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Biomedical subjects

H Stam

Publications and source records attributed to H Stam.

At least 55 records · Page 3Linked to original sources
PubMed1990

Properties of phosphatidate phosphohydrolase and diacylglycerol acyltransferase activities in the isolated rat heart. Effect of glucagon, ischaemia and diabetes.

Myocardial triacylglycerol hydrolysis is subject to product inhibition. After hydrolysis of endogenous triacylglycerols, the main proportion of the liberated fatty acids is re-esterified to triacylglycerol, indicating the importance of fatty acid re-esterification in the regulation of myocardial triacylglycerol homoeostasis. Therefore, we characterized phosphatidate phosphohydrolase (PAP) and diacylglycerol acyltransferase (DGAT) activities, enzymes catalysing the final steps in the re-esterification of fatty acids to triacylglycerols in the isolated rat heart. The PAP activity was mainly recovered in the microsomal and soluble cell fractions, with an apparent Km of 0.14 mM for both the microsomal and the soluble enzyme. PAP was stimulated by Mg2+ and oleic acid. Oleic acid, like a high concentration of KCl, stimulated the translocation of PAP activity from the soluble to the particulate (microsomal) fraction. Myocardial DGAT had an apparent Km of 3.8 microM and was predominantly recovered in the particulate (microsomal) fraction. Both enzyme activities were significantly increased after acute streptozotocin-induced diabetes, PAP from 15.6 +/- 1.1 to 28.1 +/- 3.6 m-units/g wet wt. (P less than 0.01) and DGAT from 2.23 +/- 0.11 to 3.01 +/- 0.11 m-units/g wet wt. (P less than 0.01). In contrast with diabetes, low-flow ischaemia during 30 min did not affect PAP and DGAT activity in rat hearts. Perfusion with glucagon (0.1 microM) during 30 min did not affect total PAP activity, but changed the subcellular distribution. More PAP activity was recovered in the particulate fraction. DGAT activity was lowered by glucagon treatment from 0.37 +/- 0.03 to 0.23 +/- 0.02 m-unit/mg of microsomal protein (P less than 0.05). The role of PAP and DGAT activity and PAP distribution in the myocardial glucose/fatty acid cycle is discussed.

Acyltransferases↗
PubMed1990

Design and validation of an indicator gas injector for multiple gas washout tests in mechanically ventilated patients.

A device to produce a stepwise indicator gas fraction variation to initiate a washout test in mechanically ventilated patients is described. The device, which can be used in conjunction with the commonly used Siemens-Elema series 900 ventilators, is based on simple, off-the-shelf technology. It features the simultaneous use of two indicator gases (so that the influence of diffusion processes in the gas exchange to the patient can be measured) and maintains a nearly constant FIO2 during a washout procedure. With this indicator gas injector, the transition time of the indicator gas fraction at the beginning of a washout proved to be short enough to detect ventilation inhomogeneity by visual inspection of the washout curves. Functional residual capacity measurements using this device are presented on a test lung with known volume, on healthy volunteers, and on critically ill patients.

Adolescent↗
PubMed1990

Relationship between airway obstruction, desaturation during exercise and nocturnal hypoxaemia in cystic fibrosis patients.

We measured pulmonary function, responses to exercise and oxygen saturation (So2) at rest, and also before and during sleep in 24 patients with cystic fibrosis in a varying degree of severity. The pulmonary function indices analysed were forced expiratory volume in one second (FEV1), total lung capacity (TLC), measured by body plethysmography (TLC box) and Helium dilution (TLC He), residual volume measured by body plethysmography (RV) and the amount of trapped air (TA = TLC box-TLC He). The exercise variables included symptom limited maximal oxygen uptake (Vo2max), maximum minute ventilation (VEmax) and So2, at rest in sitting position and during maximal exercise. So2 was measured by ear oximetry. The lowest mean So2 obtained in two consecutive nights over a period of 1 hour was taken as the indicator of nocturnal oxygen saturation. A high correlation existed between resting supine and sitting So2, and the degree of nocturnal hypoxaemia (0.84 and 0.76, respectively). Highly significant correlations existed also for the indices of airway obstruction, Vo2 max and lowest So2 at exercise versus the nocturnal lowest hourly mean So2. From all variables a resting So2 in the sitting position lower than 94% appeared to be most predictive of nocturnal desaturation and indicates a risk of nocturnal hypoxaemia in patients with cystic fibrosis.

Adolescent↗
PubMed1989

Effects of dietary protein content on weaning from the ventilator.

