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Biomedical subjects

D G Watson

Publications and source records attributed to D G Watson.

At least 91 records · Page 5Linked to original sources
PubMed1990

Identification and quantitation of phenylalanine, tyrosine and dihydroxyphenylalanine in the thoracic nervous system of the locust, Schistocerca gregaria, by gas chromatography-negative-ion chemical ionisation mass spectrometry.

Phenylalanine, tyrosine and dihydroxyphenylalanine (DOPA) were identified unambiguously and quantitatively determined in single ventral thoracic nerve cords from the locust, Schistocerca gregaria, by gas chromatography-negative-ion chemical ionisation mass spectrometry. Deuterium-labelled analogues of each compound were added to a single ventral thoracic nerve cord in hydrochloric acid; the tissue was homogenised and the suspension centrifuged. The remaining hydrochloric acid was eliminated azeotropically by repeated additions of acetonitrile followed by evaporation under a stream of nitrogen and the resultant residue derivatised by reaction with hexafluoroisopropanol and pentafluoropropionic anhydride. Under negative-ion chemical ionisation conditions, the hexafluoroisopropanol-pentafluoropropionyl derivatives produced characteristic ions which were sufficiently abundant to be suitable for selected-ion monitoring. This method is highly specific and gave a limit of detection below the nanogram level. The amounts of phenylalanine, tyrosine and DOPA in a single ventral thoracic nerve cord were, respectively, 194 +/- 81, 347 +/- 88 and 11 +/- 11 ng per tissue.

Animals↗
PubMed1990

Identification and quantitation of N-acetyl metabolites of biogenic amines in the thoracic nervous system of the locust, Schistocerca gregaria, by gas chromatography-negative-ion chemical ionisation mass spectrometry.

The N-acetylated metabolites of p-tyramine, p-octopamine and dopamine were identified unambiguously and quantitatively determined in a single ventral thoracic nerve cord of the locust, Schistocerca gregaria, by gas chromatography-negative-ion chemical ionisation mass spectrometry (GC-NICIMS). Deuterium-labelled analogues of each compound were added to a single ventral thoracic nerve cord in acetonitrile: the tissue was homogenised and the suspension centrifuged. The solvent was removed from the supernatant and the resultant residue was derivatised with trifluoroacetic anhydride. Under negative-ion chemical ionisation conditions, the trifluoroacetyl derivatives produced ions which were sufficiently abundant to be suitable for selected-ion monitoring. This method is highly specific and gave a limit of detection below the picogram levels. N-Acetyl-5-hydroxytryptamine was determined using a previously published GC-NICIMS technique [S.P. Markey, R.W. Colburn and J.N. Johannessen, Biomed. Mass Spectrom., 7 (1981) 301]. The concentrations of N-acetyltyramine, N-acetyloctopamine, N-acetyldopamine and N-acetyl-5-hydroxytryptamine in locust thoracic nerve cords were, respectively, 1.86 +/- 0.71, 1.13 +/- 0.34, 6.77 +/- 8.48 and 0.07 +/- 0.02 ng per tissue.

Acetic Anhydrides↗
PubMed1990

Dichlorotetrafluoroacetone as a derivatisation reagent in the analysis of mandelic acids in human urine.

Dichlorotetrafluoroacetone has been used to prepare 4-substituted 2-bis (chlorodifluoromethyl)-1,3-dioxolan-5-one derivatives of mandelic acids which were found to be suitable for the analysis of these compounds by gas chromatography-negative-ion chemical ionisation mass spectrometry (GC-NICIMS). The high specificity of the derivatising agent facilitates the identification and quantitation of small amounts of mandelic acids in complex biological matrices. The derivatisation procedure was used to determine the concentrations of m- and p-hydroxymandelic acids and vanillylmandelic acid in to the urine of normal subjects. The method may also have application in the determination of isomeric phenylethylene glycols, the corresponding products of reductive metabolism of biogenic amines.

Acetone↗
PubMed1990

Analysis of biogenic amines and their metabolites in biological tissues and fluids by gas chromatography-negative ion chemical ionization mass spectrometry (GC-NICIMS).

GC-NICIMS has been employed in the analysis of biogenic amines and their metabolites in human urine and human, bovine and porcine aqueous and vitreous humour. Several new chemical derivatization procedures have been developed in order to analyse these compounds. Concentrations of octopamines and synephrines were determined in urine from treated and untreated hypertensive subjects and normotensive individuals; there were no significant differences in concentrations of these metabolites between these groups. Human urine contained several dihydroxy-phenylethylamines which have not been reported as natural metabolites before and also 5- and 6-hydroxydopamine in relatively large amounts. Aqueous and vitreous humour contained very low quantities of noradrenaline, tyramine and dopamine but measurements were inconsistent because sometimes the levels were below the limits of detection. Metabolites of a number of biogenic amines were readily detected in aqueous and vitreous humour.

