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Biomedical subjects

A Wennmalm

Publications and source records attributed to A Wennmalm.

At least 19 recordsLinked to original sources
PubMed2001

Evidence that the major oxysterols in human circulation originate from distinct pools of cholesterol: a stable isotope study.

The major oxysterols in human circulation are 7 alpha-, 27-, and (24S)-hydroxycholesterol. Two unique experiments were performed to elucidate their origin and kinetics. A volunteer was exposed to (18)O(2)-enriched air. A rapid incorporation of (18)O in both 7 alpha- and 27-hydroxycholesterol and disappearance of label after exposure were observed. The half-life was estimated to be less than 1 h. Incorporation of (18)O in (24S)-hydroxycholesterol was not significant. In the second experiment a volunteer was infused with liposomes containing 10 g of [(2)H(6)]cholesterol. This resulted in an enrichment of plasma cholesterol with (2)H of up to 13%, and less than 0.5% in cerebrospinal fluid cholesterol. The content of (2)H in circulating 7 alpha-hydroxycholesterol remained approximately equal to that of plasma cholesterol and decreased with a half-life of about 13 days. The (2)H content of circulating 27-hydroxycholesterol was initially lower than that of cholesterol but in the last phase of the experiment it exceeded that of cholesterol. No significant incorporation of (2)H in (24S)-hydroxycholesterol was observed. It is evident that 7 alpha-hydroxycholesterol must originate from a rapidly miscible pool, about 80% of 27-hydroxycholesterol from a more slowly exchangeable pool, and more than 90% of (24S)-hydroxycholesterol from a nonexchangeable pool, presumably the brain. The results are discussed in relation to the role of oxysterols in cholesterol homeostasis and their use as markers for pathological conditions. - Meaney, S., M. Hassan, A. Sakinis, D. Lütjohann, K. von Bergmann, A. Wennmalm, U. Diczfalusy, and I. Björkhem. Evidence that the major oxysterols in human circulation originate from distinct pools of cholesterol: a stable isotope study. J. Lipid Res. 2001. 42: 70;-78.

Blood Circulation↗
PubMed2000

Diurnal variation of flow-mediated vasodilation in healthy premenopausal women.

The present study was designed to test the hypothesis of a diurnal variation of endothelial function. Sixteen healthy, nonsmoking women were studied, each on four occasions during one 24-h period (2:00 PM, 8:00 PM, 2:00 AM, and 8:00 AM). Endothelial function was assessed by ultrasound determinations of flow-mediated vasodilation (FMD%) in the brachial artery. FMD% was contrasted with endothelium-independent vasodilation, i.e., nitroglycerine-induced vasodilation (NTG%). Additionally, plasma concentrations and urinary excretion of nitrate and cGMP were analyzed. FMD% and NTG% displayed diurnal, albeit not parallel, patterns of variation. Whereas FMD% gradually increased from 2:00 PM and peaked at 2:00 AM (means +/- SE: 3.1 +/- 0.4, 4.4 +/- 0.4, 5.1 +/- 0.9, and 3.9 +/- 0.8%), the NTG% demonstrated a nadir at 2:00 AM. Plasma levels and urinary excretion of nitrate and cGMP did not display diurnal variation and no clear association with the variations seen in FMD% and NTG%. This study demonstrates a diurnal variation in both endothelium-dependent and -independent vasodilation in the brachial artery of healthy women. The background and possible implication of such a variation require further studies.

Adult↗
PubMed1999

Detection of an approximately 100 kD protein with strong immunoreactivity to antibodies specific for inducible nitric oxide synthase (iNOS) but without NOS activity in neutrophils of patients suffering from sepsis: results of a preliminary study.

OBJECTIVE: The study was designed to evaluate the expression of inducible nitric oxide synthase (iNOS) in activated human neutrophils. SUBJECTS AND METHODS: By Western blotting and immunocytochemical staining, iNOS expression was analyzed in neutrophils from patients with sepsis who we classified by high plasma nitrate as subjects with activated NO metabolism. For comparison, rats treated with Zymosan documented to induce iNOS were analyzed. RESULTS: Strong immunoreactivity to antibodies for iNOS was detected in leukocytes of Zymosan treated rats and in neutrophils of septic patients. Such immunoreactivity was absent in untreated rats and healthy subjects. In rats, the immunoreactivity was associated to the 130 kD protein as expected for iNOS. In contrast, the intense iNOS staining in neutrophils of septic patients was associated to an approximately 100 kD protein. Despite the iNOS staining, no increased NOS activity could be demonstrated in the neutrophils of septic patients. CONCLUSIONS: The detection of an approximately 100 kD protein with immunoreactivity to antibodies recognizing human iNOS but without NOS activity in neutrophils of patients with sepsis should initiate studies to elucidate the origin and function of this protein.