The effect of enteral nutrition with different protein contents on metabolic and ventilatory variables during weaning from the ventilator was studied in 10 mechanically ventilated patients as indication of the effect of protein on the ventilatory drive. Resting energy expenditure (R.E.E.) was assessed in the post-absorptive state and 2 enteral regimens both with a fat and carbohydrate content 1.25 times R.E.E. but with a moderate (190 mg N/kg/24 h) and high (260 mgN/kg/24 h) protein content were given to the patients in random order. Minute ventilation (V(E)), CO2-production (VCO2), O2-consumption (VO2) and arterial blood-gases were obtained during mechanical ventilation and weaning. Compared with post-absorptive state, both intakes gave significant increases in VCO2 during mechanical ventilation; the VCO2 values were equal for both regimens before the start of the weaning procedures. High protein intake was associated with significantly higher VCO2 during weaning and smaller increases in paCO2 from mechanical ventilation to the end of the weaning-period, compared with the moderate protein intake. This result is in agreement with studies in which an infusion of amino-acids in spontaneous breathing healthy volunteers increased ventilatory sensitivity to CO2. For mechanically ventilated patients high protein nutrition may be beneficial in enhancing weaning from the ventilator.

Journal Article↗
PubMed1989

Endothelial lesions, dietary composition and lipid peroxidation.

The vascular endothelium can be regarded as a widely distributed organ with a pluripotent function in homeostasis and lipoprotein metabolism. There is now increasing evidence that the vascular endothelium is susceptible to oxygen radicals (oxidative stress). These radical molecules are capable of degrading the polyunsaturated acyl chains of membrane phospholipids (lipid peroxidation), hereby inducing pathologic changes in the underlying tissue. Since the fatty acid composition of our diet is reflected in the composition of cellular membranes, it is conceivable that their may be a relation between the dietary fatty acids and the tissue (endothelial) susceptibility towards lipid peroxidation. In addition, the occurrence of dietary antioxidant molecules (e.g., vitamin E) and trace elements (Se) may be important denominators of tissue protection against peroxidative processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Metabolic and respiratory effects of enteral nutrition in patients during mechanical ventilation.

The effect of enteral feeding on O2-consumption (VO2) and CO2-production (VCO2) was studied in 9 ventilator-dependent patients, who were in a stable condition without signs of hypermetabolism. Resting energy expenditure (REE) in postabsorptive state was assessed and enteral feeding was started by continuous drip (480 kcal carbohydrate, 360 kcal vegetable fat and 160 kcal milkprotein: 6.4 g Nitrogen/1000 ml). Patients were given a moderate and a high caloric intake: 1.5 and 2.0 times REE. VO2 and VCO2 were measured for a 24 h period, beginning 7 h after the start of the dietary intake. Significant greater increases in VO2, VCO2 and RQ were found during high caloric intake compared with the moderate caloric intake. VO2, VCO2 and arterial blood-gases were measured in 4 patients during weaning from the ventilator. The increase in VCO2 induced by the high caloric feeding resulted in a rise in arterial CO2 tension (PaCO2) and respiratory distress. High caloric enteral nutrition can cause a significant increase in VCO2 inducing respiratory distress during weaning from the ventilator in patients with limited pulmonary reserves. Moderate caloric nutrition will be preferable to these patients in order to facilitate the weaning.

Adult↗
PubMed1988

Exercise responses in patients with an enzyme deficiency in the mitochondrial respiratory chain.

Responses to exercise were obtained in six patients with a biochemically diagnosed enzyme deficiency at the level of NADH-CoQ reductase. The responses were compared with those of a control group, consisting of fourteen patients with inexplicable dyspnoea or muscle pain during exercise, for which no firm diagnosis could be established and of which the exercise responses were in the normal range. Metabolic, ventilatory and cardiological variables such as oxygen uptake (VO2), minute ventilation (VE), respiratory exchange ratio (R), heart rate (HR) and difference in blood lactate or base-excess (BE) between rest and maximal workload were measured during cycle ergometry from samples obtained in the last minutes of four minute periods, in which the load increased stepwise by 30 W per four minutes. The threshold of lactate metabolism (Tlact) was assumed to be equal to the threshold determined both by the VO2 at which the VE versus VO2 response started to deviate from a straight line and the ventilatory equivalent for oxygen (VE/VO2) showed a minimum (Tvent), Tvent was estimated from the mean of these values, obtained by linear and parabolic regression analysis respectively. In the patient group, mean values for symptom limited maximal VO2 (VO2,max,sl; % of VO2,max,ref), Tvent (% of VO2,max,ref) and R at maximal workload were 43, 17 and 1.23 against 85, 47 and 1.06 for the same variables in the control group, respectively. The differences were highly significant (p less than 0.001; p less than 0.005 for mean R difference). Mean maximal HR and mean change in blood lactate or BE were not significantly different in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Substrates for energy metabolism in the heart: the role of the interstitial compartment.

