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Biomedical subjects

R Knight

Publications and source records attributed to R Knight.

At least 37 records · Page 2Linked to original sources
PubMed1989

Reduction of hyperthermic ischemic acidosis by a conditioning event in cats.

We investigated the effects of multiple episodes of cerebral ischemia on intracellular brain pH using in vivo phosphorus-31 nuclear magnetic resonance spectroscopy. Four cats were subjected to two 16-minute episodes of complete global cerebral ischemia 6 hours apart; the second episode occurred under hyperthermic conditions (mean +/- SD body temperature 40.8 +/- 0.4 degrees C). Intracellular pH in these four cats was compared with that in nine cats subjected to a single 16-minute episode of complete global cerebral ischemia under hyperthermic conditions (mean +/- SD body temperature 40.6 +/- 0.2 degrees C). Intracellular pH during hyperthermic recirculation was significantly (p less than 0.03) greater in cats subjected to a previous ischemic event than that in cats subjected to only a single hyperthermic ischemic event. We speculate that the induction of heat shock proteins by an initial ischemic event may protect brain tissue from further ischemic insult.

Acidosis↗
PubMed1989

Creutzfeldt-Jakob disease.

Creutzfeldt-Jakob disease is a 'slow virus' illness usually presenting as a rapidly progressive dementia. Although rare, its laboratory and accidental transmission has given it great theoretical importance. However, the infective agent remains mysterious and it is not known how, or even whether, natural transmission occurs. Clinical diagnosis is difficult, treatment unfortunately unsuccessful and special precautions are necessary in dealing with potentially infectious material.

Chronic Disease↗
PubMed1989

A study of knowledge, attitudes and practices (KAP) of a rural community on malaria and the mosquito vector.

A study of malaria on the Kano Plain, Kisumu District, Western Kenya, was carried out between April and August, 1985. The study included a knowledge, attitudes and practices (K.A.P.) survey on malaria illness and the mosquito vector. Overall knowledge about malaria illness was found to be good. However, treatment and prevention practices of malaria were found to be poor. Knowledge of the mosquito and its relationship to malaria was found to be high. Knowledge of methods of prevention of mosquito bites was also found to be high but actual use of the methods was low. Knowledge of traditional methods of prevention of mosquito bites was also found to be high. Actual use was again found to be low.

Gastric Acid↗
PubMed1988

Creutzfeldt-Jakob disease in England and Wales, 1980-1984: a case-control study of potential risk factors.

An attempt was made to ascertain all cases of Creutzfeldt-Jakob disease occurring in England and Wales during the 5 year period 1980-1984. The mean annual mortality rate was 0.49/million; women were more frequently affected than men. The age-specific mortality rate reached a peak in the seventh decade. A case-control study involving 92 of the 122 definite and probable cases ascertained failed to confirm the reality of previously suspected aetiological agents in the environment. Although there was no confirmed instance of familial Creutzfeldt-Jakob disease in the case-control study, dementia in close relatives was significantly more common than in controls.

Adult↗
PubMed1988

Effect of mild hyperthermia on recovery of metabolic function after global cerebral ischemia in cats.

We investigated the effect of mild whole-body hyperthermia before and after 16 minutes of global cerebral ischemia on metabolic recovery during recirculation in cats using in vivo phosphorus-31 nuclear magnetic resonance spectroscopy. Hyperthermia (temperature 40.6 +/- 0.2 degrees C) was induced greater than or equal to 1 hour before ischemia and was maintained during 1.5-2 hours of recirculation in nine cats; four cats were subjected to hyperthermia without cerebral ischemia, six to hyperthermia during recirculation (after return of intracellular pH to preischemic values), and 14 to normothermic ischemia and recirculation. Our data indicate that preischemic hyperthermia results in an intracellular cerebral pH during recirculation significantly lower than that in normothermic cats. In hyperthermic cats beta-ATP and phosphocreatine (PCr) concentrations and the ratio of PCr to inorganic phosphate failed to return to preischemic levels during recirculation in contrast to normothermic cats. Hyperthermia without ischemia and hyperthermia during recirculation had no significant effect on intracellular pH. Thus, preischemic hyperthermia has a detrimental effect on metabolic recovery after transient global cerebral ischemia.

