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Biomedical subjects

R Mitchell

Publications and source records attributed to R Mitchell.

At least 217 records · Page 12Linked to original sources
PubMed1991

Characterization of exopolymers of aquatic bacteria by pyrolysis-mass spectrometry.

Exopolymers from a diverse collection of marine and freshwater bacteria were characterized by pyrolysis-mass spectrometry (Py-MS). Py-MS provides spectra of pyrolysis fragments that are characteristic of the original material. Analysis of the spectra by multivariate statistical techniques (principal component and canonical variate analysis) separated these exopolymers into distinct groups. Py-MS clearly distinguished characteristic fragments, which may be derived from components responsible for functional differences between polymers. The importance of these distinctions and the relevance of pyrolysis information to exopolysaccharide function in aquatic bacteria is discussed.

Carbohydrates↗
PubMed1991

Biofilms and the survival of opportunistic pathogens in recycled water.

Microorganisms are likely to develop an organic film on pipes, water reservoirs and filters used for waste water reclamation during extended missions in space. These biofilms can serve to protect and concentrate potentially pathogenic microorganisms. Our investigation has emphasized the survival strategy of opportunistic pathogenic bacteria in distilled water. Pseudomonas aeruginosa and Staphylococcus aureus were used as test organisms. Cultures were incubated at 10 degrees, 25 degrees, and 37 degrees C. No viable Staphylococcus cells were detected after the first week of incubation. P. aeruginosa, however, survived in distilled water up to 5 months at all three temperatures tested. The starved cells were able to form a biofilm layer on stainless steel. The cells exhibited a negative surface charge. The charge may be involved in the adhesion of this bacterium to metal substrata. We are currently investigating the importance of adhesion in the survival of this and other potential human pathogens found in water recycling systems.

Bacterial Adhesion↗
PubMed1991

Follicle-stimulating hormone-dependent estrogen secretion by rat Sertoli cells in vitro: modulation by calcium.

We have investigated the role of Ca2+ in the control of FSH-induced estradiol secretion by Sertoli cells isolated from 8-10 days old rats. Exogenous Ca2+ (4-8 mmol/l) inhibited FSH-stimulated E2 secretion such that, with 8 mmol/l Ca2+ and FSH (8 IU/l) E2 secretion decreased from 2091 +/- 322 to 1480 +/- 84 pmol/l (p less than 0.002), whilst chelation of Ca2+ in the culture medium with EGTA (3 mmol/l) increased E2 secretion from 360 +/- 45 to 1242 +/- 133 pmol/l) in the absence of FSH. Further, EGTA (3 mmol/l) markedly potentiated FSH (8 IU/l), forskolin (1 mumol/l) and dibutyryl cAMP (1 mmol/l)-stimulated E2 secretion. Addition of the Ca2+ ionophores, ionomycin (2-5 mumol/l) and A23187 (2 mumol/l), inhibited FSH (8 IU/l)-stimulated E2 secretion by greater than 80%. The effect of ionomycin was totally reversible, whereas that of A23187 was irreversible. Ionomycin (5 mumol/l) had no effect on EGTA-induced E2 secretion in the absence of FSH, but reduced EGTA-provoked E2 secretion by 59% in the presence of FSH (8 IU/l). Similarly, forskolin- and dibutyryl cAMP-provoked E2 production was inhibited 46-50% by ionomycin (5 mumol/l). We conclude that FSH-induced E2 secretion from immature rat Sertoli cells is modulated by intra- and extracellular Ca2+.

Animals↗
PubMed1991

Inhibition of protein kinase C by staurosporine increases estrogen secretion by rat Sertoli cells.

We have examined the effect of inhibition of protein kinase C activity by staurosporine on estradiol secretion by Sertoli cells isolated from 8-10 days old rats. Staurosporine lead to a dose-related increase in estradiol secretion independent of FSH, such that with 100 nmol/l staurosporine basal estradiol levels increased 10-fold. The maximal response seen with staurosporine alone (100 nmol/l) or in combination with FSH (0.4-8 IU/l) was similar to that seen with a saturating dose of FSH (8 IU/l). There was no evidence of synergy between FSH and staurosporine. Activation of protein kinase C by phorbol 12,13 dibutyrate (10(-7) mol/l) resulted in a 53-74% inhibition of estradiol production provoked by FSH (8 IU/l), staurosporine (5-100 nmol/l) or staurosporine in combination with FSH. Staurosporine (5-100 nmol/l), in the absence or presence of FSH, was unable to overcome inhibition of estradiol secretion by phorbol ester, indicating the presence of at least two independent binding sites on protein kinase C for these molecules. Forskolin (1 mumol/l)- and dibutyryl cAMP (1 mmol/l)-stimulated estradiol secretion was inhibited by 31 +/- 5% and 64 +/- 5% respectively, by phorbol 12,13 dibutyrate (10(-7) mol/l). We conclude that FSH-induced estradiol secretion in immature rat Sertoli cells is affected by protein kinase C activity.

