Biomedical subjects

M Murray

Publications and source records attributed to M Murray.

At least 217 records · Page 12Linked to original sources

PubMed1995

Identification of a reversible component in the in vitro inhibition of rat hepatic cytochrome P450 2B1 by parathion.

Cytochrome P450 (P450) enzymes are inactivated in suicidal fashion during microsomal parathion oxidation. In the present study, two distinct components of the inhibition of the phenobarbital (PB)-inducible P450 2B1 by parathion were characterized. Here we report for the first time that low concentrations of parathion potently and reversibly inhibited, but did not inactivate, 2B1. In contrast, the previously described inactivation process occurred only at considerably higher parathion concentrations, at which concentrations enzyme activity was already extensively inhibited. At low concentration, parathion was a competitive inhibitor of 2B1-mediated androstenedione 16 beta-hydroxylation (Ki = 0.44 +/- 0.07 microM) and of 7-pentylresorufin O-depentylation (Ki = 0.40 +/- 0.03 microM) in microsomes from PB-pretreated rats and was similarly effective against androstenedione 16 alpha- and 16 beta-hydroxylation catalyzed by purified 2B1. Although preincubation of higher concentrations of parathion (> 5 microM) with NADPH-supplemented microsomes from PB-pretreated rat liver decreased holo-P450, heme loss was not observed near the Ki values. Instead, half-maximal loss of P450 occurred at 6 microM and at 9 microM parathion in PB-pretreated microsomes and in the reconstituted system, respectively. Parathion metabolism was efficient in PB-microsomes (Km values for 4-nitrophenol and paraoxon formation were 13 microM and 10 microM, respectively) and in the reconstituted system (corresponding Km values were 19 microM and 14 microM). Thus the constants for P450 inactivation and for parathion metabolism were similar and were at least 15-fold greater than the Ki values for the reversible process.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Virtual reality-multimedia synthesis: next-generation learning environments for medical education.

The Learning Resources Center of the University of California, San Diego School of Medicine has begun to investigate the potential of virtual reality (VR) as a tool for medical education. We are currently integrating VR with communications, animation, and visualization technologies to form a hybrid learning and training environment. Our program development reflects a curriculum-based strategy with emphasis on instructional objectives and educational outcomes. Demonstrated need, feasibility of a technology-based solution, and appropriateness of resource allocation are primary considerations. As the VR world is built, comparative analyses are being made of control strategies, display options, and interface design.

Computer Simulation↗

PubMed1994

Suppression of the constitutive microsomal cytochrome P450 2C11 in male rat liver during dietary vitamin A deficiency.

The effect of dietary vitamin A deficiency on hepatic microsomal cytochrome P450 (P450) and associated oxidase activities was examined in the male rat. Intake of a deficient diet by weanling rats over 10 weeks led to a pronounced decline in hepatic and serum vitamin A concentrations to levels that were beneath the limits of detection. These changes occurred concurrently with a decrease in total microsomal P450 to 77% of vitamin A adequate control. Measurement of microsomal androstenedione metabolism revealed respective decreases in 16 alpha- and 6 beta-hydroxylation pathways to 61 and 71% of adequate control; 7 alpha-hydroxylation was not significantly decreased. Immunoquantitation of the principal catalyst of steroid 16 alpha-hydroxylation, the androgen-dependent P450 2C11, indicated a significant decrease in the microsomal content of the enzyme to 78% of control (13.7 +/- 0.9 ng/micrograms protein in deficient rat liver versus 17.5 +/- 0.5 in adequate control; P < 0.005). Serum testosterone appeared lower in vitamin A deficient male rats, but did not attain statistical significance. Administration of a diet containing excess vitamin A (500 IU/g) to rats for 10 weeks produced marked increases in hepatic vitamin A stores, but did not increase P450 2C11 activities. Thus, the expression and function of P450 2C11 is not related directly to hepatic vitamin A levels. The trend toward lower circulating androgen levels in male rats maintained on the deficient diet for 10 weeks may have a role in P450 2C11 down regulation, but other regulatory factors may also be disrupted in these animals.

Androstenedione↗

PubMed1994

Pretranslational down-regulation of male specific hepatic P450s after portal bypass.