Acidosis↗
PubMed1987

The importance of list size and consultation length as factors in general practice.

It is commonly believed that longer consultations are essential to better care and that this can only be achieved by lowering list sizes. The results of a survey of general practitioner trainers show that, on average, the time given to each patient was longer when general practitioners had lower list sizes, but that for a substantial minority of doctors list size played no part. Although the evidence is inconclusive, patients registered with lower list size general practitioners consulted more and received prompter attention. Doctors with smaller lists worked shorter hours and felt less overworked. However most of the correlates were weak owing to great individual differences of practice style between general practitioners. If a case for lower list sizes is to carry force, stronger evidence is needed that patients will receive more of their general practitioners' attention.

Appointments and Schedules↗
PubMed1986

A diurnal rhythm in proopiomelanocortin messenger ribonucleic acid that varies concomitantly with the content and secretion of beta-endorphin in the intermediate lobe of the rat pituitary.

The present study investigated whether diurnal variations in the secretion of alpha MSH and beta-endorphin from the intermediate lobe (IL) of the pituitary are associated with parallel changes in the synthesis of mRNA specifically encoding proopiomelanocortin (POMC). The results demonstrate that concomitant diurnal variations occur in both plasma and IL concentrations of immunoreactive beta-endorphin and alpha MSH. Plasma and IL peptide levels were relatively constant during daylight hours (0600-1800 h), but increased after the onset of darkness and reached maximal concentrations at 0200 h. To examine the possibility that this diurnal rhythm in the content and secretion of POMC-derived peptides resulted from diurnal changes in the biosynthesis of POMC, the concentration and rate of synthesis of POMC mRNA were examined. POMC mRNA levels were elevated during the dark period, reaching a maximum level at 0200 h that was 2-fold higher than that occurring during the light period. POMC mRNA synthesis, determined by measuring the number of RNA polymerase II complexes transcribing the POMC gene in isolated cell nuclei, also varied diurnally, with maximum transcription rates occurring at 1800 h, thus preceding maximal increases in POMC mRNA content and POMC peptide secretion by 8 h. Together, these data indicate that diurnal variations in the content and secretion of POMC-derived peptides are associated with parallel changes in POMC mRNA concentrations and are preceded by similar changes in POMC gene transcription.

Animals↗
PubMed1986

Ethological studies of depressed patients.

The use of ethological methods for characterising the non-verbal behaviour of depressed patients and quantifying change during treatment is described. Approximately 150 individual motor patterns--expressions, gestures and movements--have been defined and this element list provides the basis for encoding video-recordings of interactions. Data quality is controlled by inter- and intra-observer comparisons and by a split-screen technique which simultaneously displays a computer animation of a data file and the original video-recording. Two investigations of the characteristics of non-verbal behaviour in Depression are discussed. The first showed that the frequency and duration of many items of behaviour of depressed patients interviewed soon after admission to hospital differed significantly from matched controls. Recordings of an interview at an intermediate point in treatment showed a reduction in these differences and they had disappeared when examined shortly before discharge. The second study was of mothers suffering from Post Natal Depression who were interviewed once. This study provided evidence that quantification of non-verbal behaviour can distinguish between diagnostic subcategories and showed some of the fine detail of behaviour which can be revealed in this way.

Animals↗
PubMed1985

Effect of beta-blockers on psychomotor performance in normal volunteers.

