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Biomedical subjects

C M Brown

Publications and source records attributed to C M Brown.

At least 145 records · Page 8Linked to original sources
PubMed1991

Structure-affinity relationships of 12-sulfonyl derivatives of 5,8,8a,9,10,11,12,12a,13,13a-decahydro-6H-isoquino[2,1-g][1 ,6] naphthyridines at alpha-adrenoceptors.

Analogues of the potent alpha 2-adrenoceptor antagonist (8aR,12aS,13aS)-5,8,8a,9,10,11,12,12a,13,13a- decahydro-3-methoxy-12-(methylsulfonyl)- 6H-isoquino[2,1-g][1,6]naphthyridine (1b) were prepared and evaluated for alpha 1- and alpha 2-adrenoceptor affinity. Affinity for alpha 2-adrenoceptors was assessed by displacement of [3H]yohimbine from rat cerebral cortical membranes and although 1b and close structural analogues demonstrated high affinity, none were selective for the alpha 2A or alpha 2B subtypes reputedly present in this tissue. All of the high affinity alpha 2-adrenoceptor ligands were, however, selective with respect to [3H]prazosin (alpha 1) binding. Affinity for [3H]yohimbine-labeled alpha 2-adrenoceptors was found to be highly dependent on the stereochemistry of the tetracyclic system. The 8a beta,12a alpha,13a alpha diastereomer of 1 (56) had moderate affinity for alpha 2-adrenoceptors while the 8a beta,12a beta,13a alpha diastereomer (55) had very low affinity. The affinity and selectivity of these agents for alpha 2-adrenoceptors was found to correspond to that observed for several isomeric yohimbine analogues which have similar relative and absolute stereochemistries. Deviation from the structure of 1 by opening the B ring, changing the position of the sulfonamide nitrogen, or changing the attachment of the D ring led to a dramatic decrease in alpha 2-adrenoceptor affinity. High binding affinity was found to correlate with functional antagonism in the guinea pig ileum. The reversal of clonidine-induced mydriasis in the rat was used to assess bioavailability and indicated that 1b was a potent alpha 2-adrenoceptor antagonist in vivo.

Adrenergic alpha-Antagonists↗
PubMed1991

The guinea-pig ileum preparation as a model for 5-HT1A receptors: anomalous effects with RS-30199-193.

1. Agents that have high and selective affinity for the 5-HT1A site such as 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and N,N-dipropyl-5-carboxamidotryptamine (DP5CT) inhibited the responses to field stimulation in guinea-pig ileum preparations; the inhibitory effects were antagonized by methiothepin and spiperone, consistent with effects at the 5-HT1A site. 2. The inhibitory effects of DP5CT were pronounced in Tyrode solution containing low Ca2+ (0.9 mM), but were much less apparent in Tyrode solution containing 1.8 or 5.4 mM Ca2+. 3. Responses to DP5CT were abolished by pretreatment with phorbol dibutyrate (3 microM), whereas the responses to UK14304 were only slightly inhibited. 4. Buspirone and ipsapirone (1 microM) inhibited the responses to field stimulation, and the effects were resistant to idazoxan, but inhibited by 8-OH-DPAT or spiperone. 5. RS-30199-193 (5-chloro-2-methyl-1,2,3,4,8,9,10,10a-octahydronaphth-[1,8-cd]- aze pine hydrochloride) an azepine with high affinity for the 5-HT1A site in rat cerebral cortex in binding experiments, augmented contractions, but did not antagonize the responses to DP5CT or to 8-OH-DPAT. 6. The hybrid compound of RS-30199-193 with buspirone, RS-64459-193 (5-chloro-2-[4-(8-azaspiro[4,5]decane-7,9-dione)-but-1-yl]- 1,2,3,4,8,9,10,10a-octahydronaphth[1,8-cd]-3-azepine hydrochloride) maintained high affinity for the 5-HT1A binding site in rat brain and both inhibited the response to field stimulation and antagonized the responses to 8-OH-DPAT and DP5CT. Thus the buspirone side chain when added to RS-30199-193 appears either to induce affinity for a distinct subset of receptors in the guinea-pig ileum or is required for functional effectiveness at the 5-HTlA receptor.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1991

Are there more than two types of alpha-adrenoceptors involved in physiological responses?