Evidence is presented that, as in cardiomyocytes, vascular endothelial cells use fatty acids, in addition to glucose, as a respiratory fuel. Attention is focused on the cardiac interstitium, lined by vascular cells and cardiomyocytes, which may be enriched with metabolic products from these cells. Also, certain proteins are present in the interstitial fluid (Qi) such as plasma proteins and fatty acid binding protein (FABP). However, the concentration of FABP is so low in Qi that albumin is more important to shuttle long chain fatty acids in the interstitial fluid between cardiomyocytes and the vascular compartment. Under hypoxic conditions (hypo)xanthine, lactate and fatty acids may be expected to accumulate in the interstitium, as well as proteins from adjacent cells, such as xanthine oxidase from endothelial cells. This enzyme, acting upon the elevated level of (hypo)xanthine, giving rise to O2-., may be involved in the damage of the ischaemic heart. The significance of the interstitium in ischaemia and in fibrosis following long standing cardiac lipidosis is briefly discussed, as well as the possible mechanisms involved in fatty acid transport in the heart.

Animals↗
PubMed1987

Lipid and carbohydrate metabolism in the ischaemic heart.

Ischaemia has profound effects on myocardial metabolism and cell function in general. High energy phosphate and glycogen stores are depleted. Lactate, inorganic phosphate and hydrogen ions accumulate, exerting negative effects on the initially accelerated glycolytic flux. Fatty acid oxidation is inhibited. The cellular content of lipid intermediates, such as hydroxy-fatty acids, acyl CoA and acylcarnitine, increases in low-flow ischaemia hearts. Non-esterified fatty acid (NEFA) accumulation occurs after 30-60 min ischaemia. Endogenous triacylglycerol and phosphoglyceride turnover is most likely impaired, ultimately resulting in accumulation of lipid droplets in the oxygen deprived cells and in degradation of myocardial membranes. Accumulated lipid substances such as NEFA, acyl CoA, acylcarnitine and lysophosphoglycerides, are likely to be involved in the mechanism underlying ischaemia-induced damage to myocardial cells.

Adenosine Triphosphate↗
PubMed1987

Lipid peroxidation and myocardial ischaemic damage: cause or consequence?

Compelling evidence has been accumulated which indicates that myocardial tissue damage occurring during reperfusion after an ischaemic period may partly be due to the formation of oxygen free radicals and subsequent peroxidative processes. It has been well established that the actual toxicity of free radicals is dependent on the presence of free iron in the heart tissue. Based upon the hypothesis of McCord et al., proposing xanthine oxidase mediated formation of superoxide (O2-.) during the conversion of ATP-breakdown product(s) (hypo)xanthine to urate, we studied whether xanthine oxidase was able to mobilize free iron from the intra- and extracellular iron-binding proteins, ferritin and transferrin. It appeared that there was an O2-.-dependent and O2-.-independent mechanism by which xanthine oxidase could mobilize iron from ferritin while no iron mobilization from transferrin was detectable. The capacity of xanthine oxidase to mobilize iron from ferritin by an O2-.-independent mechanism implies that already during the anoxic/ischaemic period, iron may become available in the tissue which, upon the re-entrance of O2, catalyzes the formation of the very reactive OH radicals. The interaction between endothelial cells and cardiocytes in free radical homeostasis is discussed with the emphasis on the tissue localization of xanthine oxidase. The latter is located in endothelial cells implying an interaction between xanthine oxidase-induced endothelial cells initiated lipid peroxidation and the actual overall myocardial tissue damage.

Animals↗
PubMed1987

Synthesis, storage and degradation of myocardial triglycerides.

