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Biomedical subjects

T Yee

Publications and source records attributed to T Yee.

At least 19 recordsLinked to original sources
PubMed2000

Recurrent idiopathic lumbosacral plexopathy.

Recurrent idiopathic lumbosacral plexopathy has rarely been reported in the literature. The present report describes a 59-year-old man presenting with recurrent episodes of acute leg pain, followed by weakness. After each episode, symptoms progressed for several months before peaking. Thereafter, gradual recovery ensued. Electrodiagnostic studies revealed primarily a patchy pattern of denervation in the distribution of part of the lumbosacral plexus, sparing the paraspinal muscles. Extensive evaluations for an underlying cause were unrevealing. Thus, these episodes are suggestive of recurrent idiopathic lumbosacral plexopathy, and the present case is compared with previous cases reported in the literature.

Denervation↗
PubMed1997

Regional variation in the incidence of hip fracture in New Zealand.

AIM: To determine the regional incidence of hip fracture among individuals aged 60 years or older in New Zealand. METHODS: New Zealand Health Information Service inpatient morbidity data for the years 1988-92 were examined by area health board region to identify all hip fractures (ICD N820) among individuals aged 60 years or older. RESULTS: Substantial regional variation exists in the incidence of hip fractures among older people in New Zealand. Among both men and women, similar regional variations were observed with the age-standardised rates being consistently highest in the West Coast (790 per 100,000 for women and 360 per 100,000 in men) and lowest in Northland (540 per 100,000 in women and 185 per 100,000 in men). CONCLUSION: These findings have implications for resource allocation, both in terms of targeting prevention initiatives and in providing acute and long term management of hip fracture patients. In addition, they raise questions as to why such variations in hip fracture incidence exist in New Zealand.

Aged↗
PubMed1995

Hospital admissions and deaths due to congestive heart failure in New Zealand, 1988-91.

AIMS: Congestive heart failure is believed to be a major public health problem in most Western countries; however, little is known about the extent of morbidity and mortality from congestive heart failure in New Zealand. This paper reports data on hospital admissions and mortality due to congestive heart failure in New Zealand during the years 1988-91. METHODS: All data were obtained from the New Zealand Health Information Service. Deaths from congestive heart failure were identified from ICD-9 codes indicating a primary diagnosis of congestive heart failure. Hospitalisations for congestive heart failure were identified both from ICD-9 codes indicating a primary diagnosis of congestive heart failure and from codes indicating a diagnosis of congestive heart failure secondary to chronic rheumatic heart disease, ischaemic heart disease or valvular heart disease (nonrheumatic). RESULTS: Each year there was an average of about 850 deaths ascribed to heart failure; two-thirds of these occurred in patients over the age of 75 years. Each year there was also an average of about 8000 hospital admissions of about 5000 patients for congestive heart failure; 75% of these admissions involved patients over 65 years old. The mean duration of hospital stay for congestive heart failure was 16 days. On this basis, it is estimated that hospital admissions for congestive heart failure are likely to cost about NZ$50 million each year, or about 1% of the total health budget. CONCLUSIONS: Congestive heart failure is clearly a major public health problem in New Zealand with high hospitalisation and mortality rates. Several strategies have been proven to reduce mortality and hospital admissions for congestive heart failure and these should be utilised widely in patients at risk.

Aged↗
PubMed1994

CT findings of hypoxic basal ganglia damage.

The outcome of hypoxic ischemic injury ranges from complete recovery to a persistent vegetative state or death, depending on the length of time the patient remains unconscious and the degree of associated cardiac failure. We describe three patients who were comatose from a hypoxic and/or ischemic injury and whose principal computed tomographic (CT) finding was bilateral basal ganglia hypodensities. Two of these patients were discharged from the hospital with minimal residual neurologic deficits. These cases and review of the literature suggest that ischemic basal ganglia signs on CT scan are not necessarily a predictor of severe neurologic sequelae.

Adult↗
PubMed1993

Laser iridoplasty in the treatment of severe acute angle closure glaucoma.

Twenty eyes of 19 patients presenting with acute angle closure glaucoma (AACG) which failed to respond to medical treatment were treated with laser iridoplasty. In all 20 eyes, laser peripheral iridectomy (PI) was prevented by a hazy cornea. In all cases, iridoplasty resulted in a rapid and significant reduction in intraocular pressure. Laser iridoplasty appears to have a useful role in the management of medically unresponsive AACG, particularly in those cases where laser peripheral iridotomy (PI) has failed or is not possible to perform.

