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Biomedical subjects

H Löw

Publications and source records attributed to H Löw.

At least 55 records · Page 3Linked to original sources
PubMed1985

Effects of fasting and refeeding on the activity of hepatic glucose-6-phosphatase in rats.

The activities of glucose-6-phosphate hydrolase and glucose-6-phosphate translocase were determined in rats fasted for 1-3 days and in animals fasted for one day and then either refed with mixed pellet or given oral or intraperitoneal glucose. The assay was based on the colorimetric measurement of the released inorganic phosphate. Fasting over 24 h significantly increased both the translocase and the hydrolase activity of glucose-6-phosphatase. These parameters showed a further increase when rats were fasted for another 24 h. In animals fasted for 24 h and then refed with standardized pellet diet, a progressive fall of enzyme activity was noticed. However, even 72 h of refeeding did not lead to complete normalization. Glucose given orally or intraperitoneally also suppressed the enzyme activity, although the effect was somewhat delayed. As expected, in fasting rats glucose and insulin levels were significantly decreased. Normoglycaemia was established after just 24 h, regardless of refeeding with pellets or with glucose. The former group exhibited hyper- and the latter hypo-insulinaemic pattern. We speculate that augmented activity of hepatic glucose-6-phosphatase during fasting stimulates the metabolism of glucose through the glucose cycle and is thereby at least partially responsible for insulin resistance accompanying the fasting state.

Administration, Oral↗
PubMed1984

Transplasma membrane redox stimulates HeLa cell growth.

Impermeable ferricyanide stimulates the growth of HeLa cells in absence of fetal bovine serum or other growth factors. A series of impermeable oxidants with redox potentials down to -125 mV stimulate equivalent growth. All of these oxidants are reduced by the transplasma membrane electron transport system. Oxidants with redox potentials below -175 mV are not reduced by the transmembrane electron transport and do not stimulate growth. Insulin which stimulates growth in absence of serum also stimulates transmembrane ferricyanide reduction. Ferricyanide increases growth in presence of insulin. Antitumor drugs, which inhibit HeLa cell growth, inhibit the transplasma membrane redox system. Transplasma membrane electron transport is accompanied by proton release from HeLa cells.

Cell Division↗
PubMed1984

Properties and regulation of a trans-plasma membrane redox system of perfused rat heart.

Ferricyanide was reduced to ferrocyanide by the perfused rat heart at a linear rate of 78 nmol/min per g of heart (non-recirculating mode). Ferricyanide was not taken up by the heart and ferrocyanide oxidation was minimal (3 nmol/min per g of heart). Perfusate samples from hearts perfused without ferricyanide did not reduce ferricyanide. A single high-affinity site (apparent Km = 22 microM) appeared to be responsible for the reduction. Perfusion of the heart with physiological medium containing 0.5 mM ferricyanide did not alter contractility, biochemical parameters or energy status of the heart. Perfusate flow rate and perfusate oxygen concentration exerted opposing effects on the rate of ferricyanide reduction. A net decreased reduction rate resulted from a decreased perfusion flow rate. Thus, the rate of supply of ferricyanide dominated over the stimulatory effect of oxygen restriction; the latter effect only becoming apparent when the oxygen concentration was lowered at a high perfusate flow rate. Whereas glucose (5 mM) increased the rate of ferricyanide reduction, pyruvate (2 mM), acetate (2 mM), lactate (2 mM) and 3-hydroxybutyrate (2 mM) each had no effect. Insulin (3 nM), glucagon (0.5 microM), dibutyryl cyclic AMP (0.1 mM) and the beta-adrenergic agonist ritodrine (10 microM) also had no effect, however, the alpha 1-adrenergic agonist, methoxamine (10 microM), produced a net increase in the rate of ferricyanide reduction. It is concluded that a trans-plasma membrane electron efflux occurs in perfused rat heart that is sensitive to oxygen supply, glucose, perfusion flow rate, and the alpha-adrenergic agonist methoxamine.

Adenosine Diphosphate↗
PubMed1984

A transmembranous NADH-dehydrogenase in human erythrocyte membranes.