In the mammalian myocardium, an active triglyceride synthesis pathway is operating, (re)esterifying activated fatty acids from endogenous or exogenous sources, with the glycolytically derived three-carbon intermediates dihydroxyacetone-phosphate and glycerol-3-phosphate by the so-called Kennedy pathway. The seven enzymes of triglyceride synthesis are membrane bound and located at the sarcoplasmic reticulum. The first enzyme in the glycerol-3-phosphate pathway, glycerol-3-phosphate acyltransferase, is proposed to be rate limiting for triglyceride formation. This microsomal enzyme is regulated by phosphorylation (inactiycation)-dephosphorylation (activation) coupled to the beta-receptor--adenyl cyclase--protein kinase system. Additional regulatory steps in triglyceride formation are the reactions catalyzed by the microsomal phosphatidic acid phosphatase and diglyceride acyltransferase. Intracellular triglycerides occur as free floating cytosolic droplets, membrane-bound particles and lipid-filled lysosomes. No consensus exists about the metabolically active portion of myocardial triglycerides. Various lipases have been proposed to be involved in endogenous lipolysis: the lysosomal acid, microsomal and soluble neutral triglyceride, intracellular lipoprotein lipases and the microsomal di- and monoglyceridase. It has been acknowledged that the bulk of the intracellular neutral lipase represents the precursor of vascular lipoprotein lipase. The presence of a neutral lipase, as distinct from lipoprotein lipase, in the rat heart was recently advocated. Endogenous lipolysis is a hormone-sensitive process. Hormone-sensitivity may involve direct alteration of enzyme activity by protein phosphorylation-dephosphorylation but is also dependent on the removal rate of product fatty acids, since feedback inhibition is a common property of all lipases in the heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Stimulation of myocardial neutral triglyceride lipase activity by adenosine-3':5'-monophosphate: involvement of glycogenolysis.

Endogenous lipolysis can be influenced by various hormones. Hormonal stimulation of endogenous lipolysis in the Langendorff heart was diminished by inhibition of glycogenolysis. Therefore we studied the influence of glycogenolysis on the cAMP-dependent activation of the neutral triglyceride lipase activity using a 40,000 X g post mitochondrial supernatant fraction from rat heart homogenates. In the presence of cAMP and ATP neutral triglyceride lipase activity was stimulated by 40%. This stimulation could not be detected in supernatants from which glycogen was removed after incubation in the presence of amyloglucosidase. Addition of glycogen overcomes this loss of stimulation. The activation of neutral triglyceride lipase by cAMP and ATP was mimicked by glucose plus ATP as well as by glycerol-3-phosphate but not by glyceraldehyde-3-phosphate. Moreover, the cAMP stimulation of neutral triglyceride lipase activity was suppressed by low amounts of palmitoyl-CoA indicating product inhibition of lipase activity. These results indicate that the level of intracellular precursors of fatty acid re-esterification, by determining the removal rate of product fatty acids, may be the major determinant of the stimulation of lipolysis by cAMP.

Animals↗
PubMed1987

Cholesteryl esterase activities in ventricles, isolated heart cells and aorta of the rat.

Cholesteryl esterase activities were determined in homogenates of rat heart (ventricles), isolated, calcium-tolerant, cardiac myocytes and aortic tissue and were compared with acid and neutral triglyceride lipase activities in these fractions. Using cholesteryl oleate/phosphatidylcholine/taurocholate emulsions and digitonin pretreatment of the enzyme fractions, acid and neutral cholesteryl esterase activities were measured in all tissue preparations. In contrast to the acid and neutral triglyceridase and acid cholesteryl esterase activity, the neutral cholesteryl esterase activity was subject to substrate inhibition. Upon isolation of cardiac myocytes, and in contrast with the recovery of neutral triglyceride lipase activity, only a small portion of the neutral cholesteryl esterase (6%) was recovered, suggesting that nonmyocyte neutral cholesteryl esterase activity markedly contributes to the relatively high activity detectable in whole ventricular homogenates. The recovery of large amounts of neutral cholesteryl esterase activity in the supernatant of collagenase-digested heart tissue, obtained during the isolation of myocytes, which is also markedly enriched in activities of two endothelial marker enzymes (5'-nucleotidase and angiotensine-converting enzyme) may indicate the predominant contribution of neutral cholesteryl esterase activity from coronary endothelial cells to this activity detectable in ventricular homogenates. Relative to the activity in ventricular and myocyte homogenates, aorta homogenates possessed the highest specific neutral cholesteryl esterase activity. We propose that in addition to coronary endothelium, smooth muscle cells also contribute to the neutral cholesteryl esterase activity in ventricular homogenates.(ABSTRACT TRUNCATED AT 250 WORDS)

5'-Nucleotidase↗
PubMed1987

A simple and accurate automated system for continuous long-term metabolic studies during artificial ventilation.

Energy expenditure and the amount of metabolised carbohydrate, protein and lipid can be calculated from the O2 consumption, CO2 production and nitrogen excretion using indirect calorimetry. A low-cost automatic system has been developed suitable for short- and long-term measurements during artificial ventilation, in which the gas analysers were calibrated automatically every 10 min and in which the desired variables were calculated and printed every 5 min. O2 and CO2 concentrations of mixed expired and inspiratory gas, the expired minute volume VE, and patient's rectal temperature, were sampled at regular time intervals and a simple programmable calculator with printer was used for the on-line data analysis. Tests on accuracy, stability, reproducibility and feasibility showed this system to be suitable for clinical application.