The application of the four main techniques available for examining the properties of alpha-adrenoceptors, gene coding, radioligand, biochemical and functional methods, has reinforced the earlier subclassification (alpha 1- and alpha 2-subtypes). These different techniques have not yet yielded subclassifications which entirely align when the subtypes have been examined in detail, although a prime reason for this is that the different techniques have not yet all been applied to the same receptors. There is evidence available on each level to indicate that there are further subtypes within the alpha 1- and alpha 2-adrenoceptors as originally defined pharmacologically, with the possible exception of functional evidence at cellular and tissue level for subtypes of alpha 2. The present extension of the subclasses to three each (A,B,C) for alpha 1 and alpha 2 does not withstand cross-examination on every level and seems unlikely to withstand further probing. It remains true that the set of subtypes of alpha-adrenoceptor which can be activated or blocked by drugs in functioning intact tissue preparations and which are shown in Fig. 4 has not been added to by knowledge derived from ligand binding or molecular biology. These techniques have bolstered confidence in the existing functioning categories and have enabled acceleration of drug screening programmes to find new, potent, highly selective antagonists for the known receptors. Rather than taking the categorization of receptors away from the recognition site to the larger molecule, they have reinforced its supremacy. The advantages being gained from the molecular biology of receptors lie in understanding cell signalling and, on the wider genetic scale, on the place of the receptors, among other elements of the cell, in regulation and function within the organism. From the physiologist's point of view, classical pharmacology can still be relied on as the basis for understanding the specificity of drugs which activate or block plasmalemmal receptors and to keep the numbers of these receptors within reason, while molecular biology may increasingly provide the tools to study the subsequent physiological events. A few years ago, one of us commented (in jest!) that the availability of so many different techniques for examining the properties of alpha-adrenoceptors may eventually provide the ultimate answer that there are forty-two subtypes, but that along the way, the original reason for requiring classification might become lost (McGrath, 1983 b).(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenergic alpha-Agonists↗
PubMed1991

A microbiological comparison of young adults based on relative amounts of subgingival calculus.

This study compared the relative amounts of Actinobacillus actinomycetemcomitans (Aa), Eikenella corrodens (Ec), and black-pigmented anaerobic rods, and the proportions of coccoid forms, nonmotile rods, motile rods, spirochetes, and total motile organisms in subgingival plaque samples from 2 groups of young adults with generalized moderate to severe periodontitis. Two groups of 12 untreated patients were selected based on the relative amounts of subgingival calculus detected. Subgingival plaque samples (2 sites/patient) were taken with a sterile curet, dispersed, and plated under anaerobic conditions on ETSA, ETSA-kanamycin, ETSA-clindamycin, and TSBV agar. Appropriate biochemical tests were performed to confirm suspected microorganisms. Phase-contrast microscopy also was used to count the relative numbers of coccoid forms, nonmotile rods, motile rods, and spirochetes in each of the samples. Patients with no clinically detectable subgingival calculus harbored significantly greater proportions (%) of coccoid forms and Aa and greater amounts (CFU/mg) of Aa than did patients with obvious amounts of subgingival calculus. Subjects with clearly detectable subgingival calculus possessed greater proportions of motile rods, total motile organisms, and black-pigmented anaerobic rods than did subjects with little or no subgingival calculus. Young adult patients with generalized moderate to severe disease and little or no detectable subgingival calculus may possess a subgingival microbiota with relatively higher numbers of Aa and coccoid forms, and a lower percentage of BPB, motile rods, and total motile organisms as compared to similar patients with greater amounts of subgingival calculus.