Evidence is presented for a transmembranous NADH-dehydrogenase in human erythrocyte plasma membrane. We suggest that this enzyme is responsible for the ferricyanide reduction by intact cells. This NADH-dehydrogenase is distinctly different from the NADH-cytochrome b5 reductase on the cytoplasmic side of the membrane. Pretreatment of erythrocytes with the nonpenetrating inhibitor diazobenzene sulfonate (DABS) results in a 35% loss of NADH-ferricyanide reductase activity in the isolated plasma membrane. Since NADH and ferricyanide are both impermeable, the transmembrane enzyme can only be assayed in open membrane sheets with both surfaces exposed, and not in closed vesicles. The transmembrane dehydrogenase has affinity constants of 90 microM for NADH and 125 microM for ferricyanide. It is inhibited by p-chloromercuribenzoate, bathophenanthroline sulfonate, and chlorpromazine.

Cytochrome Reductases↗
PubMed1984

Properties of a transplasma membrane electron transport system in HeLa cells.

A transmembrane electron transport system has been studied in HeLa cells using an external impermeable oxidant, ferricyanide. Reduction of ferricyanide by HeLa cells shows biphasic kinetics with a rate up to 500 nmoles/min/g w.w. (wet weight) for the fast phase and half of this rate for the slow phase. The apparent Km is 0.125 mM for the fast rate and 0.24 mM for the slow rate. The rate of reduction is proportional to cell concentration. Inhibition of the rate by glycolysis inhibitors indicates the reduction is dependent on glycolysis, which contributes the cytoplasmic electron donor NADH. Ferricyanide reduction is shown to take place on the outside of cells for it is affected by external pH and agents which react with the external surface. Ferricyanide reduction is accompanied by proton release from the cells. For each mole of ferricyanide reduced, 2.3 moles of protons are released. It is, therefore, concluded that a transmembrane redox system in HeLa cells is coupled to proton gradient generation across the membrane. We propose that this redox system may be an energy source for control of membrane function in HeLa cells. The promotion of cell growth by ferricyanide (0.33-0.1 mM), which can partially replace serum as a growth factor, strongly supports this hypothesis.

Cell Division↗
PubMed1984

Inhibition of plasma membrane NADH dehydrogenase by adriamycin and related anthracycline antibiotics.

Doxorubicin (adriamycin) is cytotoxic to cells, but the biochemical basis for this effect is unknown, although intercalation with DNA has been proposed This study suggests that the cytotoxicity of this drug may be due to inhibition of the plasma membrane redox system, which is involved in the control of cellular growth. Concentrations between 10(-6) - 10(-7) M adriamycin inhibit plasma membrane redox reactions greater than 50%. AD32, a form of adriamycin which does not intercalate with DNA, but is cytotoxic, also inhibits the plasma membrane redox system. Thus, the cytotoxic effects of adriamycin, which limit its use as a drug, may be based on the inhibition of a transplasma membrane dehydrogenase involved in a plasma membrane redox system.

Animals↗
PubMed1983

Transformed liver cells have modified transplasma membrane redox activity which is sensitive to adriamycin.

Electron transport across the plasma membrane is found in all cells which have been tested. This activity has been implicated in control of cellular growth, transport and hormone response. In virus transformed cells and tumor cells we find the activity is decreased and becomes sensitive to the antitumor drug adriamycin. Inhibition of transmembrane redox by adriamycin parallels cytoxicity to transformed cells.

Animals↗
PubMed1983

Heterogeneity of immunoreactive calcitonin in human milk.

Immunoreactive calcitonin (ICT) has been detected in human milk by radioimmunoassay (RIA), using antibodies raised against synthetic human calcitonin (hCT). The level of ICT was 10-40 times higher than the reference level of human serum. Gel chromatography of human milk disclosed a molecular weight heterogeneity of ICT, with at least two forms larger than the monomer (Mr greater than 70000 and 30000 approximately). The 30000 peak constituted the major fraction of ICT. No detectable amount of ICT was coeluted with [125I]CT. Reduction with disulphide cleaving agents, denaturation or acidification did not alter the gel chromatographic properties of ICT, while tryptic digestion caused partial degradation of ICT and formation of new ICT molecules with an approximate molecular weight of 6000.

