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Biomedical subjects

D Perrett

Publications and source records attributed to D Perrett.

At least 91 records · Page 5Linked to original sources
PubMed1988

Nucleosides and bases in synovial fluid from patients with rheumatoid arthritis and osteoarthritis.

1. Nucleosides and bases in physiological fluids result from metabolism of nucleic acids and nucleotides and from dietary sources. As nucleotide catabolism increases during tissue injury, nucleosides and bases could serve as useful biochemical markers in arthritis. 2. We have quantified nucleosides and bases in synovial fluid and plasma by high-performance liquid chromatography in order to examine whether nucleotide metabolism is increased in patients with rheumatoid arthritis and osteoarthritis. 3. At least ten u.v.-absorbing compounds were detected in plasma and synovial fluid; only urate, creatinine, hypoxanthine and uridine were present in identifiable and quantifiable amounts. 4. In synovial fluid from patients with rheumatoid arthritis the concentration of hypoxanthine was increased and that of urate decreased compared with osteoarthritis. 5. These data suggest that there is an increase in purine metabolism in the rheumatoid arthritis joint and that hypoxanthine is a potential marker of synovitis.

Adult↗
PubMed1988

Modulation of the actions of tyrosine by alpha 2-adrenoceptor blockade.

1. Eight normal subjects were given, in double-blind, random order L-tyrosine 50, 250 and 500 mg kg-1 and placebo orally. Plasma tyrosine concentrations rose in a dose-dependent manner, without affecting the concentrations of the other large neutral amino acids. Tyrosine stimulated the secretion of prolactin and thyrotrophin (TSH) but had no effect on the plasma concentrations of adrenocorticotrophic hormone (ACTH), cortisol, growth hormone or the gonadotrophins. 2. The lack of a stimulant effect of tyrosine on ACTH secretion was presumed to be due to activation of one of the negative feedback mechanisms that control the rate of synthesis and release of the catecholamines, and this hypothesis was tested by examining the effects of the alpha 2-adrenoceptor antagonist idazoxan on the actions of tyrosine. 3. Seven normal males were given on 6 separate occasions tyrosine 250 and 500 mg kg-1 and placebo orally following pretreatment with saline and idazoxan (0.1 mg kg-1 i.v.). Following pretreatment with idazoxan, tyrosine stimulated the secretion of ACTH and noradrenaline in a dose-dependent manner, although neither tyrosine nor idazoxan on their own had any effect on the secretion of either substance. 4. The lack of effect of tyrosine when given on its own appears to be due, to partly, to activation of alpha 2-adrenoceptors, which inhibit the release of noradrenaline. Idazoxan caused a small increase in systolic blood pressure, both when given on its own and in combination with tyrosine. Neither tyrosine nor idazoxan had any significant effect on the state of behavioural arousal, as measured by visual analogue scales, or on the secretion of growth hormone or the gonadotrophins.

Adrenergic alpha-Antagonists↗
PubMed1988

Failure of oral thiomalate to act as an alternative to intramuscular gold in rheumatoid arthritis.

Ten patients with active rheumatoid arthritis (RA) were entered into a pilot study to evaluate the effectiveness of thiomalic acid as a disease modifying agent and to assess its toxicity. Oral thiomalic acid (100 mg) was given daily for up to six months. Changes in disease activity were recorded monthly and all side effects noted. No patient recorded any improvement in subjective well being, pain score, or duration of early morning stiffness. No significant change occurred in articular index or haemoglobin (Hb); the erythrocyte sedimentation rate (ESR) showed a tendency to increase. Only three patients completed six months' treatment; six withdrew because of toxic reactions (three with rashes and three with severe gastrointestinal upset) and one because of lack of effect. Thiomalic acid alone appears to have no significant antirheumatic activity and is associated with an unacceptably high incidence of adverse reactions.

Absorption↗
PubMed1987

Determination of adenosine ribo- and deoxyribonucleotides as their 1-N6-etheno derivatives by reversed-phase ion-pair high-performance liquid chromatography.

The chromatographic resolution of fluorescent 1-N6-etheno derivatives of adenine and adenosine ribo- and deoxyribonucleotides on reversed-phase columns has been optimised by a systematic study of the effect of ion-pair concentration, pH, eluent molarity and methanol concentration. Using tetrabutylammonium hydrogen sulphate as the ion-pair separation of up to eight derivatives could be achieved in ca. 10 min. Conditions of derivatisation with chloroacetaldehyde have been investigated in order to reduce hydrolysis of the nucleotides.

