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Biomedical subjects

O Beck

Publications and source records attributed to O Beck.

At least 37 records · Page 2Linked to original sources
PubMed1998

On the accurate measurement of serotonin in whole blood.

Levels of serotonin (5-hydroxytryptamine; 5-HT) in whole blood reflect the levels in the platelets, but there are problems with instability of 5-HT in measurement of whole blood extracts. We therefore developed and validated an assay for whole blood 5-HT using HPLC with fluorometric detection. The procedure involved collecting blood in EDTA vacutainer tubes and aliquoting it with internal standard, alpha-methyl-5-HT, before freezing. The aliquots were thawed on ice and proteins precipitated with perchloric acid containing EDTA and ascorbic acid. The 5-HT was stable in fresh whole blood for 24 h after sampling when stored at room temperature, refrigerated, or ice-cooled. Measurements of the levels of 5-HT in blood collected in heparin, citrate or EDTA were similar, but in blood collected in ACD-buffer the levels were approximately 25% lower. Cell lysis by sonication decreased the 5-HT levels, but this was compensated for by the internal standard. Determinations of 5-HT by HPLC were in good agreement with those by gas chromatography - mass spectrometry. The intra-individual variability between days was 3.6% (n=6). However, single and repeated ingestion of bananas, which are rich in 5-HT, elevated 5-HT in whole blood, indicating dietary influences on platelet 5-HT.

Adult↗
PubMed1997

Acute interaction between ethanol and serotonin metabolism in the rat.

The effect of acute ethanol on peripheral serotonin (5HT) metabolism was studied in Sprague-Dawley rats. Four hours after a single dose of ethanol (1.0 g/kg) administered into the stomach, a significant increase in the 5HT level in stomach tissue and a decrease in ileum was observed. The level of 5-hydroxyindole-3-acetic acid (5HIAA) was increased in urine, while increased concentrations of 5-hydroxytryptophol (5HTOL) occurred in jejunum, ileum, spleen and urine. After 7-9 h when the blood ethanol concentration had returned to zero, 5HTOL levels were still higher than control values in jejunum, ileum and urine. At 4 h, an elevated ratio of 5HTOL to 5HIAA was observed in urine and ileum (by approximately 2-fold), liver (approximately 3-fold), and spleen (approximately 5-fold), whereas the ratio was reduced in stomach. In urine and spleen, this metabolic shift persisted after 7-9 h. The 5HTOL level in bile was increased by approximately 3.5-fold after 8 h. 5HIAA was not detectable in bile. The present results indicate that the rat has a much higher proportion of 5HTOL formation than man under normal conditions. The rat does not appear to be an ideal model for studying the interaction between ethanol and 5HT metabolism in man.

Animals↗
PubMed1997

Superoxide dismutase reduces islet microvascular injury induced by streptozotocin in the rat.

Intravenous administration of streptozotocin (STZ) leads to permanent diabetes mellitus in rats. We investigated the possible role of islet microcirculatory changes and free radical formation in this animal model. In vivo fluorescence microscopy was performed for 4 h after administration of STZ. Vascular permeability, capillary blood flow, and endothelial leukocyte adhesion were measured in endocrine and exocrine pancreatic tissue. The earliest microcirculatory event was an increase in vascular permeability in pancreatic islets, with a peak 1 h after STZ administration. The difference between islet and exocrine tissue light intensity was +15.8 +/- 5.6% at t = 60 min. Islet blood flow velocity significantly decreased after 3 h, whereas blood flow in the exocrine pancreas was not affected. Complete stasis of islet blood flow was observed only in rats receiving STZ. Neither increased leukocyte adhesion to islet vascular endothelium nor ischemia-reperfusion phenomena were observed. Prophylactic administration of the radical scavenger superoxide dismutase prevented STZ-induced damage to the islet microcirculation in the initial phase of this model. We conclude that STZ leads to severe microcirculatory disturbances within pancreatic islets in rats. Apparently, these changes are mediated at least in part by free oxygen radicals.

Animals↗
PubMed1996

Methotrexate plasma pharmacokinetics: importance of assay method.

