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BACKGROUND: The bladder exstrophy-epispadias complex represents a spectrum of urogenital anomalies in which part or all of the distal urinary tract fail to close and are exposed on the outer abdominal wall. Previous studies are suggestive of an underlying multifactorial mode of inheritance. However, no genetic or nongenetic factor has been identified so far. In this study, we sought risk loci by parametric and nonparametric linkage analysis, searching for homozygous segments, and more complex inherited loci, respectively. METHODS: Two pedigrees, Spanish and German, each comprising two members affected with classical bladder exstrophy, were analyzed by genome-wide linkage scan. RESULTS: Evidence for possible risk/modifying loci on chromosomes 2p22.1-p21, 2p25.2-p25.1, 4q23-q32.3, 7q21.3-q33, 7q34-q36.1, 14q31.1-q32.2, and 19q13.33-q13.43 (LOD scores >1.50) was obtained. CONCLUSIONS: This study was the first positional approach to identify chromosomal candidate regions causally related to bladder exstrophy-epispadias complex. Our results suggest the presence of susceptibility genes in the regions identified. These regions need to be confirmed in future studies.

Background: The StatSensor® Xpress-i™, a point-of-care system for blood creatinine measurement, offers patients the possibility of self-monitoring creatinine. In this study, the analytical performance of the StatSensor® for both detecting current renal function and monitoring renal (dys)function in kidney transplant patients was examined. Methods: Accuracy of the StatSensor® with capillary and venous whole blood was evaluated and compared to an isotopic dilution mass spectrometry (IDMS)-traceable enzymatic creatinine test in venous serum (n=138). Twenty Li-heparin samples were compared to the IDMS reference method performed by a Joint Committee for Traceability in Laboratory Medicine (JCTLM)-listed reference laboratory (RfB, Bonn, Germany). To evaluate StatSensor®'s suitability to monitor kidney function, both venous and capillary samples were obtained in 20 hospitalized transplantation patients. Venous samples were analyzed with an IDMS-traceable enzymatic test, capillary samples were measured using the StatSensor®. For all 2-day intervals, percentage change in creatinine was compared between both methods. Results: The StatSensor® did not meet total allowable error criterion of 6.9%. Average overall CVa for the StatSensor® was 10.4% and 5.2% for capillary and venous whole blood results, respectively. Overall CVa for the central laboratory serum creatinine method was

The concept of measurement traceability provides probably the most important strategy to achieve standardization in laboratory medicine aimed at comparable measurement results regardless of the method, the measurement procedure (test kit) and of the laboratory where analyses are carried out. Establishing networks of reference laboratories is - in addition to reference measurement procedures and reference materials - one of the biggest challenges in implementing the concept of measurement traceability. With respect to these requirements, the Joint Committee on Traceability in Laboratory Medicine (JCTLM), established by the BIPM, the IFCC and the ILAC, has launched two projects in its working groups. WG-1 has to date published tables of reference materials and reference procedures on the BIPM web-sites, whereas WG-2 is identifying reference measurement laboratories. There is general agreement now that reference laboratories should be identified - according to the metrological level of the procedures applied where the principle of measurement is the most important criterion, - on the basis of accreditation or at least compliance with ISO 15195 or ISO 17025 as calibration laboratory, and - on the basis of their ability to demonstrate performance in regular inter - laboratory comparisons (ring trials). To date, a data base on candidate reference laboratories has been collected containing information on the laboratory identity, the metrological level of the procedures and on the status of accreditation and the participation in networks or ring trials. The data base currently contains the addresses of about 60 laboratories. On average, each of the laboratories reported measurement capabilities for six different measurands resulting in about 360 entries. The IFCC has recently launched a ring trial program for reference laboratories for some thirty different measurands. Ring trial results not only demonstrate the competence of individual laboratories, but also reveal the equivalence or bias of different reference procedures. .

Dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) are suggested to be important neurosteroids. We investigated steroid sulfatase (STS) in human temporal lobe biopsies in the context of possible cerebral DHEA(S) de novo biosynthesis. Formation of DHEA(S) in mature human brain tissue has not yet been studied. 17α-Hydroxylase/C17-20-lyase and hydroxysteroid sulfotransferase catalyze the formation of DHEA from pregnenolone and the subsequent sulfoconjugation, respectively. Neither their mRNA nor activity were detected, indicating that DHEA(S) are not produced within the human temporal lobe. Conversely, strong activity and mRNA expression of DHEAS desulfating STS was found, twice as high in cerebral neocortex than in subcortical white matter. Cerebral STS resembled the characteristics of the known placental enzyme. Immunohistochemistry revealed STS in adult cortical neurons as well as in fetal and adult Cajal-Retzius cells. Organic anion transporting proteins OATP-A, -B, -D, and -E showed high mRNA expression levels with distinct patterns in cerebral neocortex and subcortical white matter. Although it is not clear whether they are expressed at the blood–brain barrier and facilitate an influx rather than an efflux, they might well be involved in the transport of steroid sulfates from the blood. Therefore, we hypothesize that DHEAS and/or other sulfated 3β-hydroxysteroids might enter the human temporal lobe from the circulation where they would be readily converted via neuronal STS activity.

Measurement traceability is probably the most important tool for achievement of comparability in clinical chemistry. As stipulated by the In Vitro Diagnostica Directive of the European Union and several ISO standards, values assigned to calibrators and control materials must be traceable to reference materials and/or reference procedures of higher order. In the German proficiency testing system, statutory use of reference measurement procedures for several measurands has been in force since 1988. As a result, reference procedures are now regularly applied for the setting up of target values in the control samples of internal and external quality assessment and for assigning values to the manufacturer's calibrator and control materials. Noticeably, the comparability of results obtained by different diagnostic tests has greatly improved for the measurement of many metabolites and substrates, e.g. creatinine, cholesterol, uric acid, total glycerol and urea. For many measurands in laboratory medicine the implementation of the concept of traceability proves to be much more difficult; this mainly concerns the measurement of proteins, in particular enzymes, proteo-hormones, tumour markers and cardiac markers. For such measurands the analyte must first of all be distinctively defined before a reference system can be established which comprises reference procedures, reference materials and networks of reference laboratories.

