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Biomedical subjects

R Mitchell

Publications and source records attributed to R Mitchell.

At least 235 records · Page 13Linked to original sources
PubMed1990

The preservation of red cell antigens at low ionic strength.

Low-ionic-strength saline (LISS) techniques permit a safe and substantial reduction in incubation time and have therefore become the method of choice for antibody detection and compatibility testing in many transfusion laboratories. Consequently, the supply of reagent red cells (RBCs) in a low-ionic-strength preservative solution would remove the daily need for laboratories to wash and resuspend cells in LISS before use. However, the storage of fresh RBCs at low ionic strength in the presence of aminoglycoside antibiotics can cause a rapid loss of certain antigens, possibly as a result of the release of proteolytic enzymes from contaminating white cells. This article describes a low-ionic-strength solution that achieves preservation of antigens on liquid nitrogen-frozen-thawed RBCs for 21 days' storage at 4 degrees C.

Blood Preservation↗
PubMed1990

Distinct antinociceptive actions mediated by different opioid receptors in the region of lamina I and laminae III-V of the dorsal horn of the rat.

1. In view of the presence of mu, delta and kappa opioid receptors in the spinal dorsal horn and their apparent involvement in behavioural analgesia, the present experiments addressed the action of selective agonists ionophoresed in the vicinity of rat dorsal horn neurones which were located either in lamina I or in laminae III-V. 2. In laminae III-V, kappa agonists (U50488H and dynorphin A) caused a selective inhibition of the nociceptive responses of multireceptive cells, whilst mu and delta agonists [( D-Ala2, MePhe4, Gly-ol]enkephalin and [D-Pen2, D-Pen5]enkephalin respectively) failed to alter either the spontaneous activity or the response to noxious and innocuous cutaneous stimuli and to D,L-homocysteic acid or glutamate. Nocispecific neurones were encountered too rarely in laminae III-V to study their properties. 3. In lamina I, agonists had no effects on either nocispecific or multireceptive neurones. In contrast, the mu agonist [D-Ala2, MePhe4, Gly-ol]enkephalin consistently inhibited nociceptive responses of both multireceptive and nocispecific lamina I cells. The delta agonist [D-Pen2, D-Pen5]enkephalin consistently caused selective inhibition of the nociceptive responses of multireceptive cells but had a mixed profile of action on nocispecific cells. 4. These results suggest that mu, delta and kappa opioid receptors mediate different antinociceptive actions in both laminae III-V and lamina I. The study reveals a distinct physiological role for delta receptors in modulating nociceptive inputs to lamina I neurones. In contrast to mu and kappa receptor actions, delta receptors heterogeneously influence subpopulations of neurones.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1990

Ventricular ectopy during prolonged ambulatory electrocardiographic monitoring in elderly hypertensive subjects.

To examine whether ventricular ectopy in hypertensive older people is associated with age, the hypertensive process, or treatment, a 24-hour ambulatory electrocardiogram recording was obtained in 94 noninstitutionalized subjects aged 60-90 years with isolated hypertension and 136 noninstitutionalized normotensive subjects aged 60-82 years. A significantly higher prevalence of frequent ventricular ectopic beats (VEB greater than 100 per recording) was found in hypertensive and normotensive groups age greater than or equal to 70 years compared to age 60-69 years (44% vs 15%, P less than .01, and 28% vs 9%, P less than 01, respectively). Complex ventricular ectopy was found to be significantly increased only in the hypertensive group greater than or equal to 70 years compared to 60-69 years (53% vs 28%, P less than .05). No significant difference for any type of ventricular ectopy was found between treated and untreated hypertensive subjects. Analysis of variance of frequent ventricular ectopy showed a significant effect of age (P less than .001) but not of hypertension. Multivariate regression analysis with frequent ventricular ectopy as the dependent variable confirmed this relationship. For complex ventricular ectopy, analysis of variance showed a significant effect of hypertension (P less than .001) and age (P less than .05). Multivariate regression analysis confirmed that complex ventricular ectopy was significantly associated with hypertension (P less than .01) and age (P less than .05). In elderly subjects aging alone is associated with increased frequency of ventricular ectopy, whereas complex ventricular ectopy is more significantly related to the hypertensive process than to age.

Age Factors↗
PubMed1990

ACTH adrenal cell bioassay: improved sensitivity (12 ng/L) achieved by immunoextraction of ACTH from human plasma by a monoclonal antibody.

We have previously reported a bioassay for human plasma ACTH based upon trypsin dispersed guinea-pig adrenal cells which was sensitive to 100 ng/L ACTH in unextracted human plasma when measured against human pituitary ACTH (1-39) standard 74/555. We now present a bioassay of increased sensitivity (12 ng/L) which incorporates three major changes. The trypsin/trypsin inhibitor step in the cell dispersion protocol has been replaced with collagenase, donor calf serum (3%) has been incorporated into the standard curve and ACTH has been extracted from human plasma and dilutions of standard hormone by a sephacryl bound monoclonal antibody (2A3) directed towards the 25-39 sequence. The extracted standard curve has a detection limit of 6 ng/L and the cells can tolerate up to 50% plasma equivalent concentration. Thus, the improved assay has a detection limit of 12 ng/L ACTH in plasma. The assay can now measure bioactive plasma ACTH levels reliably in the normal range.