Animals↗
PubMed1999

An 18oxygen inhalation method for determination of total body formation of nitric oxide in humans.

The formation of nitric oxide (NO) and the subsequent conversion of the NO formed into nitrate require molecular oxygen. Based on this fact, we have recently developed a method using inhalation of the stable oxygen isotope, i.e. 18O2, to determine total formation of NO in small laboratory animals. The method has now been further developed to be applicable also in humans. Five healthy awake male subjects inhaled a gas mixture of unlabelled and 18-labelled oxygen (approximate ratio 4:1) in nitrogen from a closed breathing system equipped with eliminators for carbon dioxide and water vapour. The ratio of unlabelled to 18-labelled oxygen, as well as the total oxygen concentration during the inhalation, were monitored. Venous blood samples were taken before and after the inhalation for analysis of unlabelled and 18O-labelled nitrate by gas chromatography/mass spectrometry. The procedure was repeated with the same protocol on a later occasion, during ongoing treatment with the NO synthesis inhibitor NG-monomethyl-L-arginine (L-NMMA). The average nitrate level in plasma in the absence of L-NMMA was 26 micromol l-1. The rate of total synthesis of NO was estimated to be 0.38 +/- 0.06 mu mol kg-1 h-1, corresponding to a total body formation of 600-700 mu mol/24 h in an adult male. Infusion of L-NMMA caused an increase in mean arterial blood pressure from 86 +/- 4 to 99 +/- 5 mmHg (P<0.05). The average plasma level of nitrate during infusion of L-NMMA was 24 mu mol l-1. NO formation during infusion of L-NMMA was 0.17 +/- 0.03 mu mol kg-1 h-1, i.e. significantly (P<0.05) lower than in the absence of L-NMMA. We suggest that the described method allows direct determination of total NO formation in man. The method may be useful in the study of various experimental and pathophysiological conditions affecting NO formation.

Administration, Inhalation↗
PubMed1998

Estimation of total rate of formation of nitric oxide in the rat.

Nitric oxide (NO) is a powerful mediator with important actions in several organ systems. NO is synthesized during the enzymatic conversion of l-arginine and molecular oxygen to L-citrulline. About 90% of the NO formed is degraded to nitrate. Utilizing this information we have developed a method for assessment of the total rate of formation of NO in the rat. Male Wistar rats were kept in a closed-cage system allowing controlled breathing of a mixture of 18O2 and 16O2 in N2 for up to 5h. Blood samples for mass spectrometric analysis of nitrate residues with varying numbers of 18O atoms incorporated were drawn before and during the exposure to 18O2. By comparing the relative incorporation of 18O into nitrate residues to the 16O2/18O2 ratio in the breathing gas mixture in the cage system it was possible to calculate the absolute rate of NO formation in the animal. The rate of formation of NO in anaesthetized rats ranged from 0.33 to 0.85 micromol.kg-1.h-1. The rate of formation did not differ significantly in rats which were awake during the experiment (range 0.36-0.72 micromol.kg-1.h-1). The L-arginine analogue Nomega-nitro-L-arginine methyl ester (L-NAME) dose-dependently inhibited the formation of NO, at a dose of 100mg/kg by more than 99%. The technique presented allows estimation of the total rate of formation of NO in vivo in rats. Application of the technique may yield important information about the physiological and pathophysiological roles of NO. It may also be utilized to evaluate the effect of pharmacological treatment on NO formation.

Animals↗
PubMed1998

Effect of nitric oxide gas on platelets during open heart operations.

