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Biomedical subjects

M H Johnson

Publications and source records attributed to M H Johnson.

At least 253 records · Page 14Linked to original sources
PubMed1986

The effect of vegetarian diets on plasma lipid and platelet levels.

Vegetarians have an apparent diminished risk for the development of ischemic coronary heart disease. This may be secondary to dietary effects of plasma lipids and lipoproteins, but platelets, which may also play a role, have also been observed to have aberrant functions in vegetarians. We measured plasma lipid and lipoprotein levels, platelet function, platelet fatty acid levels, and platelet active prostaglandins in ten strict vegetarians (vegans), 15 lactovegetarians, and 25 age- and sex-matched omnivorous controls. The most striking observations were a highly significant rise in platelet linoleic acid concentration and a decline in platelet arachidonic acid concentration in both vegetarian subgroups as compared with omnivorous controls. Serum thromboxane and prostacyclin levels as well as results of platelet aggregation studies did not differ among the groups tested. Cholesterol levels were significantly lower in both vegetarian groups as compared with controls, but plasma high- and low-density lipoprotein levels were lower only in the vegan subgroup as compared with omnivores. If diet produces these changes in platelet fatty acid and plasma lipid levels it may contribute to the decreased risk of coronary heart disease and possibly atherosclerosis in vegetarians.

Adult↗
PubMed1986

Mechanism of polar body formation in the mouse oocyte: an interaction between the chromosomes, the cytoskeleton and the plasma membrane.

The influence of mouse oocyte chromosomes on their immediate environment has been investigated following their dispersal by dissolution of the metaphase spindle with nocodazole. Small clusters of chromosomes become redistributed around the egg cortex in a microfilament-dependent process. Each cluster has the capacity, on removal from nocodazole, to organize a spindle that rotates to yield a polar body. In this process of spindle formation, the chromosome clusters are able both to promote tubulin polymerization in their vicinity and to recruit microtubule-organizing centres (MTOCs) which organize the polymerized tubulin into spindles. In addition each oocyte chromosome cluster, as well as the non-dispersed sperm-derived haploid group of chromosomes, induces a focal accumulation of subcortical actin (corresponding to a filamentous area devoid of organelles) and a loss of surface Concanavalin A binding activity (corresponding to a loss of surface microvilli) in the overlying cortex. This induction ceases with the formation of pronuclei whether or not the pronuclei migrate centrally. Pronuclear formation is sensitive to the action of nocodazole for up to 2-4 h postinsemination, and pronuclear migration is totally sensitive to the drug. If pronuclei are blocked in a peripheral location by nocodazole they are associated with an elevation in Con A binding activity of the overlying membrane which corresponds to an area of the surface rich in blebby microvilli.

Animals↗
PubMed1986

The timing of compaction: control of a major developmental transition in mouse early embryogenesis.

The effect of protein synthesis inhibitors on compaction of the 8-cell mouse embryo has been investigated. The effects observed depended upon the duration and time of drug application and on the features of compaction scored. Continuous application from the late 2-cell or early 4-cell stages allowed cell flattening and surface polarization to occur in most embryos and advanced development of these features in many of them. Cell coupling developed only when drug addition was delayed until the mid 4-cell stage, and cytoplasmic polarization developed only when drug addition was delayed until the late 4-cell stage. We suggest that control over the timing of compaction is achieved at a post-translational level via a global permissive change within the blastomeres of the embryo.

Animals↗
PubMed1985

Hemoglobin New Mexico: beta 100 (G2) Pro----Arg. A variant hemoglobin associated with erythrocytosis.

Hemoglobin New Mexico beta 100 Pro----Arg was found in a 4-year-old black male and represents a new mutation. The propositus is also heterozygous for Hb S. The variant shows high oxygen affinity, reduced cooperatively, and a lowered alkaline Bohr effect. Addition of allosteric effectors leads to improved cooperativity and a Bohr effect that is similar to that of Hb A. The high percentage of the variant (53.5%) and its increased oxygen affinity result in erythrocytosis in this patient. The hemoglobin level and packed cell volume values are elevated. In spite of these factors the patient appears healthy and shows no discomfort. The altered oxygen-linked properties of this variant can be related to the fact that the substituted residue contributes to the alpha 2 beta 1/alpha 1 beta 2 subunit interface, an area that is critical not only to the allosteric transitions between the oxy and deoxy states but also to stabilizing the hemoglobin tetrameer.

Child↗
PubMed1985

Effects of early experience on the development of filial preferences in the domestic chick.