Diversion of portal blood away from the liver in the portal vein ligated (PVL) male rat results in dysfunction of the hypothalamo-pituitary-gonadal axis, as reflected by an increase in circulating oestradiol, a decrease in serum testosterone and decreased expression of the male-specific cytochrome P450 2C11 in hepatic microsomes. The present study assessed whether there was a decline in the hepatic concentrations of mRNA species corresponding to male-specific P450s and whether female-specific hepatic enzymes may be upregulated after PVL. In microsomes from PVL male rat liver the activities of P450s 2C11 and 3A2 (androstenedione 16 alpha- and 6 beta-hydroxylation, respectively) were decreased to 45% (P < 0.001) and 43% (P < 0.002) of control. Slot blotting revealed a decline in the mRNAs for P450 2C11 and 3A2 to 46 +/- 7 and 27 +/- 4% of respective control (relative to beta-actin mRNA). In contrast, mRNAs for the female specific P450 2C12 and delta 4-ketosteroid-5 alpha-oxidoreductase were unchanged from control (100 +/- 13% and 122 +/- 28%, respectively). P450 2C12 protein was not detected in either control or PVL male rat liver but a slight increase in the rate of 5 alpha-dihydrotestosterone formation was noted after PVL (2.95 +/- 0.40 vs 1.00 +/- 0.22 nmol/min/mg protein, P < 0.05; corresponding, respectively, to 30 and 10% of the activity in female liver microsomes). These studies indicate that the male-specific P450 2C11 and 3A2 are down-regulated at a pretranslational level whereas upregulation of the female-specific enzymes P450 2C12 and delta 4-ketosteroid-5 alpha-oxidoreductase does not occur after PVL. Thus, the endocrine effects of portal bypass result in biochemical demasculinization, but not feminization, of hepatic enzymes involved in steroid biotransformation. Because male-specific P450s are effective steroid hydroxylating enzymes, their down regulation after PVL would significantly decrease hepatic androgen extraction.

Androstenedione↗

PubMed1994

Inhibition of microsomal 17 beta-hydroxysteroid oxidoreduction activities in rat liver by all-trans-, 9-cis- and 13-cis-retinoic acid.

Retinoids and steroid hormones mediate their biological effects through nuclear receptors. However, retinoids may alter the intracellular availability of ligands for steroid receptor activation by modulating the activity of biotransformation enzymes. This study investigated the modulation of NAD(H)-linked steroid oxidoreductases in rat hepatic microsomes by retinoids. 13-cis-Retinoic acid inhibited testosterone 17 beta-dehydrogenation (Ki 2.4 +/- 0.5 microM; Km/Ki ratio 0.34 +/- 0.06) but androstenedione reduction was less susceptible to inhibition (Ki 27 +/- 13 microM; Km/Ki ratio 0.045 +/- 0.12). All-trans-retinoic acid was less potent than the 13-cis-isomer and 9-cis-retinoic acid was of intermediate potency. In vivo administration of all-trans-retinoic acid (60 mg/kg i.p. for 7 days) decreased hepatic microsomal oxidoreduction activity, but exposure over shorter periods and 13-cis-retinoic acid were without effect. Thus, all-trans-retinoic acid elicits direct inhibition and may also alter the normal regulation of the oxidoreductase under certain conditions. Three geometric isomers of retinal were potent inhibitors of testosterone dehydrogenation (IC50s approximately 6 microM), but were ineffective against androstenedione reduction. These findings suggest that certain anti-hormonal effects of retinoids may be attributable in part to modulation of endobiotic biotransformation prior to receptor binding and activation.

17-Hydroxysteroid Dehydrogenases↗

PubMed1994

The solution structures of the first and second transmembrane-spanning segments of band 3.

We have studied the structures of synthetic peptides which correspond to the proposed first and second membrane-spanning segments of the human red cell anion transporter (band 3). The peptides, which were acetylated at their N-termini and amidated at the C-termini, comprise the 20 amino acids of residues 405-424 and 21 amino acids of residues 436-456 of the human band 3 sequence. The solution structures of the peptides in trifluoroethanol were studied by two-dimensional NMR spectroscopy. Characteristic NOEs were observed indicating that the peptides adopted a predominantly alpha-helical structure in trifluoroethanol solution. Dynamical simulated annealing using the program XPLOR was employed for the structure calculations. The amide exchange rates in trifluoroethanol have also been measured and are consistent with an alpha-helical structure for the peptides.