Intravenous methotrexate (MTX) therapy is widely used for treatment of various neoplastic diseases in children. The optimization of the MTX dose and/or the subsequent leucovorin rescue is based on pharmacokinetic data calculated from plasma concentrations collected after cessation of the MTX administration. The influence of the MTX assay method on the subsequent pharmacokinetic evaluation was studied in 13 children with acute lymphoblastic leukemia. Plasma samples were collected after administration of MTX (5-8 g/m2) as 24 h infusions. All samples were analyzed by five different analytical procedures, viz. liquid chromatography (LC), enzyme inhibition assay (EIA), two fluorescence polarization immunoassays (FPIA1 and FPIA2) and enzyme multiplied immunoassay (EMIT). Using measurements from the four non-chromatographic procedures, only about 50% of determined pharmacokinetic parameters (area under the plasma concentration time curve, calculated by the trapezoidal rule and from pharmacokinetic modelling, and the terminal half life time) were within the range 75-125% of the values obtained from LC data. We conclude that the clinical outcome of MTX therapy using estimated MTX pharmacokinetics as guidelines for proper dosing of MTX and/or leucovorin rescue might be affected by the lack of accuracy of non-chromatographic procedures for MTX analysis. There is still a need for improving the accuracy of the procedures aimed at therapeutic drug monitoring of MTX.

Adolescent↗
PubMed1996

Local administration of morphine decreases the extracellular level of GABA in the periaqueductal gray matter of freely moving rats.

Opioids are generally believed to activate descending pain inhibitory pathways from the periaqueductal gray matter (PAG). Since opioids exert an inhibitory effect on neural excitability and transmitter release, an opioid-mediated inhibition of tonically active inhibitory gamma-aminobutyric acid (GABA) neurons has been suggested to mediate this effect. The aim of the present microdialysis study was to investigate the effect of local administration of morphine on the extracellular GABA level in the PAG of awake rats. The recently developed and highly sensitive method of capillary electrophoresis with laser-induced fluorescence detection was used for GABA determination in microdialysate samples obtained from the PAG of freely moving rats. The basal GABA level was 54.5 +/- 6.6 nM (n = 8; mean +/- SEM). Perfusion of the dialysis probe with morphine (100 microM) for 30 min significantly decreased the GABA level to 28.2 +/- 4.2 nM (n = 8; P < 0.05). The effect of morphine was reversed by coperfusion with naloxone (100 microM in the perfusion fluid). The present results thus provide direct experimental evidence for an opioid-induced inhibition of tonic GABA release in the PAG, which may in turn lead to a disinhibition of descending pain inhibitory pathways.

Animals↗
PubMed1996

Rectal administration of morphine in children. Pharmacokinetic evaluation after a single-dose.

BACKGROUND: There is limited knowledge about the pharmacokinetics of morphine and its metabolites after rectal administration in children. In this study the pharmacokinetics of two different rectal formulations of morphine were examined and compared with intravenous morphine. METHODS: Children undergoing elective surgery received rectal morphine 0.2 mg/kg before start of surgery. Ten children (mean age 14 months) received morphine rectally in a hydrogel formulation and another 10 children (mean age 16 months) received morphine rectally in a parenteral formulation. For comparison, 6 children (mean age 21 months) were given the same dose intravenously. The plasma concentrations of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) were measured by HPLC over 6 h after drug administration. RESULTS: The mean rectal bioavailability of morphine was 35% (range 18-59) after hydrogel administration and 27% (range 6-93) after the solution. Mean values of Cmax were 76 nmol/l (25-129) and 56 nmol/1 (15-140), respectively. The results showed that morphine gel had a significantly higher bioavailability (P < 0.02) than the solution. The ratios of plasma (M3G + M6G) to morphine were higher after rectal administration (mean 7.5-8.7) than after i.v. injection (mean 5.3), indicating the presence of first-pass metabolism using the rectal route. CONCLUSIONS: The rectal morphine hydrogel has pharmacokinetic properties which makes it a useful formulation for premedication and pain alleviation in paediatric patients.

Administration, Rectal↗
PubMed1996

Evaluation of clinical assays for measuring high-dose methotrexate in plasma.

Four routine assays commonly used for monitoring plasma methotrexate (MTX) during high-dose therapy were validated by HPLC as the comparison method. MTX and its main metabolite, 7-hydroxymethotrexate (7-OHMTX), were analyzed by HPLC with postcolumn derivatization and fluorometric detection. About 200 clinical plasma samples from 13 children with acute lymphoblastic leukemia who received 5-8 g/m2 MTX as 24-h infusions were analyzed. The fraction of measured concentrations of MTX that were within 75-125% of the values obtained by HPLC were 64.5% for enzyme inhibition assay, 56.4% for fluorescence polarization immunoassay with polyclonal antibodies (FPIA1; Abbott), 58.9% for FPIA2 (with monoclonal antibodies; Abbott), and 46.4% for enzyme-multiplied immunoassay (Emit; Syva). All nonchromatographic procedures were subject to interferences from MTX plasma metabolites or endogenous substances. The interference from 7-OHMTX was, however, somewhat less pronounced for FPIA2 (monoclonal) than for FPIA1 (polyclonal).

