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Biomedical subjects

H Stam

Publications and source records attributed to H Stam.

At least 73 records · Page 4Linked to original sources
PubMed1986

The effect of the dissolved oxygen concentration and anabolic limitations on the behaviour of Rhizobium ORS571 in chemostat cultures.

Chemostat cultures of Rhizobium ORS571 limited by the supply of oxygen or an anabolic substrate contained poly-beta-hydroxybutyrate (PHB). Low amounts of PHB (about 10%) were present in ammonia- or nitrate-limited cultures; higher amounts were found in Mg++-limited cultures (about 20%) and in oxygen-limited nitrogen-fixing cultures (37%). A method is described to calculate YATP values (g PHB-free biomass . mol-1 ATP) from the Ysucc values (g dry wt . mol-1 succinate) measured. Ysucc and YATP values in cultures limited by the supply of an anabolic substrate and in the oxygen-limited ammonia-assimilating culture were much lower than the values found in the PHB-free succinate-limited cultures. This shows that uncoupling of growth and energy production occurred. Therefore, H2/N2 ratio (mol hydrogen formed per mol nitrogen fixed) in nitrogen-fixing cultures could not be calculated from the comparison of the YATP value found in the nitrogen-fixing culture and the value found in the corresponding ammonia-assimilating culture. Although the optimal dissolved oxygen concentration (d.o.c.) for nitrogen-fixing cultures of Rhizobium ORS571 is 5 or 10 microM, nitrogen-fixing cultures could be obtained up to a d.o.c. of 40 microM. Not only nitrogenase but also hydrogenase was active at this d.o.c. However, accumulation of PHB (10%) may indicate that cultures grown at unfavourable oxygen concentrations (15-40 microM O2) were N-limited rather than energy-limited, which may be the result of partial inactivation or repression of nitrogenase at a higher d.o.c.

Adenosine Triphosphate↗
PubMed1985

Studies on cumene hydroperoxide-induced lipid peroxidation in the isolated perfused rat heart.

In the isolated, perfused rat heart, lipid peroxidation, induced by cumene hydroperoxide (Cum OOH), is accompanied by the release of malondialdehyde (MDA). Using a modified perfusion technique resulting in the separate collection of coronary and interstitial effluent, it can be shown that upon Cum OOH (0.5 mM) perfusion there is an immediate release of MDA in the coronary effluent and a delayed release in the interstitial fluid, indicating the susceptibility and coronary vascular tissue towards free radical-induced lipid peroxidation. Perfusion with Cum OOH leads to an initial increase of the coronary flow and a depressed contractility followed by a cardiac arrest concomitantly with the onset of MDA release in the interstitial fluid. Finally, during prolonged perfusion the coronary flow diminishes and contracture of the heart muscle ('stone heart') develops. These phenomena resemble those occurring during the 'calcium paradox'. Although the contractility diminishes immediately after the perfusion with Cum OOH the tissue ATP level and energy charge (formula; see text) remain constant. From the moment of cardiac arrest the ATP and creatine phosphate levels gradually decrease and the energy charge drops simultaneously with the appearance of MDA in the interstitial fluid. In contrast to the calcium paradox there is no simultaneous increase in the myocardial AMP level. Various mitochondrial enzymes (cytochrome c oxidase, monoamine oxidase, carnitinepalmitoyltransferase I and palmitoyl CoA synthetase) were tested and not affected by Cum OOH perfusion. During the development of contracture after 20 min of Cum OOH perfusion massive contraction band necrosis of cardiac tissue occurs. However, overall protein release is lower when compared with the protein release during the calcium paradox.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗
PubMed1985

Regulation of lipases involved in the supply of substrate fatty acids for the heart.

Evidence is presented that all lipase activities present in the vascular and myocardial tissue from rat heart are regulated by product inhibition. Lipoprotein lipase activity, which plays a role in the uptake of circulating triglycerides, is determined by its reaction products, e.g. fatty acids and, predominantly, monoglycerides. Tissue acid and neutral lipase activities are regulated by product fatty acids and their coenzyme A (CoA) and carnitine ester derivatives. The order of potency is palmitoyl CoA approximately palmitoyl carnitine greater than palmitate for neutral lipase and palmitoyl carnitine greater than palmitoyl CoA palmitate for acid lipase activity. Product inhibition of extracellular and intracellular lipolytic processes warrants a close coupling between the supply of substrate fatty acids and the rate of fatty acid oxidation as determined by cardiac contractile activity. None of the lipases studied was directly affected by catabolic hormones (norepinephrine, glucagon) or their intracellular second messengers (cyclic AMP, protein kinase, Ca2+, calmodulin).

Animals↗
PubMed1984

Effects of hormones, amino acids and specific inhibitors on rat heart heparin-releasable lipoprotein lipase and tissue neutral lipase activities during long-term perfusion.

