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      Variability of Leptin Values Measured from Different Sample Matrices

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          Abstract

          Leptin concentrations are usually determined in serum or EDTA-treated plasma. Our aim was to evaluate the precision and accuracy of leptin measurement from serum and various kinds of plasma. Blood samples were collected from healthy volunteers and divided into aliquots of serum and plasma with administration of K<sub>2</sub>-EDTA, citrate, fluoride and lithium-heparinate, respectively. Leptin concentrations were measured by a specific radioimmunoassay. There were clear differences between the leptin values from the different matrices. The coefficient of variation (CV) was highest in serum samples (CV: 11.9 %) and very low in K<sub>2</sub>-EDTA-treated plasma samples (CV: 5.3%). Leptin measurements from serum yielded significantly lower results than the respective K<sub>2</sub>-EDTA-treated plasma samples (p < 0.05). The measurement in Li-heparinate-treated plasma revealed similar results to that in K<sub>2</sub>-EDTA-treated plasma. The lowest CV was determined in fluoride-treated plasma (5.2%). A higher CV was determined in citrate-treated plasma (5.8%) and the values were about 25% lower than in the respective K<sub>2</sub>-EDTA-treated plasma samples (p < 0.0001). Lower leptin measurements in citrate-treated plasma may partially, but not in total, be a consequence of dilution by anticoagulating additives. Because of the low CV K<sub>2</sub>-EDTA- and Li-heparinate-treated plasma samples appear most reliable for the measurement of leptin. The usage of these sample matrices is therefore recommended.

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          Most cited references 8

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          Plasma Leptin Levels in Healthy Children and Adolescents: Dependence on Body Mass Index, Body Fat Mass, Gender, Pubertal Stage, and Testosterone

           W F Blum (1997)
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            Dose-dependent cortisol-induced increases in plasma leptin concentration in healthy humans.

             G. Selke,  G Vogler,  S Jack (1998)
            Leptin is a hormone that regulates fat metabolism and appetite. The secretion of leptin is regulated by adiposity and, in the rodent, by factors such as insulin, beta-adrenergic agonists, and glucocorticoids (GCs). Increased secretion of the endogenous human GC, cortisol, occurs during stress and in disorders such as major depression. Pharmacological GCs can robustly increase plasma leptin concentrations in humans, leading us to hypothesize that cortisol may serve as a physiological regulator of human leptin secretion. A randomized double-blind placebo-controlled comparison of 2 fixed oral dosages of cortisol (40 mg/d and 160 mg/d), given for 4 days to matched groups of healthy subjects (n=47). Low-dose treatment approximated GC output during mild stress, while high-dose treatment approximated GC output during maximal stress, spanning a range of GC secretion relevant to physiological stress. Cortisol produced dose-dependent and time-dependent increases in plasma leptin concentrations (time x treatment condition x body mass index; F6,123=10.73; P<.001). Initial treatment-induced increases in plasma leptin concentration returned toward baseline values during 4 treatment days, suggesting tolerance to this GC effect in these healthy subjects. The results indicate an important role for GCs in the short-term regulation of human leptin secretion. Glucocorticoid-induced increases in leptin secretion suggest a mechanism that may contribute to anorexia and weight loss during stress and disease states such as major depression, if these conditions are associated with sustained increases in plasma leptin concentrations.
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              Longitudinal Analysis of Maternal Serum Leptin Levels during Pregnancy, at Birth and Up To Six Weeks after Birth: Relation to Body Mass Index, Skinfolds, Sex Steroids and Umbilical Cord Blood Leptin Levels

              Leptin is an important regulator of body fat mass and energy expenditure during adult life. The mechanisms by which maternal and fetal weight are regulated during pregnancy are poorly understood. In order to gain more insight into a potential role of leptin during gestation, a prospective, longitudinal study was carried out to measure leptin concentrations in maternal serum of 29 healthy women during pregnancy up to 6 weeks after birth and also in umbilical cord blood of their newborns. Leptin concentrations were measured using a specific RIA. In addition, estradiol, testosterone, and sex hormone binding globulin were determined using commercially available RIAs. The mothers’ skinfolds were determined at four sites using a Holtain caliper.Leptin levels increased continuously during pregnancy and reached 25.8 ± 14.7 ng/ml at 38–40 weeks. At birth, leptin concentrations were 23.5 ± 15.4 ng/ml. Three days after delivery a significant decrease of leptin levels to 10.6 ± 6.0 ng/ml was observed. Six weeks after birth the leptin concentration in maternal serum was 13.8 ± 8.6 ng/ml. At birth, maternal serum levels were significantly higher than levels in cord blood and did not correlate with leptin levels in cord blood or neonatal weight. Furthermore, leptin levels did not correlate with maternal sex steroids and sex hormone binding globulin levels. At 6–8 weeks of pregnancy, maternal leptin serum levels correlated significantly with BMI (r = 0.81). The correlation coefficients (leptin vs. BMI) dropped with increasing gestational age and at birth only a poor correlation persisted (r = 0.50). Six weeks after birth there was again a high correlation between leptin levels in maternal serum and BMI (r = 0.76). Subscapular skinfold thickness was correlated to leptin concentrations in maternal serum during the whole period of the investigation.In conclusion, maternal leptin levels continuously increased from 6–8 weeks up to 38–40 weeks of pregnancy. Maternal leptin levels decreased dramatically after birth. Six weeks after delivery, leptin levels were comparable to the values measured at the beginning of pregnancy. We hypothesize that leptin might play an important role during pregnancy and fetal development.
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                Author and article information

                Journal
                HRE
                Horm Res Paediatr
                10.1159/issn.1663-2818
                Hormone Research in Paediatrics
                S. Karger AG
                1663-2818
                1663-2826
                2000
                2000
                15 February 2001
                : 54
                : 1
                : 26-31
                Affiliations
                aKlinik mit Poliklinik für Kinder und Jugendliche, Friedrich-Alexander-Universität Erlangen-Nürnberg, und bLilly Deutschland GmbH, Bad Homburg, Deutschland
                Article
                63433 Horm Res 2000;54:26–31
                10.1159/000063433
                11182632
                © 2001 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 3, References: 24, Pages: 6
                Categories
                Original Paper

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