Acute Disease↗
PubMed1991

Lipid and membrane fluidity abnormalities in platelets and megakaryocytes of the hereditary macrothrombocytopenic Wistar Furth rat.

Biochemical and functional abnormalities of megakaryocytes and platelets were studied in Wistar Furth (WF) rats which have genetically determined macrothrombocytopenia and megakaryocytopenia, and were compared with their counterparts in Sprague-Dawley (SD) rats. Both megakaryocytes and platelets synthesized phospholipids from [14C]acetate. WF and SD megakaryocytes incorporated 0.27 and 0.29 nmol acetate per 10(6) cells, respectively. Phosphatidylcholine (PC) accounted for 64% and 58% of the PL radioactive label in megakaryocytes of SD and WF rats, respectively, (P less than 0.05), while 69% of labeled activity was associated with PC of SD platelets compared to 60% found in PC of WF platelets (P less than 0.01). In WF platelets a significant increase in the levels of lysophosphatidylcholine (6.1% vs. 3.0%) was observed. WF platelets had substantially higher levels of esterified cholesterol, triglycerides, ceramides and a 3-fold increase in the total protein per platelet compared to SD platelets. The fatty acid composition of WF platelet PC showed quantitative abnormalities. Plasma lecithin-cholesterol acyl transferase activity and platelet function monitored by the uptake and release of [14C] serotonin showed nonsignificant variations between SD and WF rats. Compared with the control, platelet membrane fluidity, measured by fluorescence polarization using platelets labeled with 1,6-diphenyl-1,3,5-hexatriene, was significantly decreased in the WF rats.

Animals↗
PubMed1991

Early events in the synthesis of the multicopy single-stranded DNA-RNA branched copolymer of Myxococcus xanthus.

Myxobacteria and a variety of strains of Escherichia coli contain an unusual extrachromosomal element, a small single-stranded branched copolymer of DNA and RNA (msDNA). Interest in msDNA stems from the presence of a 2'-5' linkage between its DNA and RNA moieties and the possible involvement of reverse transcriptase in its synthesis. Two groups have proposed a model for the synthesis of msDNA that involves the following sequence of events: 1) synthesis of an RNA precursor; 2) addition of a dNTP in a 2'-5' linkage to the RNA precursor (branch priming); 3) synthesis by reverse transcriptase of complementary DNA on the primed RNA precursor; 4) concomitant processing of the RNA precursor by RNase H; and 5) further processing of the RNA precursor by RNase H; and 5) further processing of the branched polymer. The branch priming hypothesis (step 2) was originally based on pulse-chase experiments using a lengthy pulse of 30-min duration. Our experiments with shorter pulse durations demonstrate a variety of intermediate forms not predicted by this model. Specifically, we find that early in synthesis, intermediate msDNA forms appear that are apparently not branch-linked to corresponding RNA moieties. The concomitant RNase H hypothesis (step 4) was based in part on intermediate trapping experiments using dideoxy NTPs to interrupt msDNA synthesis. These experiments showed an apparent complementary relationship between DNA length and RNA length in the trapped forms. In contrast, our experiments show that DNA elongation and RNA processing follow different kinetics. These results suggest an alternate model for synthesis of msDNA in which a conventionally primed DNA moiety is joined with the RNA moiety in a branch ligation event taking place several minutes after the synthesis of both moieties.

Bacteria, Aerobic↗
PubMed1991

Autogeneic bone marrow and porous biphasic calcium phosphate ceramic for segmental bone defects in the canine ulna.

The purpose of this study was to evaluate a porous biphasic hydroxyapatite-calcium phosphate ceramic as a modifier and extender of an autogeneic marrow graft for filling a 2.5-cm segmental bony defect. Twenty adult mongrel dogs were surgically treated to create diaphyseal defects in the left ulnae. The defects were (1) filled with autogeneic bone marrow mixed with granular hydroxyapatite-tricalcium phosphate ceramic (granular ceramic); (2) grafted with a solid block of ceramic soaked in autogeneic bone marrow (block ceramic); (3) received no graft (no implant); or (4) were grafted with autogeneic bone marrow alone (bone marrow). All animals were followed clinically and roentgenographically for 24 weeks and then killed. Repair of diaphyseal defects with the block ceramic led to three solid unions and three fibrous unions; with the granular ceramic implants and marrow, the defects of five dogs formed solid unions, and one progressed to a fibrous union. Defects in all five dogs grafted with autogeneic bone marrow united. The three dogs with no implant formed nonunions. Histology showed normal marrow and only a light immune reaction. Complete bridging of the defect in the dogs treated with the granular ceramic occurred significantly earlier than bridging in the dogs grafted with bone marrow alone. Histomorphometry, performed on the block ceramic implants indicated active resorption of ceramic. Clinically, addition of ceramic to a marrow graft improved the handling characteristics of the graft material and accelerated healing according to roentgenographic evaluation.