Calcitonin↗
PubMed1983

NADH-monodehydroascorbate reductase in human erythrocyte membranes.

Enzymatic activity of NADH-monodehydroascorbate reductase could be observed in red blood cell membranes. This activity was latent in right side out as well as inside out vesicles. Apart from this latency addition of certain detergents led to activation of the enzyme also in open membrane preparations. The enzyme was inhibited by metal chelators, and displayed a very low apparent Michaelis constant. Monodehydroascorbate is a candidate for the natural electron acceptor of the transmembrane NADH-oxido-reductase. The activation by detergent may be due to enhancement of lipid fluidity or to exposure of a lipophilic substrate binding site.

Erythrocyte Membrane↗
PubMed1982

Insulin control of a transplasma membrane NADH dehydrogenase in erythrocyte membranes.

A study of NADH ferricyanide reductase activity in oriented vesicles or open ghosts of human and porcine erythrocytes shows that the dehydrogenase activity can have three types of orientation in the membrane. There is activity which responds only to acceptors and NADH exclusively on the inside face, or exclusively on the outer surface. There is also activity which requires exposure of both sides of the membrane and thus is transmembranous. The transmembrane activity is inhibited by insulin, whereas the internal and external enzymes do not respond to insulin. The transmembrane dehydrogenase can be a basis for proton transport in the plasma membrane.

Animals↗
PubMed1982

Transmembrane ferricyanide reduction by cells of the yeast Saccharomyces cerevisiae.

Both respiratory-competent and respiratory-deficient yeast cells reduce external ferricyanide. The reduction is stimulated by ethanol and inhibited by the alcohol dehydrogenase inhibitor, pyrazole. The reduction of ferricyanide is not inhibited by inhibitors of mitochondrial or microsomal ferricyanide reduction. Cells in exponential-phase growth show a much higher rate of ferricyanide reduction. The reduction of ferricyanide is accompanied by increased release of protons by the yeast cells. We propose that the ferricyanide reduction is carried out by a transmembrane NADH dehydrogenase.

Ferricyanides↗
PubMed1982

Clinical characteristics of 18-year-old men with elevated blood pressure.

Twenty "hypertensive" 18-year-old men (systolic BP greater than or equal to 146 and/or diastolic BP greater than or equal to 90 mmHg) from the screening examinations of a military draught bureau were compared with 17 normotensive (systolic BP 124-131) and 12 hypotensive (systolic BP 100-106) subjects. The hypertensive subjects were on average taller, showed more often ECG evidence of sympathoadrenomedullary overactivity, tended to excrete more adrenaline in the urine during a standardized psychological stress test, had higher serum levels of sodium and potassium and reported more frequently family prevalence of hypertension than the normotensives and hypotensives. Non-participating subjects without verified hypertension had higher mean relative weight than any of the study groups. Only one hypertensive subject showed dilated pulmonary vessels on chest X-ray and borderline evidence of mild left ventricular hypertrophy. None of the hypertensive subjects showed evidence of decreased glomerular filtration rate or endocrine disorder. The subjects in both comparison groups showed frequently ECG evidence of parasympathetic activity. The hypotensive group had a lower average relative body weight than the other groups.

Adolescent↗
PubMed1982

Urinary cyclic AMP corrected for glomerular filtration rate in the differential diagnosis of hypercalcemia.