Animals↗
PubMed1990

The pharmacokinetics of 5-fluorouracil administered by arterial infusion in advanced colorectal hepatic metastases.

The pharmacokinetics of 5-fluorouracil (5FU) following its administration via the hepatic artery in conjunction with biodegradable albumin microspheres and angiotensin II have been studied. Peripheral venous concentrations of 5FU are lower and plasma clearance values higher following intrahepatic arterial administration compared with a similar dose administered by intravenous infusion over both 2 h and 24 h. For the 2 h drug infusions, plasma 5FU concentrations following co-treatment with angiotensin II and microspheres via the hepatic artery were intermediate between those of arterial and venous infusions of 5FU alone. There was a trend towards the peak plasma drug concentrations and the area under the plasma concentration-time curve (AUC) being significantly lower following co-treatment with angiotensin II and microspheres compared with intra-arterial and intravenous infusions of 5FU over 24 h. Co-administration of 5FU, angiotensin II and microspheres via the hepatic artery may reduce drug exposure in the systemic compartment and therefore may increase the therapeutic ratio of 5FU administration via the hepatic artery.

Colorectal Neoplasms↗
PubMed1990

Penetration of synthetic corticosteroids into human aqueous humour.

The penetration of prednisolone acetate (1%) and fluorometholone alcohol (0.1%) into human aqueous humour following topical application was determined using the very sensitive and specific technique of Gas Chromatography with Mass Spectrometry (GCMS). Prednisolone acetate afforded peak mean concentrations of 669.9 ng/ml within two hours and levels of 28.6 ng/ml in aqueous humour were detected almost 24 hours post application. The peak aqueous humour level of fluorometholone was 5.1 ng/ml. The results are compared and contrasted with the absorption of dexamethasone alcohol (0.1%), betamethasone sodium phosphate (0.1%) and prednisolone sodium phosphate (0.5%) into human aqueous humour.

Aged↗
PubMed1990

Penetration of topically applied betamethasone sodium phosphate into human aqueous humour.

Gas Chromatography combined with Negative Chemical Ionisation Mass Spectrometry (GCMS) was used to determine the absorption of topically applied beta-methasone sodium phosphate into the aqueous humour of human subjects undergoing routine intraocular surgery. The Betamethasone concentration was greatest in the interval 91-120 minutes following topical administration (mean peak concentration = 7.7 ng/ml). At twelve hours post instillation the mean concentration of Betamethasone was 2.5 ng/ml and detectable levels were recorded in the aqueous humour 24 hours after application (mean concentration 0.4 ng/ml).

Administration, Topical↗
PubMed1990

Analysis of acidic metabolites of biogenic amines in bovine retina and vitreous and aqueous humour by gas chromatography-negative ion chemical ionisation mass spectrometry.

Acidic metabolites of a number of biogenic amines have been identified and quantified by reaction with either acetic or propionic anhydride in the aqueous phase followed by extraction into ethyl acetate, esterification of carboxyl groups with ditrifluoromethylbenzyl bromide (DTFMBzBr), and then conversion of the remaining free hydroxyl groups to acetates. Subsequent analysis of these derivatives revealed that most (greater than 60%) of the ion current was carried by the ion resulting from the loss of DTFMBz from the molecular ion. This made the method highly specific and practical--limits of detection were established at approximately 200 pg with a potential limit of detection below the picogram level. This method establishes unequivocally that the metabolites of tyramine, dopamine, and adrenaline/noradrenaline (4-hydroxyphenylacetic acid, 3,4-dihydroxyphenylacetic acid, and dihydroxymandelic acid, respectively) are present in bovine retina and in vitreous and aqueous humour. In addition, high concentrations of the dopamine metabolite homovanillic acid were found in retina and vitreous, but not in aqueous humour. p-Hydroxymandelic acid, the acidic metabolite of p-octopamine/p-synephrine, was identified in vitreous and in aqueous humour.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1989

Analysis of biogenic amines in the brain of the American cockroach (Periplaneta americana) by gas chromatography-negative ion chemical ionisation mass spectrometry.