Dehydroepiandrosterone and its sulphate are important factors for vitality, development and functions of the CNS. They were found to be subjects to a series of enzyme-mediated conversions within the rodent CNS. In the present study, we were able to demonstrate for the first time that membrane-associated dehydroepiandrosterone 7α-hydroxylase activity occurs within the human brain. The cytochrome P450 enzyme demonstrated a sharp pH optimum between 7.5 and 8.0 and a mean KM value of 5.4 µm, corresponding with the presence of the oxysterol 7α-hydroxylase CYP7B1. Real-time RT–PCR analysis verified high levels of CYP7B1 mRNA expression in the human CNS. The additionally observed conversion of dehydroepiandrosterone via cytosolic 17β-hydroxysteroid dehydrogenase activity could be ascribed to the activity of an enzyme with a broad pH optimum and an undetectably high KM value. Subsequent experiments with cerebral neocortex and subcortical white matter specimens revealed that 7α-hydroxylase activity is significantly higher in the cerebral neocortex than in the subcortical white matter (p

Background: The efficacy of traditional Chinese medicine (TCM) as a treatment for atopic dermatitis has been evaluated in clinical trials. Until now, the underlying mechanism of this treatment has remained completely elusive; this is particularly true of its putative effects on dendritic cells (DCs), which might play a pivotal role in the disease. Objective: We investigated the influence of a standardized extract from 10 Chinese herbs that was successfully used in clinical trials on the generation of monocyte-derived DCs from atopic donors. Methods: Detailed phenotypic and functional exploration of DCs generated in the presence of IL-4 and GM-CSF and treated with different concentrations of TCM or a placebo control was performed. Results: TCM profoundly affected the morphology and phenotype of the developing DCs. They lost their typical dendritic morphology and decreased their expression of CD1a as well as the low-affinity IgE receptor CD23. Most importantly, TCM-exposed DCs exhibited a diminished stimulatory activity toward autologous antigen-specific and allogeneic T cells while secreting high amounts of IL-10. Conclusion: TCM induces immunopharmacologic alterations on DCs from atopic donors in vitro. These alterations might account, at least in part, for the therapeutic effect of this treatment in AD in vivo. (J Allergy Clin Immunol 2001;108:588-93.)

The new version of ISO Guide 34 requires producers of certified reference materials (CRMs) to include contributions of possible instability to the overall CRM uncertainty, to obtain a value for the uncertainty in compliance with the Guide to the Expression of the Uncertainty in Measurement (GUM). A pragmatic approach to estimating the uncertainty of stability is presented. It relies on regression analysis of stability data with subsequent testing of the slope of the regression line for significance. If the slope is found to be statistically insignificant, a shelf life is chosen and the uncertainty connected with this time is estimated via the standard deviation of the slope. This uncertainty is included in the overall uncertainty of the CRM. This approach is explained with examples showing its applicability to matrix CRMs.

Uncertainties of four enzyme-CRMs that have recently been certified in a co-operation between the IRMM and the International Federation for Clinical Chemistry were estimated. Estimation was based on the sum of the uncertainties of characterization, homogeneity and stability. Data from the certification collaborative study were used to estimate laboratory uncertainties, which form the basis for the uncertainty of characterization. Estimations for the uncertainty of homogeneity were derived from classical homogeneity studies. The estimations of uncertainty of stability caused the most difficulties. Realistic uncertainties fitting the needs of customers while being derived from measurement data based on theoretical considerations were obtained.

Background: A reference measurement procedure is needed to demonstrate the traceability of results of urea measurements in human serum. We developed a measurement procedure using the principle of isotope dilution gas chromatography/mass spectrometry. Methods: [13C,15N2]Urea as internal standard was added to a serum sample and equilibrated with endogenous nonlabeled urea. For the preparation of calibrators, the same amount of labeled urea was mixed with known amounts of nonlabeled urea. The serum samples were treated with ethanol to remove proteins by precipitation. The labeled and nonlabeled urea of the samples was converted into a trimethylsilyl derivative of 2-hydroxypyrimidine. The gas chromatography/mass spectrometry system was adjusted to monitor m/z 153 and 168 for the nonlabeled urea derivative and m/z 156 and 171 for the isotopically labeled analogs. The results of the determination were calculated from peak ratios by a hyperbolic calculation function based on the theory of isotope dilution analysis. Results: The procedure was applied to control samples and patient samples and evaluated with respect to its trueness and precision. The standard uncertainty of the results was 0.47–1.72%. Conclusions:This reference measurement procedure allows values to be assigned to controls and calibrators that are traceable to the primary urea reference material of NIST and, therefore, to the Système International unit “mole” with a low degree of uncertainty. This procedure provides a tool for the highly accurate determination of urea in control materials as well as in patient sera.

OBJECTIVES: A new method for the quantitative determination of 17alpha-ethinylestradiol-17beta (EE2) in serum is presented here based on the principle of isotope dilution mass spectrometry (IDMS) with [13C]EE2 as internal standard. The technique was used to determine the concentration profiles of EE2 in the serum of female subjects who had taken oral contraceptives with different progestin components. The method has proved to be very reliable with respect to trueness, specificity, precision and detection sensitivity and offers considerable advantages compared with the immunological methods of measurement used to date. STUDY DESIGN: Forty-seven female volunteers took two different oral contraceptives containing EE2 combined with different progestins in accordance with a cross-over design. After the administration of 30 microg EE2 combined with 75 microg gestodene (EE2/GSD) or 150 microg desogestrel (EE2/DES), blood samples were taken from the subjects on certain days and in certain previously specified cycles in the course of 12 h after medication. RESULTS AND CONCLUSIONS: The biometric analysis of the results showed that the concentration profiles of EE2 were in their statistics, significantly equivalent after the administration of either of the two oral contraceptives. The sometimes contradictory results found in former studies after the administration of the different contraceptives were presumably due to the methodological shortcomings of the radioimmunological measurement technique. With the use of the highly accurate and specific technique of IDMS it can now be unequivocally established that the different progestins in the tested oral contraceptives have no influence on the bioavailability of EE2 (area under EE2 serum concentration curves, as usually defined in pharmacokinetics).