BACKGROUND: The increased bleeding tendency observed after cardiopulmonary bypass is caused in part by thrombocytopenia and impaired platelet function induced by the procedure. Previous in vitro studies have shown that nitric oxide (NO) added to the oxygenator sweep gas reduces platelet activation during experimental perfusion. We evaluated the effect of 40 ppm of NO, added to the oxygenator sweep gas, on platelet consumption and activation in patients undergoing cardiopulmonary bypass. METHODS: Twenty patients scheduled to undergo cardiopulmonary bypass were randomized to either the control or the NO arm of the study. Their platelet count, plasma beta-thromboglobulin level, platelet membrane glycoprotein Ib and IIb/IIIa levels, adenosine diphosphate-induced platelet aggregation, plasma nitrate level, and plasma hemoglobin were assayed before, during, and after cardiopulmonary bypass. RESULTS: After operation, slightly higher platelet counts were observed in the NO-treated patients than in the control patients, which might indicate a lower degree of platelet adhesion to the artificial surfaces of the extracorporeal circuit. However, this difference did not reach statistical significance. In addition, a difference in platelet membrane expression of glycoprotein Ib was seen between the NO and control groups after operation; the platelets of the control patients had significantly higher glycoprotein Ib expression than those of the NO-treated patients. The results of platelet aggregometry indicated preserved platelet function in both the NO-treated and control patients. The blood methemoglobin levels also were low in both groups. CONCLUSIONS: Nitric oxide might reduce the platelet consumption encountered during cardiopulmonary bypass without having any adverse effect on platelet function, as reflected by the preserved aggregation response seen in our patients. However, the best route of NO administration and the optimum dose remain to be established.

Adenosine Diphosphate↗
PubMed1998

Urinary albumin excretion and heart rate variability in obese women.

OBJECTIVE: The aim of this work was to examine the relationship between cardiac autonomic function and urinary albumin excretion in obesity. SUBJECTS: These were 27 obese non-diabetic postmenopausal women and 18 non-obese healthy postmenopausal women. MEASUREMENTS: Urinary albumin excretion as well as plasma nitrate, both indices of capillary function, were measured. Power spectral analysis of heart rate variability was performed, as a measurement of vagal function. An oral glucose tolerance test (OGTT) was performed and blood lipids were analysed. RESULTS: The obese women were characterized by higher fasting insulin, sum of glucose, triglycerides and lower high density lipoprotein cholesterol (HDL), the latter of borderline significance, than controls. Urinary albumin excretion (UAE), plasma nitrate and heart rate variability were not different between obese and control women. However, in obese women log UAE correlated positively with systolic and diastolic blood pressure, and inversely with heart rate variability, the latter independent of body mass index (BMI) and the waist/hip circumference ratio. CONCLUSION: It was concluded that this inverse association between UAE and parasympathetic activity in obese women may be an early sign of derangements of endothelial function and autonomic nervous system control, which may contribute to the increased risk of cardiovascular mortality in abdominal obesity.

Aged↗
PubMed1998

Increase in nitric oxide formation after chronic voluntary exercise in spontaneously hypertensive rats.

The effect of chronic voluntary exercise on the plasma level of nitrate, a major stable metabolite of nitric oxide (NO) was studied in spontaneously hypertensive rats (SHR). Exercise consisted of spontaneous running in wheels for 3-35 days. Blood samples were collected after 3, 7, 14, 21 and 35 days of exercise and all samples were drawn after the running wheel had been locked during the preceding 12 h. The plasma nitrate level was significantly (P < 0.05) elevated in SHR after 35 days of exercise. Surprisingly after 7 days of exercise a significant (P < 0.001) decrease in the nitrate level in plasma was noted. Further research is needed to elucidate this biphasic change in nitrate seen in this study. The elevated level of plasma nitrate seen after 35 days of voluntary exercise was still present up to 36 h after termination of exercise. We conclude that exercise training in SHR elicits an enhanced formation of NO.

Animals↗
PubMed1997

Importance of a novel oxidative mechanism for elimination of brain cholesterol. Turnover of cholesterol and 24(S)-hydroxycholesterol in rat brain as measured with 18O2 techniques in vivo and in vitro.