Alkaloids↗
PubMed1991

Kinetic evidence for two components in the priming effect of LH-releasing hormone in the rat.

The priming effect of LHRH on LH release from prooestrous rat hemipituitary glands in vitro was analysed by kinetic approaches. Concentration-response curves for LHRH-, K(+)- and ionomycin-induced LH release were constructed for initial exposure to the secretagogues and after 'priming' with a low dose of LHRH (100 pg/ml). These data were analysed by a non-linear curve-fitting programme to reveal the potency and maxima of the responses before and after priming. The parameters obtained from the curves fitted to the LHRH concentration-response curves showed that two changes had occurred as a result of priming. There was an increase in the maximum amount of hormone released and also a relatively greater ability for low concentrations of LHRH to cause release (increased potency). The data for K+ and ionomycin revealed only one change as a result of priming, an increase in the maximum amount of hormone available for release. The data indicate that LHRH, after self-priming, releases more hormone by at least two routes, one represented by a general increase in stimulus-secretion coupling (which is available to K+ and ionomycin), the other a specific up-regulation of signal transduction by the LHRH receptor-effector system.

Animals↗
PubMed1991

Type III collagen mutations cause fragile cerebral arteries.

Premature vascular aneurysms and fragility of cerebral arteries are commonly associated with type III collagen mutations and physical signs suggesting a generalized abnormality of connective tissue. Sometimes these traits are clearly genetically transmitted. Here we present seven examples of early cerebrovascular aneurysms or fragility including five examples of carotid cavernous sinus aneurysms. With one exception in which we suspect the mutation is too small to be detected, all of them had easily visible abnormalities of their type III collagen proteins. Further work in progress will eventually allow the characterization of their mutations at gene sequence level and will be followed by the ability to prevent transmission of the mutant genes in these families.

Adult↗
PubMed1991

The use of anti-D prophylaxis in the management of miscarriage in general practice.

Deaths from rhesus (Rh) haemolytic disease dropped steeply after anti-D immunoglobin became available for prophylaxis in Britain in 1969. Nevertheless, Rh incompatibility remains a cause of perinatal mortality and some unregistered fetal deaths before 28 weeks gestation. Some of these deaths are attributed to a failure to administer anti-D immunoglobin in the appropriate circumstances. The prophylactic administration of anti-D immunoglobin to Rh negative women or women whose Rh type was unknown was explored as part of a survey of the management of miscarriage in general practitioner training practices in the West of Scotland. Trainees were found to be the most likely, and general practitioners who had qualified before 1970 the least likely to offer anti-D prophylaxis. The advice of the Health Departments is currently unambiguous about the need to administer anti-D immunoglobin after miscarriage. The findings described here indicate the need to implement this advice more effectively until the question of first trimester sensitisation has been resolved.

Abortion, Spontaneous↗
PubMed1991

Biliary obstruction secondary to shrapnel.

Foreign bodies of the biliary tree represent infrequent causes of obstructive jaundice. We report a patient who developed biliary obstruction from metal shrapnel, 44 yr after a war injury. From our review of the literature, the syndrome of shrapnel-induced obstructive jaundice may occur many years after the initial injury. In the majority of patients, the missile lodges in the liver parenchyma, and migrates to the common bile duct. Complications from this injury include cholangitis, pancreatitis, and liver abscesses. As demonstrated by this case, computed tomography scan and endoscopic retrograde cholangio-pancreatogram may reliably detect this infrequent occurrence. With the development of therapeutic biliary procedures, many foreign bodies can be removed endoscopically. Thus, one should consider shrapnel-induced biliary obstruction in those patients with obstructive jaundice and prior combat injury.