Biogenic amines in the brain of the American cockroach have been identified and quantified by an extraction-derivatisation procedure involving their reaction with ditrifluoromethylbenzoyl chloride (DTFMB) in the aqueous phase followed by extraction into an organic solvent, hydrolysis of phenolic esters and conversion of free hydroxyl groups to trimethylsilyl (TMS) ethers and subsequent analysis by gas chromatography-negative ion chemical ionisation mass spectrometry. The molecular ion of these DTFMB-TMS derivatives carried most of the ion current which made the method highly specific and gave a potential limit of detection below the picogram level. This method establishes unequivocally that the principal amines in cockroach brain are tyramine, p-octopamine, dopamine, 5-hydroxytryptamine and noradrenaline. In contrast to mammalian nervous tissue, the other positional isomers of octopamine, together with the isomeric synephrines, are absent.

Animals↗
PubMed1989

Detection of serotypic variants in viral preparations: sensitivity of a procedure for selection.

The efficiency of an in vitro method (the breakthrough neutralization procedure) for selecting serotypic variants from preparations of human rhinovirus (HRV) 17 and a temperature sensitive strain (Ts-1) of HRV-2 was examined. Viruses were plaqued in the presence of homologous polyclonal antisera, and plaques which escaped neutralization were isolated. For control purposes, isolates were obtained by plaquing in the absence of antisera. Any clone that consistently (minimum of 2 tests) yielded a 4-fold or greater difference in serum neutralization titer compared to the parent virus when tested with antiserum to the parent, was considered a serotypic variant. The efficiency of the breakthrough neutralization procedure was calculated using varying mixtures of 2 related rhinovirus serotypes. Using this method, the ability to isolate serotypic subpopulations from a mixture was enhanced at least 7000-fold. This procedure allows the rapid isolation of variants which differ from the parent virus by as little as 4-fold in a serum neutralization test. Hence, viral preparations used to prepare reference grade reagents such as seed stocks and polyclonal and monoclonal antisera, can be tested for specificity prior to use.

Antigenic Variation↗
PubMed1989

Penetration of topically applied prednisolone sodium phosphate into human aqueous humour.

Gas Chromatography with Mass Spectrometry (GCMS) was utilised to determine the penetration of prednisolone sodium phosphate into the aqueous humour of human volunteers undergoing routine cataract extraction. Detectable levels of prednisolone were measured in the aqueous humour within 15 minutes. Peak concentrations occurred between 90 and 240 minutes, and the steroid could not be detected in samples taken 10 hours or more after topical administration.

Administration, Topical↗
PubMed1989

Analysis of biogenic amines in bovine retina by gas chromatography-negative ion chemical ionisation mass spectrometry.

Biogenic amines in bovine retina have been identified and quantified by an extraction-derivatisation procedure involving their reaction with 3,5-di(trifluoromethyl)benzoyl chloride (DTFMBCl) in the aqueous phase followed by extraction into an organic solvent, hydrolysis of phenolic esters, and conversion of free hydroxyl groups to trimethylsilyl ethers. Subsequent analysis of these DTFMB-trimethylsilyl derivatives by gas chromatography-negative ion chemical ionisation mass spectrometry revealed that the molecular ion carried most (greater than 60%) of the ion current, which made the method highly specific and gave a potential limit of detection below the picogram level. This method establishes unequivocally that the principal amines in bovine retina are p-tyramine, dopamine, and 5-hydroxytryptamine.

Animals↗
PubMed1988

An extraction-derivatization method suitable for the analysis of biogenic amines by gas chromatography negative ion mass spectrometry.

An extraction-derivatization method suitable for the analysis of subnanogram amounts of biogenic amines in aqueous solution has been developed. The most satisfactory procedure for the analysis of these compounds was reaction with 3,5-ditrifluorobenzoylchloride (DTFMBCl) in phosphate buffer at pH 7.2 followed by extraction of the resultant amide esters into ethyl acetate. This was followed by hydrolysis of the phenolic ester functionalities by shaking the organic layer with 10 M ammonium hydroxide. The phenolic and alcoholic hydroxyl groups were then reacted with bistrimethylsilylacetamide and the trimethylsilyl-DTFMB amides were then analysed by gas chromatography/mass spectrometry in the negative ion chemical ionization mode with methane as reagent gas. The limits of detection for these derivatives was less than 1 pg and the method was readily applicable to the extraction and analysis of 0.5 ng of a given biogenic amine.

Biogenic Amines↗
PubMed1988

The quantification of synthetic corticosteroids using isotope dilution gas chromatography negative chemical ionization mass spectrometry.

Prednisolone, dexamethasone and betamethasone were labelled with deuterium via a simple synthetic procedure and used as internal standards in the gas chromatographic/mass spectrometric analysis of the corresponding undeuterated compounds. The mass spectrometer was used in the negative chemical ionization mode, which gave fragmentation of the methoxime trimethylsilyl ether derivatives favourable for their quantification. The method was applicable to the quantification of synthetic corticosteroids contained in human aqueous humour in the 0.1-10-ng range.

Absorption↗