Acetylation↗

PubMed1994

Retinal dehydrogenation and retinoic acid 4-hydroxylation in rat hepatic microsomes: developmental studies and effect of foreign compounds on the activities.

All-trans-retinoic acid (RA) regulates the transcription of a number of mammalian genes and is therefore important in the control of many cellular processes. RA is formed and deactivated within the cell so that biotransformation modulates RA availability. This study investigate the relationship between the formation of RA from retinal and its metabolism by 4-hydroxylation in rat hepatic microsomes. From kinetic studies the Michaelis constants for RA formation and 4-hydroxylation were 52 and 24 microM, respectively, and the maximal reaction velocities were 33 and 136 pmol/min/mg protein, respectively. Thus, 4-hydroxylation was the more efficient process. In microsomes from 1-week-old rats, RA formation was very low (approximately 2 pmol/min/mg protein) but was several-fold greater in adults of both sexes (approximately 10 pmol/min/mg protein). In contrast, 4-hydroxylation was quantitatively more significant at all ages examined between 1 and 15 weeks; by 10 and 15 weeks a sexual dimorphism was apparent (M > F). Thus, the ratio of RA 4-hydroxylation to RA formation was comparatively large in microsomes from 1-week-old rats and declined to a stable value around 4-6 weeks of age. With the exception of dexamethasone, which decreased the activity, administration of foreign compounds to male rats had little effect on RA formation. Both dexamethasone and phenobarbital induced RA 4-hydroxylation but DMSO and beta-naphthoflavone were without effect. From these findings, 4-hydroxylation, particularly in very young animals, may be an effective means of controlling RA production. RA 4-hydroxylation, like other cytochrome P450 activities, was inducible in rat liver but no evidence was found for induction of the microsomal retinal dehydrogenase.

Aging↗

PubMed1994

Isolation and complete sequence of CBR, a gene encoding a putative cytochrome b reductase in Saccharomyces cerevisiae.

We have isolated and characterised a novel yeast gene, CBR (cytochrome b reductase), encoding a 35-kDa yeast novobiocin-binding protein. The predicted protein sequence of CBR displays considerable similarity to both plant nitrate reductases and mammalian cytochrome b5 reductases indicating that it is a putative member of the flavoprotein pyridine-nucleotide-cytochrome-reductase family. Disruption of CBR is not lethal under various growth conditions, suggesting the presence of some functional overlap with other reductases, possibly with the cytochrome P-450 reductase.

Amino Acid Sequence↗

PubMed1994

Transient and permanent patterns of expression of the low-affinity neurotrophin receptor in the interpeduncular nucleus of the rat.

There is a prominent cholinergic projection from the medial habenular to the interpeduncular nucleus (IPN) which develops postnatally. In this study we examined the developmental course of expression of the low-affinity neurotrophin receptor (LANR), a receptor that binds to all members of the neurotrophin family, in the IPN. Three systems express LANR in the IPN. The cholinergic habenular axons that project to the intermediate and central subnuclei of the IPN are immunoreactive only during the time that the axons are growing and forming characteristic crest synapses in the intermediate subnuclei. The dorsomedial (DM) subnuclei, which are neither cholinergic targets nor contain cholinergic neurons, develop LANR immunoreactivity postnatally and the expression remains high in the adult. The walls of the prominent system of arterioles and venules that penetrate the IPN and ascend through the intermediate subnuclei are strongly immunoreactivity during the time of active angiogenesis and retain detectable but diminished levels of immunoreactivity in the adult. The LANR immunoreactivity seen in the vessels is likely to be associated with the peripheral sympathetic axons that innervate the smooth muscle in the vessels. These three systems within the same nucleus, which differ in phenotype, develop neurotrophin receptor immunoreactivity contemporaneously but their levels of expression differ in the adult, suggesting that they are regulated in different ways, possibly by different members of the neurotrophin family.