Background : A multicenter study conducted in Southeast Asia to derive reference intervals (RIs) for 72 commonly measured analytes (general chemistry, inflammatory markers, hormones, etc.) featured centralized measurement to clearly detect regionality in test results. The results of 31 standardized analytes are reported, with the remaining analytes presented in the next report. Method : The study included 63 clinical laboratories from South Korea, China, Vietnam, Malaysia, Indonesia, and seven areas in Japan. A total of 3541 healthy individuals aged 20 – 65 years (Japan 2082, others 1459) were recruited mostly from hospital workers using a well-defined common protocol. All serum specimens were transported to Tokyo at − 80 ° C and collectively measured using reagents from four manufacturers. Three-level nested ANOVA was used to quantitate variation (SD) of test results due to region, sex, and age. A ratio of SD for a given factor over residual SD (representing net between-individual variations) (SDR) exceeding 0.3 was considered significant. Traceability of RIs was ensured by recalibration using value-assigned reference materials. RIs were derived parametrically. Results : SDRs for sex and age were significant for 19 and 16 analytes, respectively. Regional difference was significant for 11 analytes, including high density lipoprotein (HDL)-cholesterol and inflammatory markers. However, when the data were limited to those from Japan, regionality was not observed in any of the analytes. Accordingly, RIs were derived with or without partition by sex and region. Conclusions : RIs applicable to a wide area in Asia were established for the majority of analytes with traceability to reference measuring systems, whereas regional partitioning was required for RIs of the other analytes.

We describe an External Quality Assessment Scheme (EQAS) intended for reference (calibration) laboratories in laboratory medicine and supervised by the Scientific Division of the International Federation of Clinical Chemistry and Laboratory Medicine and the responsible Committee on Traceability in Laboratory Medicine. The official EQAS website, RELA (www.dgkl-rfb.de:81), is open to interested parties. Information on all requirements for participation and results of surveys are published annually. As an additional feature, the identity of every participant in relation to the respective results is disclosed. The results of various groups of measurands (metabolites and substrates, enzymes, electrolytes, glycated hemoglobins, proteins, hormones, thyroid hormones, therapeutic drugs) are discussed in detail. The RELA system supports reference measurement laboratories preparing for accreditation according to ISO 17025 and ISO 15195. Participation in a scheme such as RELA is one of the requirements for listing of the services of a calibration laboratory by the Joint Committee on Traceability in Laboratory Medicine.

The concept of measurement traceability provides the most important strategy in achieving standardization in laboratory medicine aimed at equivalent measurement results regardless of the principle of measurement, the method, the actual measurement procedure (test kit) and the laboratory where analyses are carried out.

Summary OBJECTIVE No satisfactory treatment for adrenocortical carcinoma (ACC) is available. We investigated the efficacy and toxicity of suramin In the treatment of metastatic ACC since suramin has been recently reported to be active as a single agent therapy for patients with ACC and prostatic carcinoma. DESIGN We collected data on 9 patients with metastatic ACC treated with suramin in four centres in Germany between 1987 and 1992. PATIENTS Nine patients (5 women, 4 men; age range 32–67 years) were included. Biochemical evidence of steroid excess was found in 6/9, in three leading to clinical symptoms (hypertension, hyperglycaemla, hirsutism, gynaecomastia). MEASUREMENTS Tumour responses were assessed by radiological and biochemical evaluation. Other investigations included regular measurements of blood cell counts, coagulation, hepatic and renal function parameters, and serum suramin concentrations. RESULTS The patients received cumulative doses ranging from.2 to 30·2 g suramin over periods of 1–15 months. 3/9 achieved a partial response, 2/9 disease stabilization and 4/9 experienced progressive disease. Tumour responses were transient. Suramin treatment was without direct influence on steroid excess. Serious side-effects included coagulopathy (6/9), thrombocytopenla (6/9), polyneuropathy (2/9) and allergic skin reactions (4/9); the death of two patients was possibly related to suramin therapy. Both toxicity and tumour response were strongly associated with serum level or cumulative dose of suramin. CONCLUSIONS (1) Suramin is of antineoplastic efficacy in the treatment of metastatic adrenocortical carcinoma. (2) The clinical use of suramln is limited by a narrow therapeutic window with the risk of serious and possibly lethal toxicity at one extreme, and loss of efficacy at the other. Strict monitoring of suramin serum levels is mandatory aiming at levels between 200 and 250mg/l. Suramin should not be considered as first-line treatment for metastatic adrenocortical carcinoma. (3) To improve treatment options in adrenocortical carcinoma as well as for further investigation on the usefulness of suramin, controlled prospective trials are urgently needed.

African sleeping sickness (SS) is a severe, potentially lethal parasitic disease. The treatments of choice are the antiparasitic agents suramin, which is adrenotoxic, and/or melarsoprol. We evaluated the functional integrity of the hypothalamic-pituitary-adrenal (HPA) axis of patient with SS before, during, and after therapy with suramin and/or melarsoprol, in two sequential stages. First, we employed the standard adrenocorticotropic hormone (ACTH) 1-24 stimulation test (250 µg i.v.) to assess the maximal adrenocortical responsiveness of 69 patients with SS and 38 normal controls. We demonstrated paradoxically subnormal Cortisol responses before suramin therapy [net Cortisol response 60 min after stimulation: 10.5 ± 2.9 (mean ± SE) vs. 17.5 ± 1.0 µg/dl for controls, p = 0.004], with 27% of the patients falling within the adrenal insufficiency range (stimulated cortisol concentration

As has been demonstrated, mass spectrometry provides a powerful analytical tool for the accurate measurement of small amounts of substances in a complex biological matrix. In our laboratory this technique is used as a reference method for measuring the routine clinical chemical parameters creatinine, uric acid, cholesterol, total glycerol and the hormones cortisol, testosterone, oestradiol-17β, oestriol, progesterone, aldosterone and thyroxine in human serum. In general, the analytical procedure for measuring a substance by isotope dilution mass spectrometry (IDMS) consists of the following steps: The methods described here are now routinely in use for the quality control scheme of the Deutsche Gesellschaft fur Klinische Chemie for assessing target values in external quality control sera. The reference method values obtained by IDMS provide a reliable basis for evaluating and comparing the results of collaborative surveys.