The brain is the most cholesterol-rich organ in the body. Brain cholesterol is characterized by a very low turnover with very little exchange with lipoproteins in the circulation. Very recently we showed that there is a continuous age-dependent flux of 24(S)-hydroxycholesterol from the human brain into the circulation (Lütjohann, D., Breuer, O., Ahlborg, G., Nennesmo, I., Sidén, A., Diczfalusy, U., and Björkhem, I. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 9799-9804). Here we measured the rate of synthesis of cholesterol as well as the conversion of cholesterol into 24(S)-hydroxycholesterol in rat brain in vivo with use of an 18O2 inhalation technique and mass isotopomer distribution analysis. Cholesterol synthesis was found to correspond to 0.03 +/- 0.01% of the pool per h. Conversion of cholesterol into 24(S)-hydroxycholesterol was of a similar magnitude, about 0.02% of the pool per h. Brain microsomes converted endogenous cholesterol into 24(S)-hydroxycholesterol at a similar rate when incubated in the presence of NADPH. When incubated with whole homogenate and subcellular fractions of rat brain, there was no significant conversion of tritium-labeled 24-hydroxycholesterol into more polar products. Plasma from 18O2-exposed rats contained 24(S)-hydroxycholesterol with an enrichment of 18O similar to that in 24(S)-hydroxycholesterol in the brain. The results suggest that the present 24(S)-hydroxylase mediated mechanism is most important for elimination of cholesterol from the brain of rats. There is a slow conversion of brain cholesterol into 24(S)-hydroxycholesterol with a rapid turnover of the small pool of the latter oxysterol due to leakage to the circulation (half-life of brain 24(S)-hydroxycholesterol is about 0.5 days as compared with 2-4 months for brain cholesterol). It is evident that the 24(S)-hydroxylation greatly facilitates transfer of cholesterol over the blood-brain barrier and that this hydroxylation may be critical for cholesterol homeostasis in the brain.

Animals↗
PubMed1997

Transformation of subcutaneous nitric oxide into nitrate in the rat.

Following its addition to arterialized blood in vitro, nitric oxide (NO) is transformed into nitrate in the erythrocytes. Inhaled NO is similarly transformed into nitrate in the blood in vivo. These observations suggest that nitrate is a universal end-metabolite of NO, i.e. of endogenously formed NO as well. However, endogenous NO may also be inactivated in tissues, i.e. outside the vascular lumen. To study the fate of NO metabolized with delayed access to the blood, rats were given subcutaneous injections of 15NO or K15NO3, and the plasma concentrations of 15NO3(-) were followed for 450 min after injection. The values for the distribution volume and plasma decay (t12) of 15NO3(-) did not differ between rats given 15N-labelled NO and NO3(-). The area under the plasma decay curve for rats given 15NO amounted to 89% of the corresponding area for animals given K15NO3. This demonstrates that 15NO, when given extravascularly in millimolar concentrations, is mainly transformed into 15N-labelled nitrate. Other rats were kept in an atmosphere containing a mixture of 16O2 and 18O2. Nitrate residues containing either one or two 18O atoms were isolated from the blood, indicating that inhaled oxygen was incorporated during both the formation of NO and the subsequent transformation of NO into nitrate. The fraction of nitrate residues containing two 18O atoms was larger than that containing one 18O atom. We propose that nitrate is a major stable metabolite of endogenous NO that does not primarily diffuse into the vascular lumen following formation. Hence nitrate seems to be the quantitatively most important end-product of the metabolism of endogenous NO. The transformation of endogenous NO into nitrate involves the incorporation of inhaled oxygen.

Animals↗
PubMed1997

Seasonal variations in cyclic GMP response on whole-body cooling in women with primary Raynaud's phenomenon.

1. Primary Raynaud's phenomenon (PRP) is characterized by increased vasoconstrictor tone that develops during exposure to cold. The symptoms are most pronounced during the winter months with low outdoor temperature. The L-arginine-nitric oxide (NO)-cyclic GMP (cGMP) pathway plays an important role in counteracting vasospasm. The aim of the present study was to investigate if the venous cGMP response to whole-body cooling in women with PRP varied with the season of the year. 2. The study was performed as an open parallel-group comparison between women with PRP and healthy female controls during the winter months of February 1994 and 1995 and in the summer month of August 1994. Blood samples were drawn just before and 40 min after whole-body cooling. 3. There were no significant changes in venous cGMP after whole-body cooling in women with PRP during the winter months of February 1994 and 1995. Cold exposure in the summer month of August resulted, however, in a significant increase in venous cGMP (P < 0.01). In contrast, the healthy women responded with a significant increase in venous cGMP on all three test occasions: February 1994 (P < 0.05), August 1994 (P < 0.05) and February 1995 (P < 0.01), 4. A seasonal variation in venous cGMP response to whole-body cooling was observed only in women with PRP. Healthy women responded to cold exposure with an increase in venous cGMP during summer and winter, whereas females with PRP showed an increase only during summer. Results from the present study might indicate seasonal variation in the regulation of constitutive nitric oxide synthetase in women with PRP, which may contribute to new therapeutic approaches.