Adult↗
PubMed1991

The DNA sequence of the human cytomegalovirus genome.

In the first part of this article we review what has been learnt from the analysis of the sequence of HCMV. A summary of this information is presented in the form of an updated map of the viral genome. HCMV is representative of a major lineage of herpesviruses distinct from previously sequenced members of this viral family and demonstrates striking differences in genetic content and organization. The virus encodes approximately 200 genes, including nine gene families, a large number of glycoprotein genes, and homologues of the human HLA class I and G protein-coupled receptor genes. The HCMV sequence thus provides a sound basis for future molecular studies of this highly complex eukaryotic virus. The second part discusses the practical rate of DNA sequencing as deduced from this and other studies. The 229 kilobase pair DNA genome of human cytomegalovirus (HCMV) strain AD169 is the largest contiguous sequence determined to date, and as such provides a realistic benchmark for assessing the practical rate of DNA sequencing as opposed to theoretical calculations which are usually much greater. The sequence was determined manually and we assess the impact of new developments in DNA sequencing.

Base Sequence↗
PubMed1991

A clinical evaluation of the Sulcabrush.

The purpose of this study was to compare the effectiveness of a unituft brush in combination with a conventional brush for plaque removal and maintenance of gingival health. Thirty patients presenting for routine dental care were examined and scored for plaque deposits and gingival inflammation. All subjects received a dental prophylaxis consisting of removal of all supragingival and subgingival deposits and polishing of the clinical crowns. Subjects were subsequently evaluated at 1 week, 6 weeks and 12 weeks. The addition of a unituft brush to the patient's regimen of oral hygiene procedures resulted in significant reductions at 12 weeks in both plaque scores (p less than .05) and gingival inflammation (p less than .01) when compared to the use of the conventional brush alone.

Adult↗
PubMed1990

Sequence analysis suggests that tetra-nucleotides signal the termination of protein synthesis in eukaryotes.

An increasing number of cases where tri-nucleotide stop codons do not signal the termination of protein synthesis are being reported. In order to identify what constitutes an efficient stop signal, we analysed the region around natural stop codons in genes from a wide variety of eukaryotic species and gene families. Certain stop codons and nucleotides following stop codons are over-represented, and this pattern is accentuated in highly expressed genes. For example, the preferred signal for Saccharomyces cerevisiae and Drosophila melanogaster highly expressed genes is UAAG, and generally the signals UAA(A/G) and UGA(A/G) are preferred in eukaryotes. The GC% of the organism or DNA region can affect whether there is A or G in the second or fourth positions. We suggest therefore, that the stop codon and the nucleotide following it comprise a tetra-nucleotide stop signal. A model is proposed in which the polypeptide chain release factor, a protein, recognises this sequence, but will tolerate some substitution, particularly A to G in the second or third positions.

Animals↗
PubMed1990

The signal for the termination of protein synthesis in procaryotes.

The sequences around the stop codons of 862 Escherichia coli genes have been analysed to identify any additional features which contribute to the signal for the termination of protein synthesis. Highly significant deviations from the expected nucleotide distribution were observed, both before and after the stop codon. Immediately prior to UAA stop codons in E. coli there is a preference for codons of the form NAR (any base, adenine, purine), and in particular those that code for glutamine or the basic amino acids. In contrast, codons for threonine or branched nonpolar amino acids were under-represented. Uridine was over-represented in the nucleotide position immediately following all three stop codons, whereas adenine and cytosine were under-represented. This pattern is accentuated in highly expressed genes, but is not as marked in either lowly expressed genes or those that terminate in UAG, the codon specifically recognised by polypeptide chain release factor-1. These observations suggest that for the efficient termination of protein synthesis in E. coli, the 'stop signal' may be a tetranucleotide, rather than simply a tri-nucleotide codon, and that polypeptide chain release factor-2 recognises this extended signal. The sequence following stop codons was analysed in genes from several other procaryotes and bacteriophages. Salmonella typhimurium, Bacillus subtilis, bacteriophages and the methanogenic archaebacteria showed a similar bias to E. coli.