Child↗
PubMed1996

Laboratory testing for recent alcohol consumption: comparison of ethanol, methanol, and 5-hydroxytryptophol.

The ratio of 5-hydroxytryptophol to 5-hydroxyindole-3-acetic acid (5HTOL/5HIAA) in urine was compared with concentrations of ethanol and methanol as a way to monitor recent alcohol consumption. During detoxification of alcohol-dependent subjects, ethanol persisted longer in urine than in breath or plasma. Blood and urinary methanol remained increased for 2-6 h after blood ethanol had returned to background concentrations, whereas 5HTOL/5HIAA remained increased for 6-15 h. In healthy volunteers who had ingested alcohol (range 3-98 g) the previous afternoon or evening, 87% (for men) and 59% (for women) of all drinking occasions exceeding 7 g of alcohol were identified by an increased 5HTOL/5HIAA in the first morning urine void. This compared with 32% and 12%, respectively, identified by analysis of ethanol (>200 micromol/L). No gender difference in the excretion pattern of 5HTOL/5HIAA was seen. The results demonstrate that 5HTOL/5HIAA provides a specific and more sensitive method to detect recent alcohol consumption than does ethanol or methanol.

Adult↗
PubMed1995

Simultaneous quantitation of methotrexate and its two main metabolites in biological fluids by a novel solid-phase extraction procedure using high-performance liquid chromatography.

We have developed an assay for the simultaneous determination of methotrexate (MTX) and its main metabolites, 7-hydroxymethotrexate (7-OHMTX) and 2,4-diamino-N10-methylpteroic acid (DAMPA) in plasma, urine and saliva meeting the requirement of rapidity for routine use in high-dose MTX therapy and the requirement of sensitivity for its potential use in therapeutic drug monitoring in low-dose MTX therapy. Sample preparation is based on solid-phase extraction using C8 Isolute cartridges. Chromatographic separation was achieved with a reversed-phase column (C18), and quantitation by subsequent exposure to UV light of 254 nm, which converted MTX and its two metabolites by photolytic oxidation to fluorescent products. The recoveries of MTX, 7-OHMTX and DAMPA from plasma at 100 nmol/l were 85.8, 91.1 and 102.3%, respectively. The limits of detection for MTX, 7-OHMTX and DAMPA in plasma and saliva were 0.1 nmol/l. In urine the limit of detection was 10 nmol/l for all compounds. The limits of quantitation in plasma and saliva were 0.5 nmol/l for all compounds.

Chromatography, High Pressure Liquid↗
PubMed1995

Methotrexate in juvenile rheumatoid arthritis. Evidence of age dependent pharmacokinetics.

Children with juvenile rheumatoid arthritis (JRA) have been reported to require higher doses (per kg body weight) of methotrexate (MTX) than adults with rheumatoid arthritis to control their disease. The purpose of the present study was to characterise the plasma pharmacokinetics of MTX and its major metabolite, 7-hydroxymethotrexate (7-OHMTX) in children, and to compare the results with those previously obtained in adults. Thirteen patients (age 5-16 y) with JRA (median disease duration 5.5 y) were studied after once weekly oral administration of MTX (median 0.21 mg.kg-1). The analytical method was sufficiently sensitive to permit determination of plasma and urinary concentrations of MTX and 7-OHMTX during the entire dose interval in most of the patients. The dose normalized area under the plasma concentration versus time-curve (AUC) of MTX increased with the age of the children and was lower than previously found in adults. The dose normalized AUC of 7-OHMTX was not dependent on age. No correlation was found between the AUCs of MTX and 7-OHMTX. The results suggest that the age-dependence of the pharmacokinetics of MTX might explain the observation that at least some children require higher doses of MTX than adults to obtain a sufficient therapeutic effect.

Adolescent↗
PubMed1995

Subjective and objective symptoms in relation to plasma methadone concentration in methadone patients.