Factors affecting the development of filial preferences in chicks were investigated. Four groups of chicks were hatched and maintained in darkness. When the chicks were 20-hr old, three of these groups were exposed to an overhead light ("primed") for .5 h. When 24-hr old, all groups were placed in running wheels for 2 hr. While in the wheels one group was exposed to a visually complex pattern, one group to diffuse overhead light, and the remaining two groups (one primed and one not primed) were in darkness. All chicks were then returned to a dark incubator until their preference for a red box or a stuffed jungle fowl was measured in a simultaneous choice test either 2 hr (Test I) or 24 hr (Test II) later. At Test I the chicks which had been exposed to the complex visual pattern showed a significant preference for the fowl. Chicks in the other groups showed no preference. At Test II all groups showed a significant preference for the fowl. The results of a second experiment suggested that the later emerging preference was related to the chicks experience in the running wheel. It was concluded that the preference for the fowl will develop in entirely dark-reared chicks that are allowed a period of time in a running wheel, but that this preference will appear earlier in chicks which have had experience of a complex visual pattern.

Animals↗
PubMed1985

Resistive NMR of brain stem gliomas.

The NMR and CT findings in 22 patients with primary brain stem tumors were compared to determine the value of each study in identifying, and delineating the extent and relationships of the tumor to brain anatomy. NMR was found to be distinctly superior to CT in showing involvement of the medulla and upper cervical cord. NMR eliminates the need for intrathecal enhanced metrizamide CT, and in the future should be the only initial diagnostic test needed for the evaluation of intrinsic brain stem tumors.

Adolescent↗
PubMed1985

Deswelling of the cornea after hypoxia.

Central corneal thickness changes were monitored in nine subjects who wore low water content hydrogel lenses of varying thickness for 3 h in the open and closed eye conditions. At the end of 3 h of lens wear, corneal deswelling to prelens thickness for the different levels of hypoxia was determined by pachometry performed every 5 min for the first 30 min, every 10 min for the next 40 min, and every 15 min thereafter. Examination of the individual deswelling profiles indicates (1) a biphasic response in those with corneal edema greater than 14%, and (2) a large portion of the deswelling occurred during the first 30 min, followed by a more gradual rate until baseline was reached. Small amounts of corneal edema (less than 5%) required up to 25 min to return to baseline, whereas 6 to 15% required 30 to 70 min, and 20% required 95 min. The time taken for the cornea to deswell to baseline was linearly related to the amount of corneal swelling (r = 0.88; p less than 0.0001).

Adult↗
PubMed1985

A dissection of the mechanisms generating and stabilizing polarity in mouse 8- and 16-cell blastomeres: the role of cytoskeletal elements.

Pairs of 8-cell or 16-cell blastomeres were cultured for up to 9 h after their formation from isolated 1/4 or 1/8 blastomeres respectively. Blastomeres were examined for the incidence and orientation of their surface polarity, as assessed by binding of FITC-Con A and by distribution of microvilli, and of their cytoplasmic polarity, as assessed by distribution of cytoplasmic actin, clathrin and a 100 kD antigen associated with the lysosomal/acid vesicle fraction of membranous organelles. The effect on polarity of incubating the pairs of cells in taxol, nocodazole, cytochalasin D or in a combination of nocodazole plus cytochalasin D for different parts of the incubation period was examined. Neither the development nor the stability of the surface polarity in 8-cell blastomeres was blocked by any treatment and only the use of CCD in combination with nocodazole affected the incidence of surface polarity appreciably. However, with some treatments, the form and position of the surface poles were modified. In the presence of microtubule inhibitors surface poles extended over a larger area of the cell surface, while exposure to CCD led to poles that were not opposite to the contact point between cells. In contrast to surface polarity, the development of cytoplasmic polarity was suppressed by both microtubule- and microfilament-inhibiting drugs, which also reversed it rapidly. In polar 16-cell blastomeres surface polarity was influenced in a similar manner to that of 8-cell blastomeres, only the combined use of cytochalasin D and nocodazole having any major effect. Polarization of clathrin in polar 16-cell blastomeres was inhibited almost completely by all drug treatments applied including cytochalasin D. The focal concentration of lysosomal antigen that occurs during the 16-cell stage was reduced only in the continuous presence of nocodazole plus cytochalasin D, but once established was not reversed appreciably by any drug. However, the localization of the lysosomal antigen to the basal region of polarized cells did not seem to occur in the presence of any drug. The dissociation of surface and cytoplasmic polarity revealed in these experiments leads us to conclude that either surface polarity is a prerequisite for the organization of cytoplasmic polarity, and mediates the latter via the cytoskeleton, or surface and cytoplasmic polarity develop by parallel but separate mechanisms.