In addition to reference measurement procedures and reference materials, reference or calibration laboratories play an integral role in the implementation of measurement traceability in routine laboratories. They provide results of measurements using higher-order methods, e.g. isotope dilution mass spectrometry and may assign values to materials to be used for external quality assessment programs and to secondary reference materials. The requirements for listing of laboratories that provide reference measurement services include a statement of the metrological level or principle of measurement, accreditation as a calibration laboratory according to ISO 15195 and the participation in a proficiency testing system (regular inter-laboratory comparisons) for reference laboratories. Ring trials are currently conducted for thirty well-defined measurands and the results are made available to all laboratories. Through the use of reference laboratory services that are listed by the Joint Committee for Traceability in Laboratory Medicine there is the opportunity to further promote traceability and standardisation of laboratory measurements.

Context.—Harmonization and standardization of results among different clinical laboratories is necessary for clinical practice guidelines to be established. Objective.—To evaluate the state of the art in measuring 10 routine chemistry analytes. Design.—A specimen prepared as off-the-clot pooled sera and 4 conventionally prepared specimens were sent to participants in the College of American Pathologists Chemistry Survey. Analyte concentrations were assigned by reference measurement procedures. Participants.—Approximately 6000 clinical laboratories. Results.—For glucose, iron, potassium, and uric acid, more than 87.5% of peer groups meet the desirable bias goals based on biologic variability criteria. The remaining 6 analytes had less than 52% of peer groups that met the desirable bias criteria. Conclusions.—Routine measurement procedures for some analytes had acceptable traceability to reference systems. Conventionally prepared proficiency testing specimens were not adequately commutable with a fresh frozen specimen to be used to evaluate trueness of methods compared with a reference measurement procedure.

This paper is the eighth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The concept of reference procedures for the measurement of catalytic activity concentrations of enzymes; Part 2. Reference procedure for the measurement of catalytic concentration of creatine kinase; Part 3. Reference procedure for the measurement of catalytic concentration of lactate dehydrogenase; Part 4. Reference procedure for the measurement of catalytic concentration of alanine aminotransferase Part 5. Reference procedure for the measurement of catalytic concentration of aspartate aminotransferase Part 6. Reference procedure for the measurement of catalytic concentration of gamma-glutamyltransferase; Part 7. Certification of four reference materials for the determination of enzymatic activity of gamma-glutamyltransferase, lactate dehydrogenase, alanine aminotransferase and creatine kinase at 37 degrees C. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on.

This paper is the eighth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37°C and the certification of reference preparations. Other parts deal with: Part 1. The concept of reference procedures for the measurement of catalytic activity concentrations of enzymes; Part 2. Reference procedure for the measurement of catalytic concentration of creatine kinase; Part 3. Reference procedure for the measurement of catalytic concentration of lactate dehydrogenase; Part 4. Reference procedure for the measurement of catalytic concentration of alanine aminotransferase Part 5. Reference procedure for the measurement of catalytic concentration of aspartate aminotransferase Part 6. Reference procedure for the measurement of catalytic concentration of γ-glutamyltransferase; Part 7. Certification of four reference materials for the determination of enzymatic activity of γ-glutamyltransferase, lactate dehydrogenase, alanine aminotransferase and creatine kinase at 37°C. The procedure described here is deduced from the previously described 30°C IFCC reference method. Differences are tabulated and commented on.Clin Chem Lab Med 2006;44:1146–55.

Context.—The National Kidney Disease Education Program recommends calculating glomerular filtration rate from serum creatinine concentration. Accurate creatinine measurements are necessary for this calculation. Objective.—To evaluate the state of the art in measuring serum creatinine, as well as the ability of a proficiency testing program to measure bias for individual laboratories and method peer groups. Design.—A fresh-frozen, off-the-clot pooled serum specimen plus 4 conventional specimens were sent to participants in the College of American Pathologists Chemistry Survey for assay of creatinine. Creatinine concentrations were assigned by isotope dilution mass spectrometry reference measurement procedures. Participants.—Clinical laboratories with an acceptable result for all 5 survey specimens (n = 5624). Results.—The fresh frozen serum (FFS) specimen had a creatinine concentration of 0.902 mg/dL (79.7 μmol/L). Mean bias for 50 instrument-method peer groups varied from −0.06 to 0.31 mg/dL (−5.3 to 27.4 μmol/L), with 30 (60%) of 50 peer groups having significant bias (P < .001). The bias variability was related to instrument manufacturer (P ≤ .001) rather than method type (P = .02) with 24 (63%) of 38 alkaline picric acid methods and with 6 (50%) of 12 enzymatic methods having significant biases. Two conventional specimens had creatinine concentrations of 0.795 and 2.205 mg/dL (70.3 and 194.9 μmol/L) and had apparent survey biases significantly different (P < .001) from that of the FFS specimen for 34 (68%) and 35 (70%) of 50 peer groups, respectively. Conclusions.—Thirty of 50 peer groups had significant bias for creatinine. Bias was primarily associated with instrument manufacturer, not with type of method used. Proficiency testing using a commutable specimen measured participant bias versus a reference measurement procedure and provided trueness surveillance of instrument-method peer groups.

Background: Assuring/demonstrating metrologic traceability of in vitro diagnostics necessitates the availability of measurand-specific reference measurement systems (RMSs) and the possibility for industry to work with competent reference measurement laboratories (RMLs). Here we report the results of a European project to investigate the feasibility of developing a RMS for serum total thyroxine. Methods: Four candidate RMLs (cRMLs) developed/implemented variants of a candidate reference measurement procedure (cRMP) based on isotope dilution–liquid chromatography–mass spectrometry. The sole constraint implemented was calibration with a common thyroxine primary calibrator. The RMPs were externally validated and assessed for comparability in round-robin trials using common samples, i.e., 5 lyophilized and 33 frozen native sera. At the same time, the performance of the cRMLs organized in a network was assessed. For uniform external quality assessment, common performance specifications were agreed on. Results: All cRMLs performed the cRMPs with fulfillment of the predefined specifications: total and between-laboratory CVs ≤2.0% and 2.5%, respectively, and a systematic deviation ≤0.9%, estimated with a target assigned from the mean of means obtained by the cRMLs. The mean expanded uncertainty for value assignment to the native sera was 2.1%. Conclusions: A network of cRMLs, with externally conformed competence to properly perform RMPs, has been established. Performance specifications were defined and will form the basis for admittance of new network members. A serum panel, successfully targeted during the validation process, is available for split-sample measurements with commercial routine measurement procedures. The model can now be used for other measurands for which traceability to the Système International d’Unités is needed.

Dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) are suggested to be important neurosteroids. We investigated steroid sulfatase (STS) in human temporal lobe biopsies in the context of possible cerebral DHEA(S) de novo biosynthesis. Formation of DHEA(S) in mature human brain tissue has not yet been studied. 17 alpha-Hydroxylase/C17-20-lyase and hydroxysteroid sulfotransferase catalyze the formation of DHEA from pregnenolone and the subsequent sulfoconjugation, respectively. Neither their mRNA nor activity were detected, indicating that DHEA(S) are not produced within the human temporal lobe. Conversely, strong activity and mRNA expression of DHEAS desulfating STS was found, twice as high in cerebral neocortex than in subcortical white matter. Cerebral STS resembled the characteristics of the known placental enzyme. Immunohistochemistry revealed STS in adult cortical neurons as well as in fetal and adult Cajal-Retzius cells. Organic anion transporting proteins OATP-A, -B, -D, and -E showed high mRNA expression levels with distinct patterns in cerebral neocortex and subcortical white matter. Although it is not clear whether they are expressed at the blood-brain barrier and facilitate an influx rather than an efflux, they might well be involved in the transport of steroid sulfates from the blood. Therefore, we hypothesize that DHEAS and/or other sulfated 3beta-hydroxysteroids might enter the human temporal lobe from the circulation where they would be readily converted via neuronal STS activity.

Estrogens play a crucial role in multiple functions of the brain and the proper balance of inactive estrone and active estradiol-17beta might be very important for their cerebral effects. The interconversion of estrone and estradiol-17beta in target tissues is known to be catalysed by a number of human 17beta-hydroxysteroid dehydrogenase (17beta-HSD) isoforms. The present study shows that enzyme catalysed interconversion of estrone and estradiol-17beta occurs in the human temporal lobe. The oxidative cerebral pathway preferred estradiol-17beta to Delta(5)-androstenediol and testosterone, whereas the reductive pathway preferred dehydroepiandrosterone (DHEA) to Delta(4)-androstenedione and estrone. An allosteric Hill kinetic for NAD-dependent oxidation of estradiol-17beta was observed, whereas a typical Michaelis-Menten kinetic was shown for NADPH-dependent reduction of estrone. Investigations of the interconversion of estrogens in cerebral neocortex (CX) and subcortical white matter (SC) preparations of brain tissue from 12 women and 10 men revealed no sex-differences, but provide striking evidence for the presence of at least one oxidative membrane-associated 17beta-HSD and one cytosolic enzyme that catalyses both the reductive and the oxidative pathway. Membrane-associated oxidation of estradiol-17beta was shown to be significantly higher in CX than in SC (P

Dehydroepiandrosterone and its sulphate are important factors for vitality, development and functions of the CNS. They were found to be subjects to a series of enzyme-mediated conversions within the rodent CNS. In the present study, we were able to demonstrate for the first time that membrane-associated dehydroepiandrosterone 7alpha-hydroxylase activity occurs within the human brain. The cytochrome P450 enzyme demonstrated a sharp pH optimum between 7.5 and 8.0 and a mean KM value of 5.4 micro m, corresponding with the presence of the oxysterol 7alpha-hydroxylase CYP7B1. Real-time RT-PCR analysis verified high levels of CYP7B1 mRNA expression in the human CNS. The additionally observed conversion of dehydroepiandrosterone via cytosolic 17beta-hydroxysteroid dehydrogenase activity could be ascribed to the activity of an enzyme with a broad pH optimum and an undetectably high KM value. Subsequent experiments with cerebral neocortex and subcortical white matter specimens revealed that 7alpha-hydroxylase activity is significantly higher in the cerebral neocortex than in the subcortical white matter (p0.0005), whereas in the subcortical white matter, 17beta-hydroxysteroid dehydrogenase activity is significantly higher than in the cerebral neocortex (p0.0005). No sex differences were observed. In conclusion, the high levels of CYP7B1 mRNA in brain tissue as well as in a variety of other tissues in combination with the ubiquitous presence of 7alpha-hydroxylase activity in the human temporal lobe led us to assume a neuroprotective function of the enzyme such as regulation of the immune response or counteracting the deleterious effects of neurotoxic glucocorticoids, rather than a distinct brain specific function such as neurostimulation or neuromodulation.

This paper is the fifth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of Gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on in Appendix 3.

This paper is the fourth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of Gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on in Appendix 2.

This paper is the seventh in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase. A document describing the determination of preliminary reference values is also in preparation. The certification of the catalytic activity concentrations as determined by the recently elaborated IFCC primary reference methods at 37 degrees C of four enzyme preparations, namely IRMM/IFCC 452 (gamma-glutamyltransferase), IRMM/IFCC 453 (lactate dehydrogenase 1), IRMM/IFCC 454 (alanine aminotransferase) and IRMM/IFCC 455 (creatine kinase) is described. Homogeneity data were derived from previous results. Stability was assessed using recently obtained data as well as data from previous stability studies. The collaborative study for value assignment was performed under a strict quality control scheme to ensure traceability to the primary reference method. Uncertainty of the materials was assessed in compliance with the Guide to the Expression of Uncertainty in Measurement. The certified values obtained at 37 degrees C are 1.90 microkat/l +/- 0.04 microkat/l (114.1 U/l +/- 2.4 U/l), for gamma-glutamyltransferase, 8.37 microkat/l +/- 0.12 microkat/l (502 U/l +/- 7 U/l), for lactate dehydrogenase 1, 3.09 microkat/l +/- 0.07 microkat/l (186 U/l +/- 4 U/l), for alanine aminotransferase and 1.68 microkat/l +/- 0.07 microkat/l (101 U/l +/- 4 U/l), for creatine kinase. The materials are intended for internal quality control as well as for the evaluation of test systems as required by recent European Union legislation. Furthermore, the materials can be used to transfer accuracy from a reference method to a routine procedure provided the procedures exhibit the same analytical specificity and the certified materials are commutable.