Adult↗
PubMed1997

Plasma nitric oxide metabolite in women with primary Raynaud's phenomenon and in healthy subjects.

Primary Raynaud's phenomenon (PRP) is characterized by cold- or stress-induced transient attacks of impaired skin circulation in fingers and/or toes. PRP displays seasonal variation with less severe symptoms in the summer. The aetiology has not been clarified. The aims of the present study were (a) to assess the influence of cold exposure on the plasma levels of the nitric oxide (NO) metabolite, nitrate, in patients with PRP and in healthy control subjects; and (b) to investigate whether there is a seasonal variation in these plasma levels. In a group of women with PRP and matched control subjects, venous blood was sampled before and at the end of a 40-min period of whole-body cooling. The study was performed with the same protocol on two occasions; once in the winter and once in the summer. A seasonal variation was detected with higher plasma levels of nitrate in the winter than in the summer, both in PRP and in control subjects. However, the plasma level of nitrate was not changed in response to cold exposure on any occasion, either in the patient or in the control group. Our study indicates that NO formation is up-regulated in response to cold weather in both study groups. However, NO formation does not seem to be increased in response to whole-body cooling, either in PRP patients or in healthy subjects. Further investigations are required to reveal whether the observed seasonal variation in NO formation is a universal phenomenon in man.

Adult↗
PubMed1997

Both physical fitness and acute exercise regulate nitric oxide formation in healthy humans.

We analyzed nitrate, a major stable end product of nitric oxide (NO) metabolism in vivo in plasma and urine from groups of healthy subjects with different working capacities. Resting plasma nitrate was higher in athletic subjects than in nonathletic controls [45 +/- 2 vs. 34 +/- 2 (SE) microM; P < 0.01]. In other subjects, both the resting plasma nitrate level (r = 0.53; P < 0.01) and the urinary excretion of nitrate at rest (r = 0.46; P < 0.01) correlated to the subjects' peak work rates, as determined by bicycle ergometry. Two hours of physical exercise elevated plasma nitrate by 18 +/- 4 (P < 0.01) and 16 +/- 6% (P < 0.01), respectively, in athletes and nonathletes, compared with resting nitrate before exercise. We conclude that physical fitness and formation of NO at rest are positively linked to each other. Furthermore, a single session of exercise elicits an acute elevation of NO formation. The observed positive relation between physical exercise and NO formation may help to explain the beneficial effects of physical exercise on cardiovascular health.

Adult↗
PubMed1997

The arginine-nitric oxide pathway in thrombotic microangiopathy.

Eleven patients with thrombotic thrombocytopenic purpura (TTP) or haemolytic uremic syndrome (HUS) were investigated with respect to plasma concentrations of L-arginine, a substrate for nitric oxide (NO) and asymmetrical dimethyl arginine (ADMA), during active disease and after recovery. Plasma concentration of NO3-, the degradation product of NO, was also analyzed. The patients were treated with fresh-frozen plasma and plasmapheresis. One of the patients had experienced relapses of TTP five times during the preceding year. After treatment with p.o. arginine hydrochloride 1.5 g x 3 was started, no relapse has occurred during a 12-month period. During the active phase the plasma concentration of arginine was low and that of NO3- was very high, indicating a high NO-synthesis rate. The arginine concentration normalized on recovery. Plasma levels of ADMA, was twice normal during active disease, and did not return to normal on recovery. In conclusion, patients with TTP/HUS exhibit signs of activation of the NO-synthesis.

Adult↗
PubMed1996

Dietary cholesterol induces transient changes in plasma nitrate levels in rabbits that are correlated to microcirculatory changes.