To evaluate the usefulness of urinary cyclic AMP (U-cAMP) expressed as nmol/100 ml glomerulus filtrate (GF) when discriminating various hypercalcemic states, we studied 99 patients. Patients with primary hyperparathyroidism (PHPT) showed a positive correlation between individual S-calcium levels and U-cAMP, nmol/100 ml GF (females r=0.49, n=40, p less than 0.01 and males r=0.91, n=7 p less than 0.001). There was also a correlation between U-cAMP, nmol/100 ml GF, and the weight of the adenomas (females r=0.36, n=32, p less than 0.05) and males r=0.79, n=6, p less than 0.05). Patients with PHPT and normal renal function excreted more U-cAMP than controls, 6.0 +/- 1.6 versus 4.3 +/- 1.0 nmol/100 ml GF (mean +/- SD). Of 47 patients with PHPT and normal renal function, 29 showed values below the upper normal limit, 6.3 nmol/100 ml GF (mean +/-2 SD), of the control group; the overlap was 62%. When U-cAMP was expressed as mumol/24 hours, the overlap was 40/47 (85%) and, when expressed as mumol/g creatinine, 31/47 (66%). Three patients with sarcoidosis and two with malignancies and hypercalcemia showed excretory values of U-cAMP, nmol/100 ml GF, above the upper normal limit. Patients with acromegaly or prolactinoma showed normal values of U-cAMP, nmol/100 ml GF. The present data indicate that all three types of determinations of urinary cAMP based on 24 hour urine collections are of little value in the differential diagnosis of hypercalcemic states.

Acromegaly↗
PubMed1981

Evidence for the extracellular reduction of ferricyanide by rat liver. A trans-plasma membrane redox system.

1. Reduction of ferricyanide by the isolated perfused rat liver and by isolated rat hepatocytes was studied. 2. Ferricyanide was reduced to ferrocyanide by the perfused liver at a linear rate of 0.22mumol/min per g of liver. Ferricyanide was not taken up by the liver and the perfusate concentration of ferricyanide+ferrocyanide remained constant throughout the perfusion. Perfusate samples from livers perfused without ferricyanide did not reduce ferricyanide. 3. Isolated hepatocytes reduced ferricyanide in a biphasic manner. The initial rate of 2.3mumol/min per g of cells proceeded for approx. 3min and derived from low-affinity sites (apparent K(m)>1.3mm). The secondary rate of 0.29mumol/min per g of cells was maintained for the remainder of the incubation and derived from higher affinity sites (apparent K(m)0.13mm). Disruption of the cells resulted in an increase in the low-affinity rate and a decrease in the high-affinity rate. 4. Ferrocyanide was oxidized by isolated hepatocytes but not by perfused liver. The apparent K(m) for ferrocyanide oxidation by hepatocytes was 1.3mm. 5. Oxidized cytochrome c was reduced by isolated hepatocytes in the presence of 1mm-KCN but at a rate less than that of the reduction of ferricyanide. 6. Properties of the ferricyanide-reducing activities of intact hepatocytes and the perfused liver were examined. The low-affinity rate, present only in cell and broken cell preparations, was inhibited by 1mum-rotenone and 0.5mm-ferrocyanide, and stimulated by 0.1mm-KCN. The mitochondrial substrate, succinate, also stimulated this rate. The perfused liver showed only a high-affinity activity for ferricyanide reduction. This activity was also present in liver cells and was unaffected by rotenone, antimycin A, KCN, NaN(3), or p-hydroxymercuribenzoate but was inhibited by 2.6mm-CaCl(2), 2-heptyl-4-hydroxyquinoline-N-oxide and ferrocyanide. Overall, these results are consistent with the occurrence of a trans-plasma membrane redox system of liver that reduces extracellular ferricyanide to ferrocyanide. The reduction process shows properties which are similar to that of the NADH:ferricyanide oxidoreductase found in isolated liver plasma membranes but different from that of mitochondria.

Animals↗
PubMed1981

Role of aerobic conditions in the control of cell proliferation.

Our experiments demonstrate that proliferation of human lymphocytes as well as fibroblasts is inhibited by oxygen. It is not a toxic effect and it has been possible to find an intermediary link in intracellular glycolysis, oxidate metabolism, or macromolecule synthesis. Accessory cells may reduce the inhibitory action of oxygen, thereby exerting an influence on the growth rate. In view of recent hypotheses on the mediation of hormone effects via a membrane dehydrogenase system our results may indicate that also the mitotic activation is dependent on the redox state of the membrane for the function of a proton gradient across the plasma membrane itself, delivering energy for glucose and amino acid transport.

Aerobiosis↗