Animals↗
PubMed1991

Image processing software for enhanced visualization of faint or noisy autoradiographic images.

A computer program for digital image processing is described which can be implemented using scanning densitometer hardware pre-existing in most biology departments plus computer video hardware which may either pre-exist in the biology department or would represent a moderate upgrade over an already planned computer purchase. The primary purpose of this computer program is to provide contrast enhancement of faint or low contrast autoradiograph images and to implement background subtraction and digital smoothing methods which permit visualization of blurry electrophoresis bands against noisy backgrounds. However, the program also has modest editing capabilities that allow its use in the routine preparation of images for publication. Finally, the program has facilities for deblurring, edge enhancement and multiple image averaging, which give it usefulness in other forms of photographic analysis.

Autoradiography↗
PubMed1990

Biochemical and functional abnormalities in hypercholesterolemic rabbit platelets.

This study was designed to elucidate changes in rabbit platelet lipids induced by a cholesterol rich diet and to explore the possible correlation of these lipid changes with platelet abnormalities. Pronounced biochemical alterations were observed when serum cholesterol levels of 700-1000 mg% were reached. Hypercholesterolemic (HC) platelets contained 37% more neutral lipids and 16% less phospholipids than the controls. Lysolecithin, cholesterol esters and phosphatidylinositol (PI) levels were increased in HC platelets, and the levels of phosphatidylcholine (PC) were decreased. The cholesterol/phospholipid molar ratio of lipidemic platelets increased from 0.55 +/- 0.011 to 0.89 +/- 0.016 (P less than 0.01) in eight weeks. HC platelets had 90% more arachidonic acid (AA) in the PI than normal platelets. No significant changes in AA of PC were observed. Platelet function was monitored by the uptake and release of [14C]serotonin in platelet rich plasma (PRP), using varying concentrations of collagen as an aggregating agent. The uptake of [14C]serotonin in HC and normal platelets ranged from 78-94%. The percent of [14C]serotonin released from normal and HC platelets was proportional to the concentration of collagen. However, lipidemic platelets were hyperreactive to low concentrations of collagen. Incorporation of 50 microM acetylsalicylic acid into the aggregating medium suppressed the release of [14C]serotonin in normal PRP by more than 90%, but had only a partial effect on lipidemic PRP.

Animals↗
PubMed1990

Collagenase production by guinea pig megakaryocytes in vitro.

Cultured guinea pig bone marrow megakaryocytes were found to secrete a 92-kd collagenase that was detected by digestion of gelatin in a polyacrylamide substrate gel assay. Neither casein or bovine serum albumin were digested by this enzyme. The enzyme is a neutral metalloprotease. Its secretion is increased by thrombin (1.0 U/ml) and phorbol myristate acetate (10 ng/ml) and is unaffected by prostaglandin E1 (10 microM). In the absence of serum, gelatinase secretion is inhibited, but it can be stimulated by cytochalasin D (1.0 microgram/ml). Gelatinase activity in the medium from megakaryocytes cultured on rat tail collagen gel is decreased. Medium from megakaryocytes cultured on Matrigel contains a second gelatinase of 90 kd. Addition of the tetrapeptide RGDS to the cultures on Matrigel blocks the appearance of the 90-kd gelatinase. Platelets contained both a 92- and a 90-kd gelatinase that was detected only after thrombin activation. The results indicate that megakaryocytes can secrete a collagenase, and its secretion may be in part controlled by interaction with the extracellular matrix. The appearance of the 90-kd gelatinase may be associated with megakaryocyte maturation and platelet formation.

Animals↗
PubMed1989

Megakaryocytopenia in W/Wv mice is accompanied by an increase in size within ploidy groups and acceleration of maturation.

Megakaryocytopoiesis was evaluated in W/Wv mice and their normal +/+ littermates to analyze the mechanisms by which normal platelet production is maintained in W/Wv mice even though numbers of megakaryocytes are low. Relative sizes of megakaryocytes, and their nuclei and cytoplasm, were measured microscopically in bone marrow smears, and the ploidy of the same cells was measured by two-wavelength microspectrophotometry. Maturation rate of megakaryocytes was estimated after they were labeled with tritiated thymidine. W/Wv megakaryocytes were macrocytic: average cell size was increased in each ploidy group. The increase in cytoplasmic area exceeded that of the nucleus. Further analysis of the predominant 16N ploidy group revealed that the increase in average cell size was due to depletion of cells of small size. Megakaryocytes matured more rapidly than normal in W/Wv mice. These results showed that megakaryocyte size and ploidy can be regulated separately. They suggest that alterations in cell growth and maturation may be mechanisms by which the organism can compensate for a deficiency in numbers of megakaryocytes, but they do not define the mechanism by which the deficiency may be sensed or by which the compensatory changes may be mediated. This is a US government work. There are no restrictions on its use.