This paper is the second in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary reference values is also in preparation. The pro- described 30 degrees C IFCC reference method (1). Differences are tabulated and commented on in Appendix 3.

This paper is the fourth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of Gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on in Appendix 2.

This paper is the seventh in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase. A document describing the determination of preliminary reference values is also in preparation. The certification of the catalytic activity concentrations as determined by the recently elaborated IFCC primary reference methods at 37 degrees C of four enzyme preparations, namely IRMM/IFCC 452 (gamma-glutamyltransferase), IRMM/IFCC 453 (lactate dehydrogenase 1), IRMM/IFCC 454 (alanine aminotransferase) and IRMM/IFCC 455 (creatine kinase) is described. Homogeneity data were derived from previous results. Stability was assessed using recently obtained data as well as data from previous stability studies. The collaborative study for value assignment was performed under a strict quality control scheme to ensure traceability to the primary reference method. Uncertainty of the materials was assessed in compliance with the Guide to the Expression of Uncertainty in Measurement. The certified values obtained at 37 degrees C are 1.90 microkat/l +/- 0.04 microkat/l (114.1 U/l +/- 2.4 U/l), for gamma-glutamyltransferase, 8.37 microkat/l +/- 0.12 microkat/l (502 U/l +/- 7 U/l), for lactate dehydrogenase 1, 3.09 microkat/l +/- 0.07 microkat/l (186 U/l +/- 4 U/l), for alanine aminotransferase and 1.68 microkat/l +/- 0.07 microkat/l (101 U/l +/- 4 U/l), for creatine kinase. The materials are intended for internal quality control as well as for the evaluation of test systems as required by recent European Union legislation. Furthermore, the materials can be used to transfer accuracy from a reference method to a routine procedure provided the procedures exhibit the same analytical specificity and the certified materials are commutable.

This paper is the third in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials tamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method (1). Differences are tabulated and commented on in Appendix 1.

This paper is the first in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and with the certification of reference preparations. Other parts deal with: Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic fication of Four Reference Materials for the Determination of Enzymatic Activity of y-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary reference values is also in preparation.

The goal of standardization for measurements of catalytic concentrations of enzymes is to achieve comparable results in human samples, independent of the reagent kits, instruments and laboratory where the procedure is carried out. To pursue this objective, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) has launched a project to establish a reference system in clinical enzymology. This system is based on three hinges: a) extensively evaluated and carefully described reference procedures, b) certified reference materials and c) a network of reference laboratories operating in a highly controlled manner. The original IFCC-recommended procedures for alanine aminotransferase, aspartate aminotransferase, creatine kinase, gamma-glutamyltransferase, lactate dehydrogenase and alpha-amylase have been slightly modified to optimize them at 37 degrees C, with the definition of detailed operating procedures. A group of laboratories perform these procedures manually, with self-made reagents on carefully calibrated instruments. Partially purified and stabilized materials, prepared in the past by the Community Bureau of Reference, have been re-certified by these laboratories for alanine aminotransferase, creatine kinase, gamma-glutamyltransferase and lactate dehydrogenase activities. Using these materials and the manufacturer's standing procedures, industry can assign traceable values to commercial calibrators. Thus, clinical laboratories, which will use routine procedures with these validated calibrators to measure human specimens, can finally obtain values which are traceable to reference procedures.

Oral dehydroepiandrosterone (DHEA) replacement therapy may have a multitude of potential beneficial effects and exerts its action mainly via peripheral bioconversion to androgens (and estrogens). A daily dose of 50-mg DHEA has been shown by us and others to restore low endogenous serum DHEA concentrations to normal youthful levels followed by an increase in circulating androgens and estrogens. As the hepatic first-pass effect may lead to a non physiological metabolism of DHEA after oral ingestion we studied the influence of two single DHEA doses (50 and 100 mg) on the excretion of steroid metabolites in 14 elderly males [age 58.8+/-5.1 years (mean +/- SEM)] with endogenous DHEAS levels1500 ng/ml and in 9 healthy females (age 23.3+/-4.1 years) with transient suppression of endogenous DHEA secretion induced by dexamethasone (dex) pretreatment (4x0.5 mg/day/4 days). Urinary steroid profiles in the elderly males were compared to the steroid patterns found in 15 healthy young men (age 28.9+/-5.1 years). In the females the results were compared to their individual baseline excretion without dex pretreatment. Urinary steroid determinations were carried out by semiautomatic capillary gas-liquid chromatography. In both genders DHEA administration induced significant increases in urinary DHEA (females: baseline vs. 50 mg vs. 100 mg: 361+/-131 vs. 510+/-264 vs. 1541+/-587 microg/day; males: placebo vs. 50 mg vs. 100 mg: 434+/-154 vs. 1174+/-309 vs. 4751+/-1059 microg/day) as well as in the major DHEA metabolites androsterone (A) and etiocholanolone (Et). Fifty mg DHEA led to an excretion of DHEA and its metabolites only slightly above baseline levels found in young females and in young men, respectively, whereas 100 mg induced clearly supraphysiological values. After 50 mg DHEA the ratios of urinary DHEA metabolites (A/DHEA, Et/DHEA) were not significantly different between elderly males vs. young male volunteers and young healthy females versus their individual baseline levels. In conclusion, an oral dose of 30 to 50 mg DHEA restores a physiological urinary steroid profile in subjects with DHEA deficiency without evidence for a relevant hepatic first-pass effect on urinary metabolites.

