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Biomedical subjects

S J Gaskell

Publications and source records attributed to S J Gaskell.

108 records · Page 6Linked to original sources
PubMed1980

A simple direct solid-phase enzymeimmunoassay for cortisol in plasma.

A simple, direct solid-phase enzyme-labelled immunoassay for plasma cortisol was established using horseradish peroxidase/cortisol 21-hemisuccinate conjugate as "enzyme label. The antiserum, raised against a cortisol 21-hemisuccinate/bovine serum albumin conjugate, was coupled to cellulose to facilitate separation of free and bound steroid. Solvent extraction was avoided by the use of heat denaturation of the cortisol-binding globulin. This assay had a lower limit of sensitivity of 16.6 nmol/l and satisfied the standard criteria of accuracy and precision. Cortisol concentrations determined by enzymeimmunoassay were in excellent agreement with a gas liquid chromatography/mass spectrometry procedure (r=0.98, n=19) and also with the radioimmunoassay in current use (r=0.95, n=20). Cortisol levels after ACTH stimulatin and dexamethasone suppression in various subjects are presented. This enzymeimmunoassay is particularly applicable to the routine determination of plasma cortisol in small clinical laboratories or in those with a fluctuating workload.

Adrenocorticotropic Hormone↗
PubMed1980

Tissue androgen concentrations in golden hamsters with benign prostatic tumours.

Using gas chromatography-high resolution mass spectrometry with selected ion detection, the concentrations of testosterone, 5alpha-dihydrotestosterone, androsterone, 5alpha-androstane-3alpha,17beta-diol, 5alpha-androstane-3beta,17alpha-diol and 5alpha-androstane-3beta,17beta-diol were measured in the dorsal and ventral prostates of two strains of golden hamster (Mesocricetus auratus) at various ages from 60 to 250 days. The tissue concentrations from a control strain were compared with those of the BIO 87.2 strain of hamster, the latter developing benign hyperplasia of the prostate between 90 and 120 days of age. Marked increases in the concentration of total 5alpha-androstanediols in both prostatic lobes of the BIO 87.2 strain were detected, with the highest level of over 345 nmol/g protein being found at 200 days of age. In comparison, the control strain showed a less pronounced increase in concentration at 150 days. Increases in total 5alpha-androstanediols were mainly associated with increases in the concentration of 5alpha-androstane-3alpha,17beta-diol. Concentrations of testosterone in prostatic tissue were also found to increase in the BIO 87.2 animals with peak values being seen at 200 days. Increases in concentration of androsterone were observed by 150 days and these levels were maintained up to 250 days of age. Control animals showed no comparable increases in testosterone and androsterone during the time-course studied. Surprisingly, no significant variation in 5alpha-dihydrotestosterone concentration was detected in either strain from 60 to 250 days although levels were slightly but consistently higher in the BIO 87.2 strain. There were no significant fluctuations in any of the androgens assayed either before or during tumour development. The increases in 5alpha-androstane-3alpha,17beta-diol, testosterone and androsterone were detected only after tumours had become established.

Androgens↗
PubMed1980

Gas chromatography/high-resolution mass spectrometry as a reference method for clomipramine determination.

A method has been developed for the determination of plasma clomipramine levels, based on gas chromatography/high-resolution mass spectrometry. Accuracy and precision have been shown to be excellent in analyses of plasma samples to which known quantities of the drug have been added. In view of the great specificity achieved with high-resolution mass spectrometry, the technique is recommended for reference purposes. There is good agreement between results obtained by a routine radioimmunoassay and this reference method.

Clomipramine↗
PubMed1979

The determination of testosterone in hamster prostate by gas chromatography mass spectrometry with selected metastable peak monitoring.

Quantitative analyses of testosterone, as the methyl oxime t-butyldimethylsilyl ether, are performed by gas chromatography mass spectrometry with selected monitoring of the metastable peak corresponding to the fragmentation [M]+. leads to [M-C4H9]+ in the field free region preceding the electric sector of a double focusing mass spectrometer. A detection limit of c. 30 pg is observed during analyses of the standard compound. The method is applied to the quantitative determination of testosterone in extracts of prostatic tissue from the golden hamster, using epitestosterone as the internal standard. The analytical specificity is similar to that achieved during gas chromatography high resolution mass spectrometry with selected ion detection of [M]+. ions; gas chromatography low resolution mass spectrometry is of inadequate specificity.

Animals↗
PubMed1979

Determination of tamoxifen and an hydroxylated metabolite in plasma from patients with advanced breast cancer using gas chromatography-mass spectrometry.

An assay has been established for the selective measurement of tamoxifen and its monohydroxy derivative, metabolite B, in human plasma. The assay was used to examine the concentrations of these compounds, relative to oestradiol-17 beta, in the plasma of patients undergoing tamoxifen therapy for advanced breast cancer. Oral administration of the drug (20 mg twice a day) raised the level of tamoxifen in plasma to approximately 200 ng/ml 20 days after the commencement of treatment. This level was 3000-fold higher than the corresponding concentration of oestradiol which remained within the range for post-menopausal women. Metabolite B was present in plasma at a much lower concentration than tamoxifen although in considerable excess over oestradiol. The overall results are discussed in relation to the possible mechanism of action of the drug.

Breast Neoplasms↗
PubMed1979

A simple, direct radioimmunoassay for plasma cortisol, featuring a 125I radioligand and a solid-phase separation technique.