Autoanalysis↗
PubMed1987

Maximal expiratory and inspiratory flow-volume curves in bilateral vocal-cord paralysis. Changes after surgical treatment and comparison with glottic resistance characteristics.

The maximal expiratory flow-volume (MEFV) and maximal inspiratory flow-volume (MIFV) curve present maximal attainable flows, plotted against the displaced volume at the mouth during a forced expiratory manoeuvre from total lung capacity (TLC) and a subsequent forced inspiratory manoeuvre from residual volume (RV), respectively. Depending on the glottic resistance characteristics, the usual flow limitation may be absent during forced expiration, drastically influencing the form of MEFV curves. During forced inspiration however, the flow remains effort-dependent. We tested this hypothesis by comparing the form of MEFV and MIFV curves, and the glottic resistance characteristics, before and after an endolaryngeal superolateralization of a vocal cord, in 12 patients with bilateral vocal-cord paralysis. Peak expiratory and inspiratory flows were estimated with the aid of the measured glottic resistance characteristics on the assumption that the maximal alveolar pressures were normal during the manoeuvres. The estimated values agreed well with measured values. The form of the MEFV and MIFV curves was also found to be closely linked to the glottic resistance characteristics. It is concluded that the MEFV and MIFV curves are sensitive indicators of flow limitation in patients with upper-airway obstructions.

Adult↗
PubMed1986

Characterization of mono-, di- and triacylglycerol lipase activities in the isolated rat heart.

The lipolytic activities of heart tissue towards full and partial acylglycerols were characterized. Tissue lysosomal, acid lipase activity (pH 4.8) was inhibited by high salt, protamine sulfate, NaF, MgATP, Triton X-100, serum and the esterase-inhibitor diethylparanitrophenyl phosphate. The tissue neutral triacylglycerol lipase activity (pH 7.4) was recovered predominantly in the microsomal and soluble fractions and exhibited essentially identical properties towards activators (serum, apolipoprotein C-II) and reagents (NaCl, Triton X-100, NaF, MgATP and diethylparanitrophenyl phosphate) relative to vascular lipoprotein lipase, except for protamine sulfate which increased the serum-stimulated neutral triacylglycerol lipase activity. Triacylglycerol hydrolysis at acid pH was incomplete, whereas at neutral pH full hydrolysis occurred. Myocardial mono- and diacylglycerol lipase activities, with pH optima of 8.0 and 7.4, respectively, were recovered in the microsomal fraction. They differed immunologically from neutral lipase and lipoprotein lipase and did not bind to heparin-Sepharose 4B. They were kinetically different, partially inhibited by NaCl and differentially affected by protamine sulfate. NaF, Triton X-100 and diethylparanitrophenyl phosphate. Our data suggest that endogenous hydrolytic activity against full and partial acylglycerols is mediated by separate enzymes.

Animals↗
PubMed1986

Studies on the involvement of lipolytic enzymes in endogenous lipolysis of the isolated rat heart.

Rat hearts were depleted in vivo from both the heparin-releasable lipoprotein lipase and heparin-resistant tissue neutral triacylglycerol lipase activity by treatment of the animals with cycloheximide (2 mg/kg body weight), intraperitoneally injected 2.5 and 5 h prior to perfusion. The tissue acid lipase, mono- and diacylglycerol lipase activities were not affected by cycloheximide-induced inhibition of protein synthesis. Myocardial basal and glucagon-stimulated lipolysis, determined by the rate of glycerol production and release from the isolated hearts, was not significantly different in control and cycloheximide-treated rats. Tissue triacylglycerols were recovered with the highest relative specific distribution in the lysosomal fraction isolated from heart homogenates. Upon prolongation of the perfusion-duration the relative specific distribution of triacylglycerols in the lysosomal fraction decreased. In addition, the specific lysosomal triacylglycerol content (micrograms/mg protein) dropped significantly, indicating an important role of lysosomes in myocardial triacylglycerol turnover. Our data strongly suggest that the heparin-resistant neutral triacylglycerol lipase activity may not be the only determinant of endogenous lipolysis in the isolated rat heart and indicate that lipolysis may additionally be mediated by the lysosomal, acid lipase in concert with the microsomal mono-and diacylglycerol lipase.

Adenosine↗