Rat hearts were perfused for long periods in the presence of 14C-labeled amino acids. From these hearts, postheparin-effluent and a tissue homogenate containing lipoprotein lipase and neutral lipase, respectively, were derived. Lipolytic activity and 14C-labeled protein in both preparations were characterized by affinity chromatography, immunoprecipitation and SDS-polyacrylamide gel electrophoresis. Lipase activity and 14C-labeled protein co-eluted from heparin-Sepharose 4B at 1.2 M NaCl and were inhibited and precipitated by preincubation with anti-lipoprotein lipase gamma-globulins. Gel electrophoresis of both preparations showed the presence of 14C-labeled protein with a molecular weight of 35 000. These data strongly suggest similarity between lipoprotein lipase and neutral lipase and their possible precursor-product relationship and indicate that during perfusion continuous synthesis, secretion and vascular binding of lipase molecules occur. Cycloheximide perfusion induced a dramatic decrease of lipoprotein lipase and neutral lipase activity, indicating a half-life of less than 90 min for both enzymes. Tunicamycin present during perfusion also induced a drop in lipoprotein lipase and tissue neutral lipase activity, indicating that glycosylation is necessary for secretion of lipoprotein lipase. Long-term perfusion of rat hearts in the presence of norepinephrine, glucagon or tyrosine leads to reciprocal alterations in lipoprotein lipase and neutral lipase activities, i.e., lipoprotein lipase activity increased and neutral lipase activity decreased, whereas total lipase activity (lipoprotein lipase + neutral lipase) remained unaltered. During perfusion in the presence of insulin, no net change in lipase activities was observed. Also, insulin did not affect the glucagon-induced inverse effects on either lipase activity. The reciprocal changes in lipase activities occurring during norepinephrine perfusion were hampered by colchicine and propranolol, pointing towards beta-receptor and microtubular mediation of tissue lipase processing and endothelial binding. Our data suggest that the tissue flux and vascular binding of lipase protein may be important sites of hormonal regulation of lipoprotein lipase homeostasis.

Amino Acids↗
PubMed1984

Hydrogen oxidation and nitrogen fixation in rhizobia, with special attention focused on strain ORS 571.

In this survey we describe the influence of hydrogen oxidation on the physiology of Rhizobium ORS 571. The presence of hydrogen is required for the synthesis of hydrogenase. Carbon substrates do not repress the synthesis of hydrogenase. The respiratory system contains cytrochromes of the b- and c-type. Cytochrome alpha 600 is present after growth at high oxygen tensions. The nature of the terminal oxidases functioning at low oxygen tensions has not been established yet----H+/O values with endogenous substrates are between 6 and 7. The results show the presence of two phosphorylation sites: site 1 (ATP/2e = 1.0) and site 2(ATP/2e = 1.33). By measuring molar growth yields it has been demonstrated that carbon-limited, nitrogen-fixing cultures obtain additional ATP from hydrogen oxidation, and that site 2 of oxidative phosphorylation is passed during hydrogen oxidation. A method is described to calculate ATP/N2 values (the total amount of ATP used by nitrogenase during the fixation of 1 mol N2) and H2/N2 ratios (mol hydrogen formed per mol N2 fixed) in aerobic organisms. For Rhizobium ORS 571 the ATP/N2 value is about 40 and the H2/N2 ratio is between 5 and 7.5. Cells obtained from oxygen-limited nitrogen-fixing cultures contain 30-40% poly-beta-hydroxybutyrate, which explains the high molar growth yields found. Hydrogen has not been detected in the effluent gas of these cultures, which may point to reoxidation of the hydrogen formed at nitrogen fixation. Calculations show that the effect of hydrogen reoxidation on the efficiency of nitrogen fixation (g N fixed X mol-1 substrate converted) is not very large and that the actual H2/N2 ratio is of much more importance. After addition of hydrogen to succinate-limited, ammonia-assimilating cultures, an initial increase of the Ysuccinate value (g dry wt X mol-1 succinate) is followed by a gradual decrease. This is accompanied by a large decrease of the YO2 value, and an increased permeability of the cytoplasmic membrane to protons. The results may be explained by a transition of the culture from an energy-limited state to a carbon-limited state.

Adenosine Triphosphate↗
PubMed1984

Effects of hormones, fasting and diabetes on triglyceride lipase activities in rat heart and liver.