Adrenal Glands↗
PubMed1990

Computerised arthrotomography of primary anterior dislocation of the shoulder.

Computerised arthrotomography was performed on 33 patients four to six weeks after acute primary anterior dislocation of the shoulder. Seventeen patients were under, and 16 over 50 years of age. Damage to the anterior glenoidal labrum was seen in all the younger patients and in 75% of the older ones. A large redundant capsular pouch, seen in the older patients, was present in 35% of the younger ones, and a posterior humeral head defect was seen in 82% of the younger patients and only 50% of the older. Associated fractures were more common in the older patients, and a tear of the rotator cuff was demonstrated in 63% of the older patients and in none of the younger ones.

Adult↗
PubMed1990

The utilization of calcium soaps from animal fat by laying hens.

Ground wheat was employed as a carrier to evaluate the utilization by laying hens of animal fat, calcium soaps of fatty acids from animal fat (CS), and animal fat in the presence of 3.8% added calcium. Birds trained to consume their daily feed in two 1-h periods were fed ground wheat with 0, 3, 6, and 9% animal fat, CS, or 10% ground limestone and animal fat to provide 11 experimental diets. Animal fat and preformed CS were highly available to laying hens with total fatty acid availabilities of 100.2 +/- 1.2 (SE) and 99.2 +/- 3.6%, respectively, estimated by the regression of added fat on determined fat retentions. However, 3.8% calcium reduced animal-fat fatty acid availability to 86.3 +/- .7%. The true metabolizable energy of animal fat, as determined by regression from bomb-calorimetry data, was 9.63 +/- .58 kcal per g; a value of 9.36 kcal per g was obtained from fat-retention data [100.2% of the gross energy (GE) of 9.34 +/- .78 kcal per g]. With added limestone, the respective TME values were 9.36 +/- 1.30 kcal per g (regression) and 8.06 kcal per g (retention). The TME of the CS fatty acids was 7.20 +/- 1.05 kcal per g, estimated by regression; and the value calculated from CS fat retentions was 8.14 kcal per g, representing 99.2% of the GE (8.20 +/- .58 kcal per g). Discrepancies between calorimetric and fat-retention TME estimates represented animal-fat effects on wheat starch, fat, and amino-acid retentions.

Absorption↗
PubMed1989

Vascular endothelial growth factor: a new member of the platelet-derived growth factor gene family.

Using applications of the polymerase chain reaction (PCR) technique, cDNA clones have been isolated encoding bovine vascular endothelial growth factor (VEGF), a mitogen with specificity for vascular endothelial cells. Analysis of the clones indicates that VEGF can exist in two forms, probably due to alternative RNA splicing. The amino acid sequences predicted from the clones also show that VEGF shares homologies of about 21% and 24% respectively with the A and B chains of human platelet-derived growth factor (PDGF), and has complete conservation of the eight cysteine residues found in both mature PDGF chains. The homology is not reflected in function, however, since the cell types responsive to VEGF are distinct from those responsive to homo- and heterodimers of the PDGF chains.

Amino Acid Sequence↗
PubMed1989

The effect of some antiprostatic steroids upon cortisol production by guinea-pig adrenal cells stimulated by ACTH.

The antiprostatic steroids 6-methylene-4-pregnene-3,20-dione (6-MP) (I), 17-alpha-acetoxy-6, 16-dimethylene-4-pregnene-3,20-dione (II), and melengestrol acetate (MGA) (III) were incubated with guinea-pig adrenal cells, both alone and maximally stimulated with ACTH. Cortisol output was then measured by RIA. Increased cortisol-like secretion was obtained with 6-MP in the absence of ACTH. In the presence of ACTH, cortisol-like steroid secretion was the sum of that seen with ACTH and 6-MP alone. It follows that 6-MP stimulates in vitro a cortisol-like steroid cross reacting with the cortisol antibody by a mechanism that by-passes ACTH. Steroid (II) weakly inhibited cortisol output. MGA, in contrast, proved to be a strong inhibitor of cortisol output (ID50 of 2.3 mumol/l). Its site of action was established by adding it to adrenal cells incubated with precursor steroids on the cortisol pathway. Conversion of 3 beta-hydroxysteroids to cortisol was inhibited whereas conversion of 3-keto steroids was not affected. It follows that MGA inhibits 3 beta-hydroxysteroid dehydrogenase.

3-Hydroxysteroid Dehydrogenases↗
PubMed1989

The elimination of cross-infection in dental practice--a 5-year follow-up.