Animals↗

PubMed1994

Identification, partial sequence and genetic analysis of mlpA, a novel gene encoding a myosin-related protein in Physarum polycephalum.

Studies of motility in Physarum polycephalum have concentrated on the well-defined actomyosin system in plasmodia. It is clear from recent genetic studies in lower eukaryotes that myosin is involved in a number of physiological processes in addition to the contractile functions previously ascribed to the classical type II myosins. Moreover, the myosin protein family has proved to be more complex than anticipated, with an increasing number of reported specialized isoforms. Although a myosin type II activity has been identified in both amoebae and plasmodia of P. polycephalum, and it has been inferred that these proteins undergo a phase-specific isoform switch during development, this phenomenon has not been analysed genetically. In an effort to understand the putative developmental expression of actomyosin-associated proteins, we isolated a 180-kDa protein from amoebae which is highly enriched, along with actin and myosin, in actomyosin preparations in the presence of mM concentrations of Mg++ ions and 10 mM of ATP. Using polyclonal antisera raised against pl80 we have cloned and sequenced a partial cDNA encoding a protein whose predicted amino-acid sequence indicates some similarity with the Dictyostelium discoideum myosin heavy-chain tail domain. Southern-blot and RFLP analyses indicate that the gene involved, designated mlpA (myosin-like protein), occurs in a single copy in the genome, is a novel Physarum gene and is expressed during amoebal and plasmodial growth and in the dormant forms of both these cell types.

Amino Acid Sequence↗

PubMed1994

Patterns of Trypanosoma vivax and T. congolense infection differ in young N'Dama cattle and their dams.

Trypanosome infection was detected by the dark ground/phase contrast buffy coat microscopic technique in N'Dama cattle in a high natural tsetse challenge situation in Zaire. The data were used to compare the pattern of infection in very young animals and in their dams, and to evaluate how the pattern evolved in calves from birth to maturity, and thereafter in the different age groups represented by their dams. Five hundred and fourteen calves were evaluated at 3 week intervals for an average of 26 months each, over varying periods between birth and 42 months of age. Two hundred and sixty nine dams had matching records from parturition to calf weaning at 10 months. One month after weaning, animals were equally infected with Trypanosoma vivax and Trypanosoma congolense. From then until 42 months, the proportion of time an animal was infected with T. vivax relative to T. congolense gradually decreased. In the dams this trend continued from 4 years to at least 8 years of age by which time T. vivax infection was only one-third that of T. congolense infection. This finding is regarded as strong evidence of the ability of N'Dama cattle, in this region of Africa, to acquire significant control of the development of parasitaemia following T. vivax infection but apparently not following T. congolense infection. Pre-weaner calves, grazing with their dams, appeared to have considerable protection from, or be more resistant to, both T. vivax and T. congolense infections compared with their dams and to their own immediate post-weaning situations.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1994

Quantitative phenotyping of N'Dama cattle for aspects of trypanotolerance under field tsetse challenge.

Matching animal health and performance data were recorded over the 2 year period from weaning at 10 months of age on 255 N'Dama cattle in a high natural tsetse challenge situation in Zaire. Four parameters that are regarded as possible indicators of trypanotolerance, species of trypanosomes detected, length of time parasitaemic, intensity of parasitaemia (parasitaemia score), and anaemic condition as estimated by packed cell volume (PCV) values, were measured and the relative effects of changes in these parameters on trypanocidal drug requirements and growth were assessed. The effects of species of trypanosome on drug requirements and growth were directly measurable. In the case of the other three indicators, the effects on drug requirements and growth that would be brought about by a change of one standard deviation in each were calculated. This allowed comparison of similar sized changes in these three indicators that are of necessity recorded in dissimilar units. Trypanosoma vivax and Trypanosoma congolense infections had equal effects on the number of trypanocidal drug treatments required, an average of 0.61 treatments being administered to each infected post-weaner. A reduction of one standard deviation (SD) in length of time infected reduced the number of treatments required by 0.23 or 36% and an increase of 1 SD in PCV reduced the number required by 0.27 or 43%. Changes in parasitaemia score were not important. In the case of growth, a T. congolense infection reduced growth by 12.4 g day-1 or 8% more than a T. vivax infection. A reduction of 1 SD in length of time infected increased growth by 9.8 g day-1 or 6.5%, a reduction of 1 SD in parasitaemia score increased growth by 9.0 g day-1 or 6.0%, and an increase of 1 SD in average PCV increased growth by 8.4 g day-1 or 5.6%. The necessity to simultaneously measure the four criteria is clearly indicated by their approximately equal effects on the final performance trait of daily liveweight gain. Thus, absence of information on any of these criteria would significantly affect the accuracy of the estimate of an animal's overall trypanotolerance phenotype in this central African situation and reduce the progress possible in production projects involving N'Dama cattle.

