissue, an enzyme originating from intramuscular mast cells, but also present in certain muscle fibers. Cytoplasmic proteins from rat skeletal muscle tissue were fractionated into four groups according to their different isoelectric points: fraction A (pI 9.5-7.0), B (pI 7.0-5.6), C (pI 5.5-4.5) and D (pI 5.3-3.5). Chromatography of these fractions on octyl-Sepharose CL-4B revealed the presence of a higher percentage of hydrophobic proteins in fraction C and D as compared to fraction A and B. In vitro degradation of these protein fractions by chymase, isolated from rat skeletal muscle tissue, was monitored (a) by measuring the ability of these proteins to bind Coomassie G-250, and (b) by analyzing the digestion mixture in isoelectric focusing gels. Both methods revealed fraction B proteins to be degraded very rapidly. While there was also a significant breakdown of fraction A proteins, fraction C and D proteins were degraded only very slowly, if at all. These differences in degradability are not due to the presence of a proteinase inhibitor in fraction C and D. The results suggest that mast cell chymase preferentially degrades those groups of muscle soluble proteins, the constituents of which have neutral to basic isoelectric points and a relatively low surface hydrophobicity.

Animals↗
PubMed1983

Identification of three high molecular mass cysteine proteinases from rat skeletal muscle.

Three cysteine proteinases were isolated from the post-myofibrillar fraction of rat skeletal muscle. Proteinase I preferentially hydrolyzes Z-Phe-Arg-NMec with pH optimum at 8-9. The enzyme activity is stabilized by ATP against thermal inactivation. Proteinase II and III were not resolved by anion-exchange chromatography, by affinity chromatography on Arginine-Sepharose or by gel filtration. Proteinase II, splitting Bz-Val-Gly-Arg-NMec optimally at pH 10-10.5, is inactivated by ATP, whereas Proteinase III, hydrolyzing Suc-Ala-Phe-NMec at pH 7-7.5 is not affected by the nucleotide. The molecular mass of proteinase I is about 750 000 and that of proteinase II and III is about 650 000, as determined by gel filtration.

Animals↗
PubMed1983

Insulin action on the glucose transport system in isolated cardiocytes from adult rat.

Calcium-tolerant myocytes from the adult rat heart were used to study the effects of insulin on the kinetics of myocardial 3-0-methylglucose transport at 37 degrees C. Insulin increased the initial velocity of sugar influx without affecting the equilibrium uptake values. Maximal stimulation averaged 50-80%, with a half-maximal response at an insulin concentration of 0.1 nM and maximal stimulation occurring at 1 nM. The onset of insulin action was preceded by a lag-phase of 20 s, reaching maximal action by 60 s. The Vmax. of the glucose transport system was increased from 160 to 287 nmol/min per 10(6) cells with an unaltered affinity. Neither extracellular nor intracellular calcium was found to be involved in the stimulatory action of insulin. Removal of intracellular magnesium resulted in a loss of insulin action. This study demonstrates that activation of the cardiac glucose transporter by insulin is due exclusively to an increase in the maximal velocity representing one of the very early effects of insulin on myocardial metabolism. The data suggest involvement of magnesium in the transmission of the insulin signal.

3-O-Methylglucose↗
PubMed1983

[Effect of orally-administered triglycerides on muscle proteolysis in the rat].

Earlier studies in man could demonstrate that intravenous lipids decreased the concentration of amino acids in plasma (to 50%). In short- and long-term experiments in rat the effect of orally applied olive-oil on the concentration of amino acids in blood, on the excretion of 3-methylhistidine and of total nitrogen into urine was measured. Two control groups were used: rats with total restriction of food and rats which were fed ad libitum. 2 ml olive-oil given to rats within 12 hours decreased the concentration of alanine, valine, leucine, isoleucine. Whereas food restriction increased the excretion of 3-methylhistidine into urine and the blood concentration of leucine, isoleucine, valine, tyrosine, phenylalanine, threonine, and glutamine, the oil-fed rats showed no increase of amino acid levels in plasma and no increase of 3-methylhistidine excretion into urine. These experiments suggest that lipid application inhibits proteolysis in muscle, and thus diminishes the amino acid levels in blood.

Amino Acids↗
PubMed1983

Immunohistochemical localization of two proteinases in skeletal muscle.

Immunohistochemical localizations of cytosolic and myofibrillar proteinases revealed a different myofiber locale for each enzyme in the rat. Although the cytosolic proteinase was most pronounced in mast cells within soleus and extensor digitorum longus (EDL) muscles, certain fibers of the EDL were also positive. The myofibrillar proteinase, on the other hand, appeared to be present in interstitial spaces between muscle fibers in the EDL but conversely present in some fibers of the soleus muscle.

Animals↗
PubMed1983

Influence of bradykinin on glucose uptake and metabolism studied in isolated cardiac myocytes and isolated perfused rat hearts.

To study whether bradykinin influences myocardial glucose metabolism as suggested for skeletal muscle, we studied the effect of bradykinin on myocardial glucose transport using isolated cardiac cells and on glucose metabolism using the isolated perfused rat heart. In isolated cardiac myocytes bradykinin alone had no influence on the initial velocity of basal glucose transport nor on the sensitivity of the glucose carrier towards stimulation by insulin. By contrast, in isolated perfused hearts bradykinin increased the rate of glucose uptake and oxidation as well as the formation of lactate independently of the action of insulin. In diabetic hearts, neither bradykinin nor insulin alone had a significant influence on myocardial glucose oxidation, however, both hormones together act synergistically to improve glucose oxidation. These data suggest that bradykinin enhanced the nutritional flow across the capillary wall and, thereby, indirectly accelerates the glucose metabolism in the isolated perfused heart. There is no evidence for a direct effect of bradykinin on the rate of glucose transport in the heart.

Animals↗
PubMed1983

Effects of microtubule-disrupting agents on insulin binding and degradation in isolated cardiocytes from adult rat.

Isolated muscle cells from adult rat heart have been used to study the effects of microtubule disruptive drugs on the maintenance of steady-state insulin binding to cardiac insulin receptors. Vinblastine, vincristine and podophyllotoxin significantly inhibited insulin binding (25-50%) in the presence of insulin (10(-8) mol/l). The effect of vinblastine was found to be time- and temperature-dependent and to be dependent on the amount of insulin bound to the cell. In the presence of cycloheximide (0.1 mmol/l) insulin binding decreased by 30%; this effect was found to be additive to the action of vinblastine. Treatment of cells with vinblastine significantly reduced the low-molecular mass material produced by receptor-mediated degradation of insulin. This effect was not additive to that of the lysosomotropic agent chloroquine. The results suggest involvement of microtubules in the intracellular transfer of insulin receptors from and to the plasma membrane.

Animals↗