The effects of beta-adrenergic receptor antagonists on psychometric tests including vehicle handling, choice reaction time, and kinetic visual acuity (KVA), are reviewed. The beta-blockers had little effect on the performance tests, with the unexplained but reproducible effect of enhanced KVA performance with atenolol. Although the beta-blockers had little effect on performance tests they were shown to have psychotropic effects in normal volunteers. The reasons for the conflicting evidence concerning the effect of these drugs on performance tests is discussed in relation to the present experiments and to variables that may influence response. It is concluded that one should use tests that are as independent as possible from potentially confounding variables. The use of evoked potentials in the electroencephalogram is one such test. A preliminary study is described in which the effects of beta-blockers were detected using visual evoked responses on the electroencephalogram.

Adolescent↗
PubMed1984

Cytogenetic effects of cyclamates.

PHA-stimulated human peripheral lymphocytes were used as a model system for assessing the in vitro effects of calcium cyclamate. Techniques of autoradiography, cytological staining, cell counting, liquid scintillation and karyotyping were used to study the cytogenetic damage and biochemical effects of calcium cyclamate when assayed in 24 hour intervals for 96 hours. The cells were exposed to 10(-2) and 10(-3) molar concentrations of calcium cyclamate in TC 199 medium with fetal calf serum and antibiotics. These studies were carried out in three (3) phases. Phase I was primarily orientation studies of the effects of cyclamates and included running preliminary test checks, the establishment of parameters of dosage, assessing growth patterns and selecting key chromosomal aberrations. Sixty four (64) of the metaphase spreads showed morphologically detectable changes and aberrations. It was also noted that the addition of cyclamate increased mitotic rate of lymphocyte cells in cultures. Phase III arranged research designs to determine more precise characterization of chromosomal observations and morphological effects. Among other findings it was noted that of 13 types of observations only ten were found in the experimental group. The introduction of cyclamates increased the stability of the leucocyte cultures. These studies reinforced the findings on the increase of mitotic rate. Phase III extended protocols to include autoradiography and scintillation counting. It was determined that calcium cyclamate impaired the synthesis of deoxribonunucleic acid (as depicted by decreased incorporation of tritiated thymidine), reduced grain counts in autoradiographs and increased chromosome aberrations in cyclamate treated PHA stimulated peripheral blood lymphocytes in vitro. Morphological changes and growth rates showed significant effects. These studies indicate that calcium cyclamate has variable significant effects on leucocytes growth and chromosome morphology.

Autoradiography↗
PubMed1984

Diazepam/beta-adrenoceptor antagonist interactions.

The effects of diazepam on the pharmacokinetics and pharmacodynamics of two lipophilic beta-adrenoceptor antagonists (propranolol and metoprolol) and a hydrophilic beta-adrenoceptor antagonist (atenolol) were compared in 12 subjects. Administration of propranolol and metoprolol produced small increases in the AUC0-8h for diazepam compared with placebo (P less than 0.05 for metoprolol). Atenolol had no significant effect on the AUC0-8h for diazepam. The increase in the AUC0-8h was accompanied by increases in the plasma concentrations of N-desmethyldiazepam. Diazepam had no significant effect on the pharmacokinetics of either propranolol or atenolol. The pharmacokinetic interaction could be attributed to inhibition of diazepam metabolism by the lipophilic beta-adrenoceptor antagonists. The pharmacodynamic studies showed that when compared with placebo or atenolol there was a significant impairment of kinetic visual acuity (KVA) when diazepam was co-administered with metoprolol. Although there was a significant correlation (P less than 0.02) between plasma concentrations of diazepam and impairment of KVA, the pharmacodynamic interactions may not be due solely to the small pharmacokinetic interaction observed.

Adolescent↗
PubMed1983

The effect of free and protected oils on the digestion of dietary carbohydrates between the mouth and duodenum of sheep.