Anemia↗

PubMed1994

Genetic resistance to parasitic disease: particularly of resistance in ruminants to gastrointestinal nematodes.

There is substantial variation among individuals in susceptibility to a wide variety of parasitic diseases and part of this variation in susceptibility is due to genetic factors. The challenge now is to determine the best methods of using the variation to improve our understanding of parasitic infection and to reduce the ravages of parasitic disease. Scientific and commercial applications will depend upon the type of genetic variation. Variation among breeds can be easily exploited by a policy of breed substitution. Variation within a breed can be exploited by selective breeding to improve resistance to infection or to disease, but more work is needed to develop selection indices which are acceptable to livestock breeders. Identifying genes which contribute to the variation in resistance provides a better understanding of the mechanisms of resistance but more work is needed to determine if such genes, alone or in combination, account for a sufficient proportion of the variation in resistance to allow marker assisted selection. A comparison of responses in susceptible and resistant stock provides a powerful tool to distinguish among protective, irrelevant and pathological responses. These themes have been illustrated by three studies of gastrointestinal nematode infections in ruminants.

Animals↗

PubMed1994

Careers in health care management, Part 1: Attainment, expectations and aspirations.

The authors conducted a questionnaire survey of health care managers in Canada to learn more about their careers, work experiences and attitudes; and to determine whether their careers differed by such factors as sector of employment, gender, years of experience, education and family status. Major findings include: in teaching and community hospitals, men are more likely to fill chief executive officer (CEO) positions and women tend to be in middle management positions. More men than women in CEO positions reported incomes in the top range ($105,000). Men in CEO and senior management positions are more likely to be married and have children under 16 years of age living at home. Slightly more women than men were clinicians before becoming managers. Most respondents aspired to CEO or senior management positions. Implications for human resources practices are discussed.

Canada↗

PubMed1994

A segmental chronic pain syndrome in rats associated with intrathecal infusion of NMDA: evidence for selective action in the dorsal horn.

We explored the effects of chronic lumbar intrathecal NMDA infusion (mini-osmotic pumps) in Sprague-Dawley rats on motor and sensory axon integrity. Several different infusion protocols, each given over a 4 week period were examined: 0.15 M NMDA in phosphate buffered saline; phosphate buffered saline without NMDA; and 0.20 M magnesium sulfate plus 0.15 M NMDA; 0.35 M NMDA. In two additional protocols, 0.15 M NMDA or phosphate buffered saline were infused for a total of 8 weeks. Within 1-2 weeks of the onset of NMDA, but not phosphate buffered saline infusions, the rats exhibited irritability, circling, biting and excessive grooming resulting in loss of hair, and skin ulcerations from autotomy localized to lumbar and sacral innervated dermatomes. Co-infusion of NMDA with magnesium sulfate almost completely prevented these findings. The behavioural changes were not associated with abnormalities of sensory or motor conduction. Intrathecal infusion of NMDA induces a chronic "central" experimental pain disorder in rats, localized to the cord segment with the greatest exposure to the infusion, without involvement of peripheral sensory axons and sparing the axonal integrity of anterior horn cells.

Animals↗

PubMed1994

Dissociation of behavioral changes in rats resulting from lesions of the habenula versus fasciculus retroflexus and their possible anatomical substrates.