A survey in 1983 showed that 16% of general dental practitioners in the Lothian Region wore operating gloves when treating patients; 9% wore them continually and 7% only when performing dento-alveolar surgery. Twelve per cent replied that they would not consider wearing operating gloves and 72% stated that they might consider their use. A similar survey has now been completed 5 years later, involving practitioners in the Lothian and Borders regions. This shows that 163 (97%) of the 168 practitioners who replied now wear operating gloves; 51% restrict their use to the treatment of 'potentially infectious patients' and dento-alveolar surgery; 46% wear them continually. The main objections given to wearing gloves continually were loss of tactile sensation (67%) and cost (13%). The most difficult task to perform wearing gloves was root canal therapy (56%). The majority of practitioners (84%) believed that gloves reduced the dangers of cross-infection. The methods stated to be available for instrument sterilisation in 99.5% of practices were acceptable. This paper proposes that to eliminate cross-infection and protect the dental practitioner, operating gloves should be worn when treating all patients.

Attitude to Health↗
PubMed1989

Novel ligands for the affinity labelling of luteinizing hormone releasing hormone receptors.

A number of novel luteinizing hormone releasing hormone (LHRH) analogues incorporating biotin together with potential covalent attachment sites have been synthesized. Those based on the des-Gly10-[D-Lys6]-LHRH ethylamide peptide backbone resulted in the most useful characteristics of binding to the LHRH receptor in rat anterior pituitary gland membranes. Of these, des-Gly10-[biotinyl-aminoethylglycyl-D-Lys6]-LHRH ethylamide (XBAL) gave the best specific: non-specific binding ratio, with 44 +/- 6% (+/- S.E.M.) of total binding being specific with a Kd of 131 +/- 16 pM (+/- S.E.M., n = 4) as determined by Scatchard analysis. Two methods have been used to covalently crosslink these analogues with the LHRH receptor; photoaffinity labelling and the use of homobifunctional N-hydroxysuccinimide ester crosslinkers. The photoaffinity analogues gave poor specific: non-specific binding ratios. Of the chemical crosslinkers tested, ethylene glycolbis(succinimidylsuccinate) (EGS) was found to be the most efficient at covalently linking the 125I-XBAL bound to the LHRH receptor site. At an EGS concentration of 5 mM, 23 +/- 3% (+/- S.E.M.) of the specific binding of 125I-XBAL was covalently crosslinked.

Affinity Labels↗
PubMed1988

Heterogeneous effects of serotonin in the dorsal horn of rat: the involvement of 5-HT1 receptor subtypes.

The effect of ionophoretically applied serotonin (5-HT) was tested on cutaneous sensory responses of multireceptive dorsal horn neurones in the anaesthetized rat. Three types of 5-HT action were discerned: selective inhibition of nociceptive responses (10/18 cells), non-selective inhibition of responses to both noxious and innocuous stimuli as well as to excitatory amino acids (4/18 cells) and non-selective excitation of evoked responses (1/18 cells). A few cells (3/18) were unaffected by 5-HT. The use of agonists, shown to discriminate between subtypes of 5-HT1 receptor revealed that a 5-HT1A receptor agonist mimicked the non-selective effects of 5-HT, whereas a 5-HT1B receptor agonist mimicked the selective antinociceptive effects of 5-HT. A 5-HT2 receptor agonist, in contrast, was without effect. Both the selective and the non-selective effects were reversed by a 5-HT1 receptor antagonist, but not a 5-HT2 antagonist.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1988

The influence of opioid receptor subtypes on the processing of nociceptive inputs in the spinal dorsal horn of the cat.

Extracellular recordings were made of the cutaneous sensory responses of spinocervical tract (SCT) neurones in the lumbar dorsal horn of anaesthetised and paralysed cats. All of the neurones studied were multireceptive, showing excitatory responses to both innocuous and noxious (thermal and when tested, mechanical) stimuli applied to their cutaneous receptive fields on the ipsilateral hindlimb. The effects of iontophoretically applied opioids were studied on a regular cycle of responses to these cutaneous stimuli and also to D.L-homocysteic acid (DLH). In the first series of experiments, drugs were applied in the vicinity of the SCT neurones. The kappa-receptor agonists dynorphin A(1-13) and U50488H, but not dynorphin A(2-13), the mu-agonist DAGO, or the delta-agonist DADL, caused a selective reduction of the nociceptive responses of the neurones. The corresponding responses to innocuous stimuli or to DLH, and spontaneous activity were unaffected. In the second series of experiments, drugs were applied from a second electrode placed in the region of the substantia gelatinosa directly dorsal to the tip of the recording electrode. Under these conditions, the mu-receptor agonist DAGO, but not the kappa-agonist dynorphin A(1-13) or the delta-agonists DADL, DSLET or DLPEN, showed a selective antinociceptive effect. In both series, the antinociceptive effects of the opioids were readily reversed by iontophoretically applied naloxone. The effect of dynorphin A(1-13) applied close to SCT neurones, but not that of DAGO applied in the region of the substantia gelatinosa, was reversed by the alpha 2-adrenoceptor antagonist, idazoxan. The results indicate that both mu- and kappa-opioid receptors (at anatomically distinct sites) can participate in the selective antinociceptive influence that opioids can exert over somatosensory information ascending to supraspinal levels. The antagonism of kappa-receptor-mediated antinociception by idazoxan is consistent with an interaction of opioid and noradrenaline influences at the level of the dorsal horn.

Animals↗