Dietary treatment of rabbits with 1% cholesterol resulted in a transient rise in their plasma nitrate levels. After 3 weeks of treatment the nitrate levels were about 50% higher than those of the controls (p<0.005). After 10 weeks of treatment the nitrate levels were similar to those at the start of the study. In accordance with previous work (Xiu et al., J. Clin. Invest., 1994, 93, 2732-2737), the cholesterol treatment let to a decreased blood flow velocity in arterioli of the third order in the conjunctiva, and a decreased diameter of these arterioli. There was a significant correlation between plasma nitrate levels and the two microcirculatory variables (p<0.0001). Nitrate is the major metabolic end product of nitric oxide (NO), and plasma nitrate levels may be used as an index of the endogenous formation of NO. The present results suggest that dietary cholesterol induces a transient increase in the synthesis of NO. Such an increased synthesis may compensate for part of a cholesterol-induced degradation of NO.

Animals↗
PubMed1996

Apoptotic death of human leukemic cells induced by vascular cells expressing nitric oxide synthase in response to gamma-interferon and tumor necrosis factor-alpha.

The host defense against tumor cells is in part based on the production of nitric oxide (NO) by activated macrophages. However, cells of the blood vessels can also participate in antitumor defense responses. They produce NO either constitutively [endothelial cells (ECs)] or after stimulation by proinflammatory cytokines (ECs and vascular smooth muscle cells). We have used a tumor cell-vascular cell coculture system to evaluate whether vascular cells can mediate cytotoxic effects on tumor cells. Treatment with IFN-gamma and tumor necrosis factor-alpha induced death of human erythroleukemic K562 cells cocultured with rodent vascular smooth muscle cells or ECs. The synergistic antitumor activity of the two cytokines depended on de novo gene expression of the inducible isoform of NO synthase and on synthesis of reactive nitrogen intermediates (RNIs) in the vascular cells. K562 cells did not produce any appreciable levels of NO, but they were targeted by RNIs released from the cytokine-stimulated vascular cells, as demonstrated by electron paramagnetic resonance spectrometry, which showed formation of nonheme iron-nitrosyl complexes in the tumor cells. Assays for mitochondrial respiration demonstrated that the tumor cells suffered from a block of the complexes I and II of the mitochondrial respiratory chain. Further analysis of the cytotoxic mechanism by fluorescent microscopy, flow cytometry, and DNA electrophoresis revealed that K562 cells attacked by NO-producing vascular cells underwent apoptosis with plasma membrane blebbing, cell volume reduction, condensation of cytoplasm and chromatin, and fragmentation of genomic DNA at internucleosomal sites. In contrast, only a few vascular cells exhibited these apoptotic changes, suggesting that these cells resist the RNI attack. Inhibition of NO production in vascular cells by NG-monomethyl-L-arginine, an inhibitor of NO synthases, significantly reduced the death of the K562 cells. These observations suggest that vascular cells induce apoptotic death of tumor cells by producing RNIs in response to cytokine stimulation.

Animals↗
PubMed1996

Nitric oxide in the oxygenator sweep gas reduces platelet activation during experimental perfusion.

BACKGROUND: Hemorrhage is a major complication experienced in 10% to 35% of neonates treated with extracorporeal life support (ECLS). The increased bleeding tendency is partly due to an ECLS-induced thrombocytopenia and impaired platelet function. In the present study, we evaluated the effect of nitric oxide on the ECLS-induced platelet consumption and activation. METHODS: Two identical in vitro ECLS circuits were primed with fresh, heparin-treated human blood and circulated for 24 hours. Nitric oxide (15, 40, or 77 ppm) was added to one of the oxygenators in each pair. Eight paired experiments were performed. Platelet count, plasma beta-thromboglobulin, platelet serotonin content, plasma nitrate, plasma cyclic guanosine monophosphate, and platelet membrane glycoprotein Ib were assayed before the start and at 0.5, 1, 3, 12, and 24 hours of perfusion. RESULTS: Plasma nitrate and plasma cyclic guanosine monophosphate levels were significantly higher in the nitric oxide circuits than in the control circuits (p < 0.01). Higher platelet counts (p < 0.01) and lower beta-thromboglobulin levels (p < 0.01) were observed in the nitric oxide circuits compared with the control circuits. However, no significant differences in platelet serotonin content or platelet membrane glycoprotein Ib density were noted between the circuits. CONCLUSIONS: Nitric oxide probably reduces platelet consumption and platelet activation during ECLS.

Analysis of Variance↗