Lesions in either the habenula or its primary efferent pathway, the fasciculus retroflexus (FR), impaired avoidance responding. However, lesions of only the FR provided a persistent elevation of locomotor activity. Immunocytochemical study of the interpeduncular nucleus (IPN) through injection of retrograde tracers into the IPN and the overlying ventral tegmental area indicated that habenular lesions spared both rostral habenula and forebrain projections to the caudal midbrain, but these projections were axotomized by FR lesions. Rostral sparing of the habenula resulted in normal peptidergic staining in the IPN, and normal cholinergic innervation was absent. Performance of individual rats in behavioral tests was consistent with variations in anatomical sparing. Such considerations may account for previous discrepancies in functional effects of habenular lesions.

Animals↗

PubMed1994

Immune responses of elderly persons 4 years after receiving a live attenuated varicella vaccine.

Annually, for 4 years after a live attenuated varicella-zoster virus (VZV) vaccine was administered to 202 elderly (55 to > 87 years old) VZV-immune persons, the immune response of vaccinees was evaluated. Anti-VZV antibody levels were enhanced by vaccination for just 1 year. However, VZV-specific proliferating T cells in peripheral blood were increased in frequency from 1 in 68,000 to 1 in 40,000 at 1 year; VZV-responding T cells were still 1 in 51,000 4 years after vaccination. The calculated half-life of this enhanced immunity was 54 months. Age had little effect on response to the vaccine, but larger doses were associated with longer duration of enhanced immunity. Immunity in approximately 10%-15% of vaccinees, independent of dose, failed to increase with the vaccine. This might complicate the use of this vaccine for prevention or attenuation of herpes zoster in the elderly.

Age Factors↗

PubMed1994

Early embryonic development in the Djungarian hamster (Phodopus sungorus) is accompanied by alterations in the distribution and intensity of an estrogen (E2)-dependent oviduct glycoprotein in the blastomere membrane and zona pellucida and in its association with F-actin.

The luminal environment of the estrogen (E2)-dominated mammalian oviduct generates and sustains the environment in which the first embryonic cleavages take place. The objective of this study was to determine, by use of an antiserum against an E2-dependent sheep oviduct secretory glycoprotein (M(r) 90,000-92,000), whether the E2-dominated and pregnant oviduct of the Djungarian hamster (Phodopus sungorus) releases an antigenically related protein. If the protein was present, a secondary objective was to define its fate and association with filamentous-actin (f-actin) and chromatin patterns in early cleavage-stage embryos. Oviduct flushings containing embryos (1-cell fertilized, 2-, 4-, and 8-cells), and uterine flushings (> 16 cell embryos) were obtained from pregnant hamsters. Embryos were removed from flushings, and oviduct secretions were analyzed by Western blotting. The zona pellucida was removed with acid Tyrode's solution from approximately half of the 2-, 4-, and 8-cell embryos. Zona-intact and zona-free embryos were then fixed and subjected to triple immunofluorescence staining with an antiserum to the sheep oviduct protein, rhodamine phalloidin, and Hoechst 33258. An antigenically related protein M(r) 200,000) was detected in oviduct secretions of E2-treated, ovariectomized, and pregnant hamsters, and not in secretions from ovariectomized controls. In the zona pellucida of 1- and 2-cell embryos, the oviduct protein displayed an intertwining, reticular organization that was replaced by a diffuse and more intense accumulation in 4-, 8-, and > 16-cell embryos. In 2-cell embryos, punctate foci of the oviduct protein were distributed unevenly over the apical blastomere plasma membrane, forming patches in regions of f-actin exclusion, which were absent at later development stages. At the 4- and 8-cell stage of development, as blastomeres lost their spherical form by minimizing intercellular spaces, the oviduct protein took on a polarized arrangement and was intensely concentrated on membrane areas involved in cell-cell contact that were also the focus of f-actin. These data show that in early cleavage-stage hamster embryos, the intensity and pattern of staining for an E2-dependent oviduct protein (M(r) 200,000) that is released into the oviduct lumen during embryo transport can be distinguished on the basis of membrane f-actin display and blastomere number and shape. These events may mediate cellular processes related to blastomere cleavage, shaping, and/or adhesion that occur in the oviduct.

Actins↗