Adenine Nucleotides↗
PubMed1987

The determination of cysteamine in physiological fluids by HPLC with electrochemical detection.

Cysteamine, an amino thiol, was separated by rapid isocratic cation exchange chromatography and detected by electrochemical oxidation at a platinum electrode maintained at +0.45 V relative to an Ag/AgCl reference electrode. Eluent pH and electrode working potentials were optimized and the effects of alternative buffers and organic modifiers have been examined. On column sensitivity for cysteamine was 1.5 pmol at a signal-to-noise ratio of 5. Although the specificity was good, plasma samples required maximal sensitivity whereas urine samples required greater selectivity, which was achieved by use of lower working potentials. Cysteamine concentrations were determined in serial samples of plasma and urine from volunteers who had received a single oral dose of 200 mg of the drug. Cysteamine was rapidly oxidized in vivo, and detection required prior reduction with dithiothreitol before analysis.

Chromatography, High Pressure Liquid↗
PubMed1986

An in-situ isolated rat adrenal perfusion system for study of neurally mediated catecholamine secretion: effects of morphine, a Met-enkephalin analogue, and naloxone on catecholamine secretion.

An in-situ isolated rat adrenal perfusion technique has been devised to study the opioid control of neurally mediated adrenomedullary catecholamine release. Adrenomedullary catecholamine secretion was induced by electrical stimulation of the cut end of the left descending thoracic sympathetic chain on platinum electrodes. The half-maximal stimulatory potential (ED50) of the system was 8 V, 20 Hz, with 300 microseconds pulse width. Basal release of catecholamine from the adrenal was constant using a perfusion flow rate of 100-300 microliter/min, but increased significantly with increasing perfusion temperature over the range 36-38 degrees C. Following repetitive 30-s stimulation of the left thoracic sympathetic chain, and 3-min fraction collections, the total amount of catecholamine released per fraction remained within 80-100% of the maximum release for up to eight consecutive stimuli. The release of catecholamines was completely blocked by hexamethonium (0.1 mmol/l), but recovered to pre-blockade values within two further stimuli. Using the ED50 and the first three stimuli as control, the effects of morphine (10 nmol/l-l mmol/l), D-Ala2-MePhe4-Met-enkephalin-(O5)-ol (DAMME; 10 nmol/l-0.1 mmol/l) and naloxone (10 nmol/l-10 mumol/l) on the response to the next three stimuli were compared. Morphine, DAMME or naloxone did not significantly alter the amount of catecholamine released by this form of stimulation. Therefore in the rat, under the conditions used, there is no evidence for mu (mu) or delta (delta) opiate modulation of neurally mediated catecholamine release from the rat adrenal medulla.

Adrenal Glands↗
PubMed1986

The use of D-penicillamine in patients with rheumatoid arthritis undergoing hemodialysis.

D-penicillamine and its major metabolites cysteine-penicillamine disulphide (CP) and penicillamine disulphide (P2) concentrations were measured in plasma from a hemodialysis patient with rheumatoid arthritis. CP and P2 alone were measured in plasma and a plasma ultrafiltrate from a second patient. On penicillamine 250 mg thrice weekly taken after dialysis pre-dialysis penicillamine concentrations were in the range 5.9-9.9 mumol/l. CP and P2 concentrations remained stable (range 139-197 mumol/l and 10-20 mumol/l) over 5 weeks and were of the same order as previously found in patients with normal renal function on higher doses of the drug. On penicillamine 250 mg daily concentrations of metabolites CP and P2 reach 193 mumol/l and 59.2 mumol/l after 2 and 3 weeks respectively. Concentration of metabolites fell by about half and of penicillamine by about a third after dialysis. Concentration of metabolites in ultrafiltrate were on average 75% lower than in plasma. Penicillamine 250 mg thrice weekly given after dialysis appears to be an appropriate dose for hemodialysis patients with rheumatoid arthritis.

Arthritis, Rheumatoid↗
PubMed1985

Interference of labetalol metabolites in the determination of plasma catecholamines by HPLC with electrochemical detection.