The broad objectives of this report are to enhance the clinical utility of the results of hapten measurement immunoprocedures by encouraging standardization of the procedures. It was decided to restrict the subject of the report to one analyte, and cortisol was chosen because of its diagnostic importance, the need for improved comparability with routine procedures, and its relevance to many other analytes. Therefore, the immediate objectives are to improve the clinical utility of total serum cortisol concentrations measured on different occasions and in different laboratories, to make diagnostic reference intervals more reliable and widely applicable, and to improve diagnostic accuracy by: Improving the agreement between results from reference measurement procedures and the results obtained with normal routine immunoprocedures for the measurement of total serum cortisol, and hence the comparability of routine results; and Reducing the susceptibility of the immunoprocedures to crossreactivity and interference. It is recognized that good comparability of results depends on procedures which are specific, properly calibrated and validated, and that the most important factors are resistance to crossreactants and interferants. Analytical goals for cortisol immunoprocedures are zero bias for 'all' samples with respect to a reference procedures, with the total analytical standard deviation equal to, or less than, half the within-individual standard deviation for cortisol, or 7.6% according to a recent estimate. To these ends the group proposes the following measures: 1. An international network of reference laboratories for cortisol measurement should be established, and progressively developed to include other hapten analytes. The service of the participating laboratories would be necessary to make feasible other recommendations listed below. 2. Procedures should be comprehensively validated, including a thorough crossreactivity study with the results presented to indicate the possible significance of each crossreactivity, a direct comparison of results with those obtained by a reference procedure for an adequate number of varied fresh/frozen patient samples, and suitable clinical validation studies. 3. External quality assessment schemes should assess participating laboratory performance against reference procedure values, and not consensus values related to values determined by any group of participating procedures. They should also assess the ability to determine added standard and to resist common interferants. 4. Master calibrators for use in the production of calibrators included in commercial kits, and formulated identically to these, should be certified with at least one reference measurement procedure, so that the concentrations of analyte in calibrators can be traced back to concentrations determined by a reference procedure.(ABSTRACT TRUNCATED AT 400 WORDS)

Wahrend der vergangenen 20 Jahre ist eine Vielzahl neuer Verfahren in das tagliche Arbeitsprogramm klinisch-chemischer Routinelaboratorien eingefuhrt worden. Die meisten dieser Methoden zeichnen sich durch eine hohe Praktikabilitat aus. Die Einfuhrung vorgefertigter Reagenziensatze und mechanisierter Analysengerate machen es moglich, in immer kurzerer Zeit immer mehr klinisch- chemische Routineanalysen durchzufuhren.

In internal and external quality assessment of clinical chemical analyses, the use of reference method values is prescribed in the Federal Republic of Germany as a measure of accuracy control. In the field of lipid analyses, reference methods are available for measuring total cholesterol and total glycerol in control sera. The reference measurement procedures are based on the highly accurate analytical principle of isotope dilution mass spectrometry. A very detailed protocol that ensures a high level of reliability must be followed when reference measurement procedures are carried out. The introduction of reference methods as a basis for accuracy control has greatly limited the unacceptable use of inaccurate routine methods.

In the years 1977 to 1981, 14 quality-control surveys for the determination of steroid hormones were performed in cooperation with the Deutsche Gesellschaft fur Klinische Chemie. Hereby the laboratories participating could in each case analyze the following steroids: aldosterone, cortisol, oestradiol-17 beta, oestriol, progesterone, and testosterone. In the light of the results an investigation was made as to whether, in the course of time, an improvement in the accuracy or in the precision of the determinations had been attained, and to what extent the determinations depend on the qualities of the test material. A clear improvement in the accuracy of the results of the analyses could only be ascertained for oestradiol-17 beta. For aldosterone and cortisol, values were found in pool-plasma whose medians were significantly above the definitive values. An improvement in precision could be noted especially with oestradiol-17 beta and to lesser degrees with cortisol and oestriol. The kind of test material--plasma which contained only the hormones to be analyzed on the one hand, and, on the other hand, pool-plasma, which also contained all endogenous hormones--had no influence on the precision of the results from various laboratories. Low concentrations of the individual steroids led--on the basis of the methodological principle of radioimmunoassays--in almost all cases to a reduced interlaboratory precision in regard to values. The accuracy of the analysis values was considerably impaired only with aldosterone and oestradiol-17 beta by low concentrations: the medians here were in part twice as high as the definitive values.

It has recently been shown that mass fragmentography may serve as a powerful tool in the field of steroid biochemistry. This is demonstrated by the following examples. When [4- 14 C]oestriol was incubated with liver slices of wild mice, about 50 ng of a polar radioactive metabolite were isolated. Despite the small amount of steroid and impurities present in the extract, the unknown metabolite was identified as 6-hydroxyoestriol by the technique of single ion monitoring, using g.l.c. columns of different polarity. Furthermore, mass fragmentography provides a simple and highly specific method for the determination of steroid hormones in body fluids. Using the single ion technique, the amount of steroid is calculated by comparing the peak areas of the sample and of the standard. This method can be considerably improved by the use of steroids labelled with stable or radioactive isotopes as internal standards. The determination is performed by comparing the peak areas of the steroid to be quantitated and of the isotopically labelled steroid; measurement of the peaks is achieved by monitoring two m/e values simultaneously (multiple ion detection). This procedure has been applied to the specific determination of oestrogens, testosterone, aldosterone and tetrahydroaldosterone in plasma and/or urine. The sensitivity of mass fragmentography can be increased by using the heptafluorobutyric esters of the various steroids.

The highly specific and accurate technique of isotope dilution mass spectrometry has been used for the measurement of 17 alpha-ethynyloestradiol-17 beta and norethisterone in serum. Serum samples were obtained from female volunteers who received 2.5 mg lynestrenol and 50 micrograms 17 alpha-ethynyloestradiol-17 beta in two different galenical preparations. The determination of total 17 alpha-ethynyloestradiol-17 beta (conjugated and non-conjugated) was carried out by the following procedure: (1) adsorption of the steroids from 1 ml serum to Amberlite XAD-2; (2) enzyme hydrolysis of the conjugated steroid; (3) addition of 1 ng [6,7-3H2] 17 alpha-ethynyloestradiol-17 beta as internal standard; (4) column chromatography on Sephadex LH 20; (5) derivative formation with heptafluorobutyric anhydride; (6) isotope dilution mass spectrometry at m/z 474 and 478 using a glass capillary gas-liquid chromatography column. For the measurement of norethisterone, which is the major metabolite of lynestrenol, 1 ng [7-3H]norethisterone was added to 0.5 ml serum. The labelled and the non-labelled steroids were extracted and purified by column chromatography on Sephadex LH 20. The norethisterone was reacted to form the 3-enol-17 beta-trimethylsilyl ether of norethisterone and [3H]norethisterone. For isotope dilution mass spectrometry the derivative was injected into the glass capillary column which was coupled to the mass spectrometer. The instrument was adjusted to m/z 442 and 444, corresponding to the molecular ions of the ether derivatives of norethisterone and [7-3H]norethisterone. Accuracy was achieved by the use of highly specific technique of mass spectrometry and the exact control of recovery using the isotope dilution principle. The precision was 4.5% (CV) for the determination of 17 alpha-ethynyloestradiol-17 beta and 2.5% (CV) for norethisterone. The lower limit of detection was at 20 pg ml-1 for both methods.