Male rats were fasted for 3 days, subjected to streptozotocin-diabetes or injected with L-thyroxine, Kenacort-A40 (corticosteroid) and Synacthen (ACTH). Cardiac heparin-releasable lipoprotein lipase (LPL) activity was increased after fasting, experimental diabetes and all hormone treatments. Cardiac neutral lipase activity was decreased during diabetes and enhanced in the fasted state and by L-thyroxine, corticosteroid and ACTH administration. The close correlation between vascular LPL and tissue neutral lipase with cardiac triglyceride content is in agreement with the contention that tissue neutral lipase is similar to LPL (Hülsmann, Stam and Breeman 1982). Myocardial acid lipase activity was reduced during diabetes and L-thyroxine treatment, increased during fasting and corticosteroid administration and not affected by short-term ACTH treatment. Hepatic acid lipase activity was increased during fasting, diabetes and by L-thyroxine and reduced after corticosteroid and ACTH treatment. The alkaline liver lipase activity was depressed by fasting, experimental diabetes, corticosteroid and ACTH treatment, whereas L-thyroxine induced a slight increase in enzyme activity. The possible mechanism underlying the observed changes in acid, neutral, alkaline, and LPL activities in heart and liver are discussed.

Adrenocorticotropic Hormone↗
PubMed1983

Comparison of heparin-releasable lipase and tissue neutral lipase activity of rat heart.

The alkaline, heparin-releasable lipoprotein lipase (LPL) activity of isolated, perfused rat hearts was compared with the residual neutral lipase (NL) activity detectable in the post nuclear supernatant (PNS) from a tissue homogenate. Both enzyme activities were increased by serum, heparin and apolipoprotein CII, inhibited by high salt concentrations and by immunotitration with an anti-LPL gamma-globulin fraction. Protamine sulphate from saline liver inhibited LPL activity and the NL activity only in the absence of serum. Incubation of the PNS NL under classic conditions of hormonal stimulation (by phosphorylation) did not alter its activity and upon short-term preperfusion of the hearts with norepinephrine and glucagon also unchanged LPL and NL activities were measured. Our experiments are indicative of a possible similarity between vascular LPL and tissue NL and show that the lipase activities are not sensitive towards hormonal stimulation.

Animals↗
PubMed1982

The effect of excess (acyl) carnitine on lipid metabolism in rat heart.

During Langendorff perfusion of rat hearts with Intralipid, the resulting fat accumulation in the hearts can be inhibited by the addition of 5 mM L-carnitine to the perfusion medium. The mechanism of this phenomenon is probably the inhibition of lipid accumulation in the heart by acylcarnitine rather than stimulation of fatty acid oxidation by excess carnitine addition. Palmitoylcarnitine was found to stimulate trioleoylglycerol hydrolysis at neutral pH in heart homogenates, when it was tested in the presence of relatively much protein. At higher palmitoylcarnitine: protein ratios, however, lipolysis was inhibited. Inhibition of lipolysis was also observed in lipid-enriched hearts during retrograde perfusion by the addition of 5 mM carnitine suggesting that also in intact heart long-chain acylcarnitine excess may inhibit lipolytic activity.

Animals↗
PubMed1982

Intracellular origin and regulation of endogenous lipolysis in rat heart.

The rate of glycerol release from isolated, perfused rat hearts was used as an index for endogenous lipolysis. Pharmacological and metabolic interventions were performed in order to obtain information about the intracellular site of action and regulation of tissue triglyceride (TG) hydrolysis in heart. It proved that endogenous lipolysis probably is of lysosomal origin. The activity of tissue lipolysis is dependent on the amount of stored TG and on the contractile status of the heart and is subject to feedback inhibition by production of fatty acids. Evidence is presented that Ca2+ plays an important role in the regulation and hormonal modification of lipolysis since all mechanisms inducing alterations in Ca2+ homeostasis influence myocardial lipolysis. Our experimental data and current knowledge are discussed in the light of a new hypothesis which relates intracellular Ca2+ and the rate of fatty acid utilization to the activity (activities) of tissue lipase(s). It is proposed that inhibition of endogenous lipolysis may be the main mechanism of action of antiarrhythmic agents (lidocaine, quinidine, phenothiazines).

Animals↗
PubMed1982

Dual localization of lipoprotein lipase in rat heart. Its relationship to chylomicron degradation.

Rat hearts were perfused retrogradely using a modified technique that allows the separate collection of coronary (Qrv) and interstitial (Qi) effluents. Evidence is presented that Qrv contains products from the coronary vasculature and that Qi contains products arising from cardiac myocytes. Heparin perfusion of rat hearts led to a release of lipolytic activity in Qrv and Qi which was characterized as lipoprotein lipase (LPL). The relative amounts of LPL released in Qrv and Qi were dependent on the feeding condition of the rat. A high LPL activity was recovered from Qrv of fasted rats, and Qi was high in LPL during feeding. On perfusion of hearts with [3H]cholesterol-labeled chylomicrons, the tissue uptake of cholesterol was highest in the fasted state, whereas release of radioactivity in Qi was predominant in the fed state. This radioactivity in Qi appeared to be associated with chylomicron degradation products (remnants and surface fragments). Our experiments indicate that cholesterol uptake during chylomicron breakdown is inhibited in the fed state, and the relationship between myocyte LPL activity and interstitial formation of chylomicron degradation products suggests a role for the myocyte LPL in lipoprotein metabolism.

Animals↗