The alpha and beta adrenoceptor blocking drug labetalol is a potent antihypertensive agent in widespread clinical use. Its interference in the classical chemical estimations of urinary catecholamines and their metabolites has been the subject of several reports. Factitiously raised values have been noted in both the fluorimetric catecholamine assay, and the standard spectrophotometric procedure for total (free and conjugated) metadrenalines. To avoid such drug interference, modification of these methods is required in the estimation of catecholamines and their o-methylated metabolites. Alternatively, VMA estimations or plasma/urinary catecholamine measurements by radioenzymatic assay may be used in patients on labetalol. Although high performance liquid chromatography coupled with electrochemical detection (HPLC-ECD) methods for estimation of plasma catecholamines are now in widespread use, the interference of labetalol in this method has not been reported. We now report that significant direct interference of labetalol in the HPLC-ECD assay does indeed occur, and can yield spuriously raised adrenaline levels.

Aluminum Oxide↗
PubMed1985

Methodological considerations in the determination of plasma catecholamines by high-performance liquid chromatography with electrochemical detection.

We report on a systematic investigation into some frequently encountered problems in the estimation of catecholamines in plasma and biological fluids using high-performance liquid chromatography with electrochemical detection. The kinetics of adsorption and desorption of catecholamines from plasma on to alumina has been studied using laboratory-prepared and some commercial aluminas with various acids. Chromatographic conditions yielding optimal resolution and sensitivity have been characterised. Some possible interfering peaks have been identified. The stability of catecholamines in plasma has been studied.

Adolescent↗
PubMed1984

Post-ischaemic synchronous purine nucleotide oscillations in perfused rat heart.

Langendorff perfused rat hearts show synchronous, statistically significant, systematic variations in ATP and ADP. Here we show that AMP and IMP also vary in register with ATP and ADP and we suggest that the synchronizing trigger for these oscillations may be ischaemia. Oscillations in the ATP/ADP ratio were found to be significantly correlated with creatine phosphate content but by contrast these quantities vary quite differently from the GTP/GDP ratio. Cyclic GMP oscillations showed a significant negative correlation with variations in ADP. Epinephrine raised mean cyclic AMP content and stabilized cyclic GMP oscillations, but had little other effect on the purine nucleotide variations.

Adenosine Diphosphate↗
PubMed1984

Structural requirements for activity of certain 'specific' antirheumatic drugs: more than a simple thiol group?

The relationship between chemical structure and the clinical activity and toxicity of several second-line antirheumatic drugs is examined. The presence of a thiol group in many of these agents has previously been noted, but most of the compounds additionally either possess, or form metabolites containing, the ethanethiol backbone or a similar ring structure. This applies not only to penicillamine and disodium aurothiomalate but also to thiola , 5- thiopyridoxine , levamisole and captopril. The presence of free circulating thiols has recently been shown for several of these compounds including free thiomalate in the case of disodium aurothiomalate, which on a molar basis is the most potent agent of all. Further study of thiomalate and related compounds in vitro and in vivo may clarify the pathogenesis of rheumatoid arthritis as well as allowing the development of more effective and less toxic second-line agents.

Anti-Inflammatory Agents↗
PubMed1984

Free thiomalate in plasma and urine of patients receiving sodium aurothiomalate.

Free thiomalate is measureable in the plasma and urine of patients with rheumatoid arthritis receiving sodium aurothiomalate (Myocrisin). Plasma concentrations and urinary excretion of free thiomalate were measured in 8 patients by high-performance liquid chromatography and electrochemical detection. After an initial intramuscular dose of 20 mg sodium aurothiomalate, free thiomalate was detected in plasma within 15 min, peak levels of up to 600 nmol/l occurring at 30 min. Plasma levels declined rapidly thereafter. During the first 24 h between 2 and 16% of the injected dose of aurothiomalate was recovered in the urine as free thiomalate, maximum excretion occurring during the first hour.

Adult↗
PubMed1984

Free thiomalate levels in patients with rheumatoid arthritis treated with disodium aurothiomalate: relationship to clinical outcome of therapy.

Sixteen patients with seropositive rheumatoid arthritis were treated with 20 mg disodium aurothiomalate (Myocrisin) weekly for six months. Disease activity was assessed before and after treatment. Plasma profiles and urinary excretion of free thiomalate were measured in all patients after the initial injection and again at six months in the 12 patients remaining on therapy. No difference was found in plasma levels or urinary excretion of free thiomalate between patients who responded to treatment or who developed toxic reactions and those who did not.

Adult↗