After incubation of [7- 3 H]-16-dehydroprogesterone with the liver microsomal fraction of male Wistar rats, two radioactive metabolites were isolated and subsequently identified by gas liquid chromatography-mass spectrometry (g.l.c.-m.s.) as 16 α ,17-epoxy-3 β -hydroxy-5 α -pregnan-20-one and 16 α ,17-epoxy-progesterone. In addition to the epoxides, the following two Δ 16 -steroids were isolated: 3 β -hydroxy-5 α -pregn-16-en-20-one and 5 α -pregn-16-ene-3,20-dione. The 16 α ,17-epoxides of C 21 -steroids are relatively stable compounds in contrast to the 16 α ,17 α -epoxides of C 18 - and C 19 -steroids which are rapidly hydrolysed to trans-glycols in the presence of microsomes. Thus, after 30 min of incubation with rat liver microsomes, only 5% of tritiated 16 α ,17-epoxyprogesterone was metabolised; evidence was obtained that the reaction product was identical with 16 β -hydroxyprogesterone, indicating that in the series of C 21 -steroids a reduction of the epoxide group takes place rather than a hydrolysis.

4,16-Androstadien-3-one was incubated with the microsomal fraction of male rat liver in the presence of a NADPH generating system and oxygen. The metabolites formed were extracted from the incubation medium and purified by thin-layer chromatography (tic). Final identification was performed by combined gas liquid chromatography-mass spectrometry. Incubation of 4,16-androstadien-3-one resulted in the formation of a non-polar metabolite which proved to be 16α,17α-epoxy-4-androsten-3-one. This epoxide is a shortlived intermediate which is rapidly hydrolysed by the microsomal epoxide hydratase to 16β,17α-dihydroxy-4-androsten-3-one. In order to increase the amounts of epoxide in the incubation mixtures, styrene oxide which is a potent inhibitor of the epoxide hydratase was added. Under these conditions, up to 8% of the 16-dehydro-steroid incubated was transferred to the 16α,17α-epoxy-compound.

Isotope dilution-mass spectrometry (ID-MS) is a reliable analytical tool for the highly accurate measurement of volatile compounds in biological fluids. In the present investigation the technique of ID-MS has been applied to the specific and accurate determination of oestradiol-17β, oestriol, testosterone, progesterone, aldosterone and cortisol in human serum. The analytical procedure for the measurement of steroid hormones comprises the following steps: (1) addition of a 14C-labelled steroid to the serum sample; (2) extraction of the 14C-labelled and of the non-labelled steroid by the use of an organic solvent; (3) purification of the steroid fraction by column chromatography on Sephadex LH-20 or on Lipidex-5000; (4) formation of a derivative; (5) combined gas chromatography-mass spectrometry. During gas chromatography the mass spectrometer continuously records two m/e values corresponding to the labelled and the non-labelled hormone. Quantitative determination is performed by comparing the peak heights of the hormone to be determined and of the labelled internal standard. The accuracy of the methods is based on the high specificity of mass spectrometry and on the exact control of recovery employing the principle of isotope dilution. Therefore, the analytical procedures described here may be recommended as definitive methods in clinical chemistry.

Mass fragmentography may serve as a powerful tool in the fields of steroid biochemistry and clinical chemistry; it provides a simple and highly specific method for the determination of steroids in body fluids. Isotopically labelled steroids, corresponding to the natural occurring steroids, may be used as internal standards in order to correct for procedural losses as well as adsorption effects on the gas Chromatographie columns. Since the mass spectrometer is capable of separating isotopes, quantitative determinations may be performed by comparing the peak areas of the unlabelled and the isotopically labelled steroids; the peaks are recorded simultaneously by monitoring two m/e- values (multiple ion detection). With respect to sensitivity and specificity, the method may be considerably improved by the use of special derivatives, e.g. heptafluorobutyrates. Because of their high specificity, determinations by mass fragmentography will be increasingly used as reference methods in the field of steroid hormones. In the present paper the procedure has been applied to the specific determination of oestrogens, testosterone, 5α-dihydrotestosterone, cortisol and aldosterone in human plasma.

SUMMARY It has recently been shown that mass fragmentography may serve as a powerful tool in the field of steroid biochemistry. This is demonstrated by the following examples. When [4-14C]oestriol was incubated with liver slices of wild mice, about 50 ng of a polar radioactive metabolite were isolated. Despite the small amount of steroid and impurities present in the extract, the unknown metabolite was identified as 6-hydroxyoestriol by the technique of single ion monitoring, using g.l.c. columns of different polarity. Furthermore, mass fragmentography provides a simple and highly specific method for the determination of steroid hormones in body fluids. Using the single ion technique, the amount of steroid is calculated by comparing the peak areas of the sample and of the standard. This method can be considerably improved by the use of steroids labelled with stable or radioactive isotopes as internal standards. The determination is performed by comparing the peak areas of the steroid to be quantitated and of the isotopically labelled steroid: measurement of the peaks is achieved by monitoring two m/e values simultaneously (multiple ion detection). This procedure has been applied to the specific determination of oestrogens, testosterone, aldosterone and tetrahydroaldosterone in plasma and/or urine. The sensitivity of mass fragmentography can be increased by using the heptafluorobutyric esters of the various steroids.