Amino Acids↗
PubMed1990

Experience of MOET with Welsh Black cattle in a group breeding scheme.

The embryo production records of 27 Welsh Black cows in a multiple ovulation and embryo transfer (MOET) program were examined. Significant monthly variations in the number of viable embryos recovered (P=0.07) and in embryo viability (P=0.002) were detected, although ovarian responses did not vary. Embryo recovery was not affected by the type of catheter used or by the side of the uterus flushed.

Journal Article↗
PubMed1990

Destruction of hearing aid by lightning strike.

A 20-year-old woman was struck by lightning while seeking shelter under a tree. The discharge entered at the site of the victim's behind-the-ear type hearing aid, destroying it. She suffered cardiorespiratory arrest, burns, left ventricular failure, and myoglobinuria, yet recovered fully. It is widely known that carrying a metallic object such as an umbrella or golf club above one's head increases the risk of being struck. However, few people know that small metallic objects worn on the head are similarly dangerous. Persons caught outside in a lightning storm might decrease the probability of being struck by removing all metallic objects from their head.

Adult↗
PubMed1990

Affinity of 2-(tetrahydroisoquinolin-2-ylmethyl)- and 2-(isoindolin-2-ylmethyl)imidazolines for alpha-adrenoceptors. Differential affinity of imidazolines for the [3H]idazoxan-labeled alpha 2-adrenoceptor vs the [3H]yohimbine-labeled site.

A series of 2-(tetrahydroisoquinolin-2-ylmethyl)- and 2-(isoindolin-2-ylmethyl)imidazolines were prepared and tested for alpha 1- and alpha 2-adrenoceptor affinity with radioligand binding. Several compounds, 5-fluoro-(5h), 5-chloro-(5j), 5,8-dimethoxy- (5r), and 5,8-dimethoxy- (5r),1-methyl- (5s) 2-(tetrahydroisoquinolin-2- ylmethyl)imidazoline, were found to be selective alpha 2-adrenoceptor ligands on the basis of displacement of [3H]yohimbine from rat cerebral cortical membranes. One compound, 2-[(8-chloro tetrahydroisoquinolin-2-yl)methyl]imidazoline (5m), showed a 36-fold difference in affinity for the [3H]idazoxan-labeled alpha 2-adrenoceptor relative to the [3H]yohimbine-labeled site, which may be evidence for alpha 2-adrenoceptor subtypes.

Animals↗
PubMed1990

1,9-Alkano-bridged 2,3,4,5-tetrahydro-1H-3-benzazepines with affinity for the alpha 2-adrenoceptor and the 5-HT1A receptor.

A number of 1,9-alkano-bridged 2,3,4,5-tetrahydro-1H-3-benzazepines were prepared and evaluated for 5-HT1A receptor and alpha 2-adrenoceptor affinity by using radioligand receptor binding techniques. Several compounds displayed 5-HT1A receptor affinity comparable to, or greater than, the known 5-HT1A ligand buspirone. The highest affinity 5-HT1A receptor ligands were N-alkyl-, N-allyl-5-chloro-, and 5-methoxy-1,2,3,4,8,9,10,10a-octahydronaphth[1,8-cd]azapines (4c, 4m, 4n), which had pKi values of 7.9-8.1. The S enantiomer of 4c had a higher affinity for the 5-HT1A receptor than the corresponding R isomer (pKi of 8.2 for (S)-4c vs 7.7 for (R)-4c). These compounds had a relatively low affinity for the alpha 2-adrenoceptor (pKi of 7 or less). On the other hand, the closely related 5-chloro-2-methyl-2,3,4,8,9,9a-hexahydro-1H-indeno[1,7-cd]azepine (3b) had high affinity for both the alpha 2-adrenoceptor (pKi = 8.1) and 5-HT1A receptor (pKi = 7.6). These results indicate that the two receptors may share common recognition sites.