Alkaloids↗
PubMed1985

Changes in the distribution of membranous organelles during mouse early development.

The unfertilized oocyte, fertilized egg and early embryo (2-cell to 16-cell) of the mouse have been examined immunocytochemically for the distribution of antigens associated with the endoplasmic reticulum, the lysosomal and acidic vesicle fraction (100 kD antigen), Golgi apparatus (135 kD antigen) and coated vesicles (clathrin). The distribution of these antigens has also been examined in isolated 8-cell and 16-cell-stage blastomeres of various ages and phenotypes. Endoplasmic reticulum is detected only weakly in the oocyte and egg, but is seen abundantly at later stages both in association with the nuclear membrane and evenly distributed throughout the cytoplasm, except in regions of cell:cell apposition from which it is excluded. Intracellular clathrin is associated with the spindle in mitotic and meiotic cells. During interphase, clathrin is distributed throughout the cell until the mid-8-cell stage when it is concentrated into the apical region of the cell under the region of membrane at which a surface pole of microvilli will form subsequently. Thus, the cytoplasmic polarization of clathrin precedes overt polarization at the surface. At mitosis, the clathrin relocates to the spindle and is distributed to both daughter cells. It resumes an apical location beneath the surface pole of microvilli in polar daughter 1/16 cells, but remains dispersed in apolar daughter 1/16 cells. Both the lysosomal and Golgi antigens are distributed throughout the cytoplasm until the early 16-cell stage. In pairs of 16-cell blastomeres both antigens aggregate in a single cluster and do so whether the surface phenotype of the blastomeres is polar or apolar. The position of this cluster is not consistently related to the point of contact with the other cell in the pair but there is a suggestion that in cells with a polar surface phenotype the polar foci of Golgi/lysosomal antigens are located between the nucleus and the surface pole at earlier time points, but shift to a position between the basolateral membrane and the nucleus at the later time point. In intact 16-cell embryos also, the aggregated Golgi/lysosomal antigens of polar cells appear to localize to the basal region. The distributions of these various organelles in embryonic cells reported here show a number of differences from those reported previously for mature, differentiated cells.

Animals↗
PubMed1985

DNA replication and compaction in the cleaving embryo of the mouse.

The effects of aphidicolin, a reversible inhibitor of DNA polymerase alpha, both on replication and on development of the mouse embryo from the 2- and 4-cell stages to the compacted late 8-cell stage have been assessed. The continuous presence of aphidicolin from G1 of the 4-cell stage resulted in inhibition of DNA replication and prevention of division from 4 to 8 cells, but was without effect on the timing or incidence of cell flattening, surface polarization and cytoplasmic polarization. The continuous presence of aphidicolin from G1 of the 2-cell stage resulted in inhibition of DNA replication, division, and polarization. Some slight intercellular flattening in a few embryos did occur. If addition of aphidicolin was delayed by 10 h to early in G2 of the 2-cell stage, further rounds of replication were blocked and some embryos failed to cleave to 4-cells. Nevertheless, almost all embryos showed evidence of flattening and polarization regardless of cell number. In contrast, if aphidicolin was added in G1 of the 2-cell stage and removed after 10 h, the cells showed delayed DNA replication, little evidence of division, and no cell flattening or polarization. We conclude that DNA replication at the 2-cell stage may be essential for the components of compaction studied, but that DNA replication at the 4- and 8-cell stages is not.

Animals↗
PubMed1985

Evaluation of pharmacy and therapeutics committee drug evaluation reports.

Pharmacy and therapeutics (P & T) committee drug evaluation reports prepared by pharmacies and drug information centers (DICs) and product package inserts were compared with standard guidelines to evaluate their quality. Letters were sent to 143 hospital pharmacies asking them to submit a previously prepared drug evaluation report on temazepam, moxalactam disodium, or atenolol. The reports and package inserts for these three drugs were evaluated by the presence of 40 elements derived from the published ASHP guidelines for drug evaluation report preparation. Responses were obtained from 124 (87%) pharmacies; however, only 80 reports (60 DIC-prepared and 20 pharmacy-prepared) were received. The reports contained a mean of 28 of the 40 (70%) possible elements. The most frequently omitted elements were AHFS number, potential unlabeled uses, drug-drug interactions, drug-disease-laboratory test interactions, risk and benefit data, prevention and treatment of side effects, comparisons with established treatment, and disadvantages of the drug under consideration. Although the reports prepared by the DICs and pharmacies contained the same amount of information, the DIC-prepared reports included data more frequently on supply sources, therapeutic indications, approved labeling, comparison with established treatment, bioavailability and pharmacokinetics, and recommendations. Most of the reports contained more elements than the corresponding package inserts. The product package inserts did not contain the comparative elements required for P & T committee decisions. Both the pharmacy- and DIC-prepared reports failed to contain all 40 elements recommended in the standard guidelines, suggesting the need for more thorough reports.