Cholangiopancreatography, Endoscopic Retrograde↗
PubMed1990

Antigen expression from the ribosomal DNA repeat unit of Giardia intestinalis.

The amitochondrial human intestinal parasite Giardia intestinalis is regarded to be the most ancient living example of single-celled eukaryotes and should display primitive features of pre-metazoan gene regulation. Characterization of E. coli clones which express Giardia antigens from plasmid vectors has revealed that an antigen is encoded by the rDNA repeat unit from the strand complementary to that encoding the rRNAs. The open reading frame (ORF) originates in the spacer region between the small (SS) and large (LS) subunit rRNA genes and terminates within the LS rRNA gene. The promoter region of this ORF has characteristics of both RNA polymerase (pol) II and pol III regulatory sequences, suggestive of gene regulation before these different promoter types evolved. The rDNA repeat unit is located on multiple chromosomal sites which are different in each isolate, although the electrophoretic karyotypes appear very stable in Giardia from both human and animal sources.

Amino Acid Sequence↗
PubMed1990

The involvement of neurokinin receptor subtypes in somatosensory processing in the superficial dorsal horn of the cat.

As well as substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) have recently been found in the superficial dorsal horn of the spinal cord; NKA originating mainly in fine primary afferents. We have investigated the effects of these tachykinins and a range of analogues on somatosensory responses of single identified dorsal horn neurons, when applied ionophoretically to the region of the substantia gelatinosa. Behavioural reflex tests of thermal nociception were carried out in parallel. The role of NK-1, NK-2 and NK-3 receptors was addressed. NK-1-selective agonists attenuated the non-nociceptive responses of identified multireceptive spinocervical tract (SCT) neurons. Of the endogenous tachykinins, both SP and NKB (a weak NK-1 agonist) showed this effect. No role for NK-3 receptors was identified in our experiments. NK-2-selective agonists (including NKA) caused a unique and selective facilitation of thermal nociceptive responses. NKA also reduced reflex response latency in tail-flick and hot plate tests. NKA as a primary afferent transmitter may thus be involved in mediating or facilitating the expression of thermal nociceptive inputs in the substantia gelatinosa. NKA and SP could be considered as acting in concert in the superficial dorsal horn in an effectively pro-nociceptive modulatory role. Evidence from receptor-selective antagonists supports that obtained with agonists for the roles of particular NK receptors in somatosensory processing. NK-2, but not NK-1 or NK-3 antagonists attenuated endogenous thermal nociceptive responses, supporting the hypothesis that an NK-2 agonist (such as NKA) may normally participate in expression of thermal nociception in the superficial dorsal horn. Behavioural experiments showing increased response latencies with a putative NK-2 selective antagonist further supported the involvement of NK-2 receptors in thermal nociception.

Animals↗
PubMed1990

Rapid periarticular bone loss in rheumatoid arthritis. Possible promotion by normal circulating concentrations of parathyroid hormone or calcitriol (1,25-dihydroxyvitamin D3).

For approximately 2 years, bone loss was measured in women with early stages of rheumatoid arthritis (RA) and in control subjects, using serial computed tomography and dual photon absorptiometry. Rapid trabecular bone loss from the distal radius was observed in the RA patients but not the controls. The bone loss correlated with initial plasma levels of parathyroid hormone and 1,25-dihydroxyvitamin D3 (calcitriol) concentrations. It has been suggested that these humoral factors may interact with cytokines or other mediators produced in the adjacent wrist joint. Losses of the cortical bone of the radial midshaft and the lumbar spine were modest and were comparable in the 2 groups. Indices relating to both bone formation and bone resorption predicted bone loss at these 2 sites, but changes in the parathyroid hormone and calcitriol concentrations did not.

Absorptiometry, Photon↗
PubMed1990

DNA fingerprinting of the intestinal parasite Giardia duodenalis with the M13 phage genome.

A DNA fingerprint procedure has been established for the intestinal parasite, Giardia duodenalis. This permits the identification of individual strains from both human and animal sources. Analysis of strain movement, resurgence and variation is now possible. The fingerprint probe is based on the tandem repetitive sequence found in bacteriophage M13 which hybridizes to a set of hypervariable polymorphic minisatellite sequences found in higher eukaryotes. This probe recognizes a weakly homologous set of hypervariable regions in the Giardia genome to provide a DNA fingerprint comparable to those seen in higher eukaryotes.

Animals↗