Animals↗
PubMed1990

Analysis of immunoglobulins secreted by hybridomas derived from rheumatoid synovia.

Twenty-six IgG-secreting and eight IgM-secreting hybridomas were derived from the synovia of two patients with rheumatoid arthritis (RA). Hybridomas were obtained by fusing a heteromyeloma cell line, SPAZ-4 with synovial mononuclear cells that were not deliberately stimulated in vitro. Over 96% of the IgG-secreting hybridomas produced antibodies which belonged to the IgG1 subclass and showed lambda light chain predominance; the latter was not seen in IgM antibodies, where kappa light chains dominated by 3:1. All IgG antibodies were cationic. Synovial B cells were not exposed to extrinsic stimuli prior to fusion, therefore these results reflect the state of B cell activation and differentiation in vivo. Our results indicate that IgG-secreting B cells in the RA joint are under a selective influence which is, as yet, unidentified. One out of eight IgM-secreting and two out of 26 IgG-secreting hybridomas produced rheumatoid factors (RF). The IgM-RF specificity for IgG heavy chain subclasses was determined and showed that the monoclonal bound to IgG1, IgG2 and IgG4 but not IgG3 with exception of IgG3 Goe of the G3m (st) allotype, a profile typical of specificity for the Ga epitope. This monoclonal also distinguished a determinant in the Fc region of human IgG which was not present in rabbit IgG. The overall frequency of RF-secreting hybridomas we observed indicates that B cells committed to RF production in the synovium of a seropositive and a seronegative RA patient is below 10%.

Adult↗
PubMed1990

Heterogeneity of alpha 2-adrenoceptors in rat cortex but not human platelets can be defined by 8-OH-DPAT, RU 24969 and methysergide.

1. Saturation experiments indicated that [3H]-yohimbine binding was specific, saturable and labelled a single population of sites in rat cerebral cortex (Kd 5.3 +/- 0.9 nM, Bmax 121 +/- 10 fmol mg-1 protein) and human platelets (Kd 0.7 +/- 0.1 nM, Bmax 152 +/- 10 fmol mg-1 protein). 2. The alpha 2-adrenoceptor antagonists, yohimbine, rauwolscine, WY 26703, idazoxan and BDF 6143 displaced [3H]-yohimbine binding to each tissue in a simple manner, with high affinity and Hill slopes close to unity. 3. The alpha 1-adrenoceptor agonist, oxymetazoline and the antagonist prazosin inhibited the binding of [3H]-yohimbine to rat in a complex manner consistent with an interaction at more than one site. However, indoramin and WB 4101 only appeared to interact with one site. In contrast, in human platelets, all antagonists gave rise to monophasic displacement curves with Hill slopes close to unity suggesting a single site of interaction. 4. The 5-hydroxytryptamine (5-HT) receptor ligands, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), RU 24969, and methysergide inhibited the binding of [3H]-yohimbine to rat cortex with high and low affinity, consistent with an interaction with two populations of binding sites. However, inhibition of [3H]-yohimbine binding to human platelets suggested a single site of interaction. The low affinity of 5-HT, 5-carboxyamidotryptamine (5-CT) and dipropyl-5-CT indicated that [3H]-yohimbine was not labelling a 5-HT1-like site in rat cortex. 5. The ability of 8-OH-DPAT, RU 24969 and methysergide in addition to prazosin and oxymetazoline to differentiate [3H]-yohimbine binding provides additional pharmacological evidence for heterogeneity within rat cortical alpha 2-adrenoceptors. However, if the two sites in rat cortex that are differentiated by the 5-HT ligands represent (alpha 2A- and alpha 2B-adrenoceptor subtypes as defined by prazosin and oxymetazoline, then they do not correspond to the population of sites in human platelets. As receptor classification should be linked to affinity of drugs rather than tissue distribution, the current classification of alpha 2-adrenoceptor subtypes does not appear to be satisfactory.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1990

Alpha 2-adrenoceptor subtypes and imidazoline-like binding sites in the rat brain.