Two rating scales, which were originally developed for measurements of objective and subjective signs of opiate withdrawal, were used to evaluate potential estimates (correlates) of methadone effects in relation to plasma methadone concentrations. Patients participating in our regular methadone maintenance treatment project were studied during 24 h after the intake of the daily methadone dose. Methadone concentrations in plasma were compared to the subjective (estimated by the patients) and objective (estimated by the investigator) signs of the drug effects before, and 2.5, 5, 9 and 24 h after intake of methadone. Some new items possibly related to rising methadone concentrations were added to the subjective scale. Results indicated that, for subjective ratings, the majority of the items investigated corresponded well with the plasma methadone concentrations. The most significant associations were found for the following items: low psychomotor speed, alertness, running nose, yawning and anxiety. For objective ratings, only the items rhinorrhea, piloerection and signs of anxiety were significantly associated with the methadone concentrations. These rating scales may, together with plasma methadone determinations, be of considerable value when making dose adjustments for methadone maintenance patients. Further work is, however, needed to establish concentration-effect relationships.

Adult↗
PubMed1995

5-Hydroxytryptophol conjugation in man: influence of alcohol consumption and altered serotonin turnover.

The distribution of free and conjugated forms of the serotonin (5-hydroxytryptamine) metabolite 5-hydroxytryptophol (5HTOL) in human urine was determined. 5HTOL was analyzed using a sensitive and specific gas chromatographic-mass spectrometric method. The sulfate and glucuronide conjugated forms were measured indirectly following enzymatic hydrolysis. Total 5HTOL levels in control samples ranged between 98-301 nM, in samples collected following ingestion of bananas, a food rich in serotonin, between 450-3292 nM, following alcohol consumption between 863-13326 nM, and in samples obtained from patients with serotonin producing carcinoid tumors between 1695-3793 nM. Free 5HTOL accounted for less than 4% of total 5HTOL in all samples. Sulfate conjugated 5HTOL was calculated to comprise about 17% of total 5HTOL in the control samples and 15% in the alcohol samples, whereas the mean proportion was significantly increased to 33% and 27% in the samples collected after ingestion of bananas and from patients with carcinoid tumors, respectively. The results show that conjugation with glucuronic acid followed by urinary excretion is normally the predominant route for elimination of 5HTOL in man. However, in situations of elevated levels of total 5-hydroxyindoles originating from dietary sources or serotonin producing tumors in the gut, sulfate conjugation becomes more important.

Adult↗
PubMed1995

Determination of 5-hydroxytryptophol in urine by high-performance liquid chromatography: application of a new post-column derivatization method with fluorometric detection.

The aim of the present study was to develop a high-performance liquid chromatographic (HPLC) method for determination of the serotonin metabolite 5-hydroxytryptophol (5HTOL) in human urine. 5HTOL was liberated from its conjugated form by enzymatic hydrolysis and isolated by a sample clean-up procedure on a small Sephadex G-10 column. The eluate was injected onto an isocratically eluted C18 reversed-phase column and 5HTOL was converted into a fluorescent oxazole derivative by on-line post-column reaction with benzylamine in the presence of potassium hexacyanoferrate(III). The limit of detection was about 10 nM and the intra-assay coefficients of variation were below 4% with urine samples and standard solutions. The results indicate that the method can be used as a screening method to discriminate between normal and elevated levels of total (free + conjugated) 5HTOL in urine.

Chromatography, High Pressure Liquid↗
PubMed1995

Flunarizine of limited value in children with intractable epilepsy.

Fourteen ambulatory children and adolescents with intractable epilepsy were studied in an open phase II study to investigate the pharmacokinetics and pharmacodynamics of flunarizine as an add-on treatment. Flunarizine was given in increasing doses starting with 0.1-0.3 mg/kg/day until effect was observed or a steady-state plasma concentration of 50-60 ng/ml was reached. Treatment was continued for 3 months at steady state. Pharmacokinetics were determined during the immediate posttreatment period. Positive antiepileptic effect (> or = 50% reduction in seizure frequency) was observed in 4 of 14 patients (29%; 95% CI: 52-5). Independently of antiepileptic effect, 10 of 14 parents (71.4%; 95% CI: 95-48) observed positive cognitive effects. In all patients treatment was withdrawn due to either lack of effect or weight gain. Flunarizine was rapidly absorbed; mean time of peak concentration (Tmax) was 2.7 hours (range: 1-8). The mean terminal half-life was 23.2 days (range: 7-48), the total plasma clearance of flunarizine per fraction of the dose absorbed (CLp/F) was 0.28 ml/min/kg (range: 0.07-042), and the volume of distribution of flunarizine per fraction of the dose absorbed (Vd/F) was 187 L/kg (range: 99-348). We conclude that flunarizine (0.1-0.3 mg/kg/day) seems to be of limited antiepileptic value in children with intractable epilepsy. The pharmacokinetic profile of flunarizine complicates its clinical use.

Adolescent↗