Sheep fitted with rumen and re-entrant duodenal cannulas were given diets of approximately 200 g hay and 400 g concentrate mixture alone, or supplemented daily with 40 g linseed or coconut oils free or protected with formaldehyde-casein in a 5 x 5 Latin-square arrangement. Chromic oxide paper was given as a marker at feeding time and passage to the duodenum of neutral-detergent fibre (NDF) and different sugars were estimated from the values for constituent:marker at the duodenum. Contributions of microbial carbohydrates to these flows were estimated from amounts of RNA present. The carbohydrate composition of mixed rumen bacteria from sheep rumen digesta were similar regardless of diet. Of the sugars entering the duodenum all the rhamnose and ribose and 0.51, 0.24 and 0.35 of the mannose, galactose and starch-glucose respectively, were contributed by the microbes. Virtually all the arabinose, xylose and cellulose-glucose were contributed by the diet. For sheep receiving the basal ration, coefficients of digestibility between mouth and duodenum, corrected where necessary for microbial contribution, were 0.95, 0.66, 0.67, 0.62, 0.45 and 0.51 for starch-glucose, mannose, arabinose, galactose, xylose and cellulose-glucose respectively. Corresponding values when free-oil-supplemented diets were given were 0.95, 0.55, 0.38, 0.55, 0.01 and -0.02 respectively. Values for diets supplemented with linseed oil or coconut oil did not differ significantly. Addition of protected oils to the basal feed also resulted in depressed digestibilities of dietary structural sugars but to a far lesser extent than those observed with the free oils. Apparent digestibility of NDF was altered in the same direction as those of the main structural sugars, averaging 0.50, 0.17 and 0.29 in animals receiving the basal, free-oil-supplemented or protected-oil-supplemented diets respectively. The reasons for the difference between NDF and discrete carbohydrate analytical totals are discussed.

Animals↗
PubMed1983

The influence of polycyclic hydrocarbons on the activity of NAD(P)H-dehydrogenating enzymes in rat thymus. A biochemical and histochemical study.

The action of benzo(a)pyrene, 3-methylcholanthrene and 7,12-dimethylbenzo(a)anthracene in the activity of the rat thymus D-T diaphorase (EC 1.6.99.2) and the NAD(P)H cytochrome C (EC 1.6.99.3) reductases of particulate fractions were studied in intact and adrenalectomized animals. These polycyclic hydrocarbons increased severalfold the activity of the D-T diaphorase in intact and adrenalectomized animals. The activities of the particulate enzymes were not affected by the carcinogens. Dicumarol suppresses the inducing effects of benzo(a)pyrene and adrenalectomy does not influence the inducing effects of benzo(a)pyrene and 3-methylcholanthrene. The histological distribution of the enzyme NAD(P)H-nitroblue tetrazolium reductase was studied and a marked increase in its activity in lymphocytes, macrophages and epithelial cells was found after the administration of the carcinogens.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1983

Recognition and regulation of progenitor marrow elements by NK cells in the mouse.

The cytotoxicity of radiolabelled YAC-1 target cells by natural killer (NK) cells from the spleens of immunocompetent CBA mice is inhibited by unlabelled YAC-1 competitor cells, but not by resting bone marrow from syngeneic or allogeneic adult mice. Rapidly proliferating haemopoietic cells recovered from the spleens of lethally irradiated, bone marrow-reconstituted CBA mice, however, compete strongly in the NK assay. The competitive ability of early regenerating marrow correlates with the presence of an increased percentage of morphologically immature cells of mixed lineages. Competition declines in reconstituted spleens recovered more than 10 days after engraftment, as the proportion of immature elements falls towards that of resting marrow. Although the numbers of unlabelled YAC-1 cells required to produce equivalent competition of unstimulated and interferon-activated NK killing are similar, 10 times fewer regenerating marrow competitors compete cytotoxicity by unstimulated NK effectors to the same degree as interferon activated cells. The numbers of granulocyte-macrophage colonies formed in soft agar by regenerating marrow is also influenced by prior incubation of the marrow cells with NK effector populations. Spleen cells from homozygous athymic mice produce the same effect as cells from their heterozygous littermates. These data suggest that NK cells recognize and regulate the differentiation of progenitor elements within the marrow.

Animals↗