Atenolol↗
PubMed1985

Developmental variability within and between mouse expanding blastocysts and their ICMs.

We have attempted to reduce the developmental heterogeneity amongst populations of mouse blastocysts by synchronizing embryos to the first visible signs of blastocoel formation. Using embryos timed in this way, we have examined the extent of variation of inside and outside cell number and of inside cell size, nuclear DNA content and developmental potential, between and within embryos of a similar age postcavitation. The overall impression gained is one of wide heterogeneity in inside:outside cell number ratios and in cell cycling and its relation to cavitation among embryos of similar age postcavitation. However, the simplest explanation of our results suggests that cavitation generally begins at a time when most outside cells are in their sixth developmental cell cycle and that outside cells, as a population, are a little ahead of inside cells in their cell cycling. Additionally we present evidence that, within at least some individual inner cell masses (ICM), there is intraembryo variation in the time at which inside cell developmental potential becomes restricted.

Animals↗
PubMed1985

Meiosis II, mitosis I and the linking interphase: a study of the cytoskeleton in the fertilised mouse egg.

Data concerning the organisation and the role of microtubules and microfilaments during the 20 h following fertilisation in vitro of the mouse oocyte is reviewed. This period covers the fertilisation-induced completion of meiosis, from second meiotic metaphase through the first mitotic cell cycle, and involves the union of the haploid parental genomes. Various antibodies were used against actin, tubulin and PCM to describe the localisation of the cytoskeletal components and the two cytoskeleton-disrupting drugs nocodazole and CCD to assess the functional importance of the cytoskeleton.

Animals↗
PubMed1984

Structural and functional studies of hemoglobin Wayne: an elongated alpha-chain variant.

Hemoglobin Wayne (Hb Wayne) is a frame-shift, elongated alpha-chain variant that exists in two forms, with either asparagine or aspartic acid as residue 139. Oxygen equilibrium studies showed that stripped Hb Wayne Asn and Hb Wayne Asp possessed high oxygen affinity (P 1/2 = 0.60 and 0.23 mmHg at pH 7, respectively), were non-co-operative and have a markedly reduced Bohr effect (-delta log P 1/2/pH (7 to 8) = 0.34 and 0.10, respectively). Adding organic phosphate results in a decreased oxygen affinity and increased Bohr effect for both Hbs Wayne. The overall rate of carbon monoxide binding at pH 7 (l' = 5.6 X 10(6) M-1 S-1) was similar for both stripped Hbs Wayne and was 25-fold more rapid than that of stripped Hb A. When organic phosphate was added, Hb Wayne Asn exhibited a homogeneous slower rate of carbon monoxide binding (l' = 2.6 X 10(6) M-1 S-1), whereas Hb Wayne Asp showed heterogeneous binding (l' = 6.1 X 10(6) and 2.6 X 10(6) M-1 S-1 for fast and slow phases, respectively). The rates of overall oxygen dissociation and oxygen dissociation with carbon monoxide replacement for both Hbs Wayne were found to be slow compared to Hb A and uniquely different from each other. Similarly, sedimentation velocity experiments indicated that, although Hb Wayne Asn and Hb Wayne Asp were both less tetrameric than Hb A, each hemoglobin exhibited a distinct degree of oxygen-linked subunit dissociation. These observed differences in the allosteric properties of Hb Wayne Asn and Hb Wayne Asp appeared to be directly attributable to residue 139. The equilibrium and kinetic data are consistent with the X-ray diffraction analysis of Hb Wayne Asp, which shows that the C terminus of the deoxytetramers are severely disordered, a condition that results in major destabilization of the T conformation and disruption of normal hemoglobin function.

Amino Acid Sequence↗
PubMed1984

Intracerebral haemorrhage complicating dural arteriovenous fistula: a report of two cases.

Two patients presented with unilateral peri-orbital pain, proptosis, chemosis and external ophthalmoplegia. They were shown to have dural arteriovenous fistulae related to the cavernous sinus. Intracerebral haemorrhage occurred in both patients within 18 months of presentation; this gave rise to focal seizures and signs of unilateral hemisphere dysfunction. The haematomas were in the region drained by the superficial middle cerebral vein ipsilateral to the shunt and are presumed to have been the result of locally raised venous pressure.

Aged↗