1. The binding of [3H]-yohimbine and [3H]-idazoxan to rat cortex and hippocampus is rapid, reversible and of high affinity. Saturation data indicate that a single population of binding sites exist for [3H]-yohimbine in the cortex (Bmax 121 +/- 10 fmol mg-1, protein; Kd 5.2 +/- 0.9 nM) and hippocampus (Bmax 72 +/- 6 fmol mg-1 protein; Kd 5.8 +/- 0.7 nM). [3H]-idazoxan labels one site in the cortex (Bmax 87 +/- 8 fmol mg-1 protein; Kd 4.1 +/- 0.9 nM) and hippocampus (Bmax 30 +/- 6 fmol mg-1 protein; Kd 3.5 +/- 0.5 nM), when 3 microM phentolamine is used to define non-specific binding. A second distinct [3H]-idazoxan binding site (Bmax 110 +/- 21 fmol mg-1 protein; Kd 3.6 +/- 0.07 nM) is identified in rat cortex if 0.3 microM cirazoline is used to define non-specific binding and 3 microM yohimbine is included to prevent binding to alpha 2-adrenoceptors. 2. Displacement studies indicate that the alpha 1-adrenoceptor antagonist prazosin and the 5-HT1 ligands 8-OH-DPAT, RU 24969 and methysergide differentiate [3H]-yohimbine binding into two components; a high and low affinity site. In contrast the displacement of [3H]-idazoxan by each ligand was monophasic. 3. The affinities of 8-OH-DPAT, RU 24969 and methysergide determined against [3H]-idazoxan binding to the cortex and hippocampus correlate significantly with the binding site displaying low affinity for prazosin and previously designated alpha 2A. In contrast, a poor correlation exists for the high affinity site for prazosin designated alpha 2B. 4. [3H]-idazoxan, in the presence of 3 microM yohimbine, labels a site that displays high affinity towards cirazoline, naphazoline and guanabenz, but low affinity towards clonidine, p-aminoclonidine, adrenaline, noradrenaline and the alpha 2-adrenoceptor antagonists yohimbine, rauwolscine, WY 26703 and BDF 6143. 5. The results of this study indicate that [3H]-yohimbine labels two sites; the alpha 2A- and alpha 2B-adrenoceptors whereas [3H]-idazoxan labels an alpha 2-adrenoceptor with a profile consistent with the alpha 2A-adrenoceptor subtype. In addition, [3H]-idazoxan labels an imidazoline binding site in the rat cortex that is pharmacologically distinct from alpha 2-adrenoceptors. The low affinity of clonidine and p-aminoclonidine indicates that the imidazoline-like binding site in rat cortex is different from the site labelled by [3H]-clonidine and [3H]-p-aminoclonidine in human, rat and bovine brain stem, providing evidence of potential heterogeneity within this class of binding sites.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1990

A tracheoscopic technique for obtaining uncontaminated lower airway secretions for bacterial culture in the horse.

Transtracheal aspirate (TTA) aerobic microbiology culture results from 30 ponies were compared to protected catheter brush (PCB) culture results obtained from the same ponies. The PCB procedure resulted in significantly fewer (P less than 0.05) isolates than those obtained by the TTA procedure and the PCB procedure resulted in significantly more samples with no bacteria growth than the TTA procedure. To address the possibility that the volume of tracheobronchial secretion obtained by PCB was insufficient as a microbiological sample, a sterile, double-sheathed, protected aspiration catheter (PAC) was developed. Comparisons were made between TTA and PAC aerobic microbiology culture results from 18 pneumonic foals and weanlings. There were no significant differences between the PAC and TTA procedures with respect to the number of bacteria isolates. It was concluded that the PAC technique may be used as an alternative to TTA for isolation of equine pulmonary bacteria and may be the preferred procedure because of the reduced risk of complications associated with the TTA.

Animals↗