A simple, direct radioimmunoassay for cortisol in human serum and plasma is described. An antiserum, raised in sheep to a cortisol-3-(O-carboxymethyl)oxime/bovine serum albumin conjugate, is coupled to microcellulose. No extraction is required because plasma samples and standards are incubated with the antiserum and an 125I radioligand in a low-pH buffer, which denatures cortisol-binding globulins. The assay satisfies accepted validation criteria. In addition, results from the radioimmunoassay compare well with those obtained by a gas chromatographic-mass spectrometric technique (r = 0.968; FRIA = 0.97 FGCMS + 2.0 nmol/L). The latter procedure features the very high intrinsic specificity obtained by selected ion monitoring at high mass-spectrometric resolution (M/deltaM = 8500) with a Varian MAT-731 instrument. The simplicity of the radioimmunoassay procedure, with use of reagents prepared "in house," makes this a very practical and economical assay for use in the medium or large endocrine laboratory.

Chromatography, Gas↗
PubMed1978

Development of a procedure for the assay of an experimental steroid drug in dog plasma.

Studies of the estimation of 16alpha-cyano-3beta-cyclopentyloxypregn-5-en-20-one (an experimental drug) in dog plasma are described. Extraction using a salt/solvent pair (ammonium carbonate/ethyl acetate) is followed by a rapid chromatographic procedure employing Lipidex 5000, which affords a substantially purified fraction. After preparation of the t-butyldimethylsilyloxime, quantification of the drug is performed by selected ion monitoring. The [2H9]cyclopentyloxyl analogue is used as an internal standard. In a preliminary experiment, the advantages (in terms of both sensitivity and selectivity) of the use of an open tubular GLC column are demonstrated.

Animals↗
PubMed1978

Selected metastable peak monitoring: a new specific technique in quantitative gas chromatography mass spectrometry.

Using the combined electrostatic analyser-magnet scan facility of a double focusing mass spectrometer, the daughter ion peak for the fragmentation, [M-57]+ leads to [M-57-76]+, of a 5alpha-dihydrotestosterone tert-butyl-dimethylsilyl ether was monitored during gas chromatography mass spectrometry. The detection limit was approximately 20 pg. The steroid was detected by this method in an extract of human blood plasma.

Chromatography, Gas↗
PubMed1977

Gas-liquid chromatography-mass spectrometry of phospholipid mixtures after enzymic hydrolysis.

Gas-liquid chromatography-mass spectrometry (GLC-MS), employing an open-tubular Silanox-type glass column, has been applied to the products of phospholipase C hydrolysis of natural and synthetic phospholipid mixtures. The materials studied were egg lysolecithin, synthetic L-alpha-l-stearoyl-2-oleoyl lecithin, bovine brain sphingomyelin, and phospholipids derived from human arterial tissue. l-Monoglycerides and ceramides were analysed as methaneboronates, and 1,2-diglycerides as trimethylsilyl ethers. The results indicate the potential value of open-tubular GLC-MS in a rapid procedure for the concurrent analysis of the major classes or polar lipids after enzymic dephosphorylation.

Chromatography, Gas↗
PubMed1976

Applications of boronate derivatives in the study of ceramides by gas-liquid chromatography-mass spectrometry.

Methaneboronate derivatives of ceramides possess excellent gas-liquid chromatographic properties and give informative mass spectra. Molecular ions, present at high abundance where an unsaturated acyl substituent is present, are accompanied in the electron impact mass spectra by fragment ions which denote the acyl group and long-chain base. In the gas-liquid chromatographic-mass spectrometric analyses of natural ceramides, as methaneboronate derivatives, the properties of open-tubular columns are exploited to give good separations in moderate analysis times. An application is made to the analysis of ceramides derived from sphingomyelin of human arterial tissue.

Arteries↗
PubMed1976

New derivatives for the analysis of sphingosine long-chain bases by gas-liquid chromatography-mass spectrometry.

Cyclic derivatives formed by reaction of sphingosines with methane-, n-butane- and benzeneboronic acid have been examined by gas-liquid chromatography (GLC) and by combined GLC-mass spectrometry (MS). Analogous compounds have also been studied, in which the amino group has been protected, for example as an acetone Schiff base or N,N-dimethylaminomethylene derivative. Phytosphingosine (4D-hydroxysphinganine) yielded bis-alkaneboronates. Most of the derivatives were satisfactory for GLC. Molecular ions were apparent (1-100% relative abundance) in all electron impact mass spectra, and and (as [M+1](+)ions) were the base peaks in isobutane chemical ionisation mass spectra.

Arteries↗
PubMed1976

Trimethylsilyl group migration during electron impact and chemical ionization mass spectrometry of the trimethylsilyl ethers of 20-hydroxy-5alpha-pregnan-3-ones and 20-hydroxy-4-pregnen-3-ones.

The electron impact and chemical ionization (isobutane) mass spectra of the TMS derivatives of 20-hydroxy-5alpha-pregnan-3-ones and 20-hydroxy-4-pregnen-3-ones include ions [M--44]+-attributable to loss of a CH3CHO fragment from C-17 with migration of the TMS group to the charge-retaining fragment. Mass spectra of isotopically labelled ([3-18O], [20-18O] and [2H9-TMS]) analogues are consistent with this mechanism; [2H9-TMS] labelling further indicates that subsequent loss of a methyl group from [M--44]+-ions does not involve the TMS group. Corresponding ions are not observed at significant abundance in the spectra of 20beta-trimethylsilyloxy-5alpha-pregnane and 20beta-trimethylsilyloxy-4-pregnen-3-one 3-O-methyloxime. In the electron impact mass spectrum of the t-butyldimethylsilyl ether of 20beta-hydroxy-4-pregnen-3-one, an ion is observed corresponding to loss of 44 atomic mass units from the intense [M--C4H9]+ ion.

Electrochemistry↗