Animals↗
PubMed1989

5-fluorouracil-induced thrombocytosis in mice is independent of the spleen and can be partially reproduced by repeated doses of cytosine arabinoside.

Experiments were done to characterize the pronounced and prolonged thrombocytosis that develops in mice during recovery from the marrow hypoplastic effects of a single injection of 5-fluorouracil (5-FU). Measurements were made of platelet and megakaryocyte numbers, size of mature megakaryocytes, marrow cellularity, hematocrit, and reticulocytes. Mice that had been splenectomized a month before receiving 5-FU displayed the same pattern of thrombocytosis as intact mice, so a role for the spleen in its genesis or persistence could not be identified. During recovery from two or three doses of cytosine arabinoside (Ara-C), given at intervals of 2 days, thrombocytosis and megakaryocytosis of similar magnitudes to those seen after 5-FU occurred. Bone marrow cellularity, hematocrits, and reticulocytes were identical after three doses of Ara-C or one dose of 5-FU. Megakaryocytes were initially macrocytic during recovery from the hypoplastic thrombocytopenia produced by 5-FU or Ara-C. These similarities to effects of repeated doses of Ara-C suggested that some of the effects of 5-FU were due to its prolonged action in vivo, which could cause sequential killing of proliferating cells. Abnormalities of megakaryocytes and platelets reversed promptly when normal or increased numbers of megakaryocytes and/or platelets were produced after Ara-C, but they persisted in mice that received 5-FU. This difference suggested that regulation of megakaryocyte progenitors was perturbed during recovery from 5-FU.

Animals↗
PubMed1988

Morphological and kinetic abnormalities of platelets in hypercholesterolemic rabbits.

Hypercholesterolemia (HC = hypercholesterolemia or hypercholesterolemic) was produced in rabbits by feeding them diets supplemented with cholesterol and peanut oil. Platelet counts and volumes, white cell counts, reticulocyte counts, and hematocrits were determined at intervals for 8-12 weeks in blood from HC animals and controls on a normal rabbit diet. Microthrombocytosis was a consistent occurrence in the presence of HC, developing as early as 2 weeks into the diet. Microthrombocytosis was generally associated with normal platelet counts, but mild thrombocytosis occurred late in the diet at the time of the highest levels of serum cholesterol (greater than 1300 mg/dl). Platelets from HC rabbits were morphologically normal by transmission electron microscopy. Survivals of 51Cr-labeled platelets from HC and non-HC rabbits were measured in HC and non-HC recipients. The results identified an intrinsic defect in the ability of HC platelets to survive in the circulation. They also confirmed previous findings of an environmental defect in HC that causes shortened platelet survival.

Animals↗
PubMed1988

Megakaryocytes increase in size within ploidy groups in response to the stimulus of thrombocytopenia.

Experiments were done to determine if sizes of megakaryocytes within a defined maturation stage were strictly determined by amount of nuclear DNA. Normal mice, mice recovering from an acute episode of thrombocytopenia induced by a single injection of heterologous antiplatelet serum (APS), and mice with sustained thrombocytopenia from daily injections of APS were examined. Areas of mature megakaryocytes were measured in bone marrow smears stained with polychromatic stains. The nuclear DNA content of the same cells was then measured microspectrophotometrically after staining by the Feulgen reaction. Normal megakaryocytes showed a trimodal, lognormal distribution of nuclear chromophore, corresponding to 8n, 16n, and 32n with smaller numbers of 4n and 64n cells; 16n was the predominant ploidy class. In response to thrombocytopenia, ploidy values shifted: the proportions of 8n and 16n cells decreased; 32n and 64n cells increased; 128n megakaryocytes occasionally appeared. These shifts were accompanied by an increase in the average size of all megakaryocytes. In addition to shifts to higher ploidy values, megakaryocytes within ploidy groups became larger than normal megakaryocytes of the same ploidy especially in the mice with sustained thrombocytopenia. These findings show that megakaryocyte size in thrombocytopenic mice is influenced by factors other than the ploidy and maturity of the cell.

Anemia↗
PubMed1987

Thrombocytopoietic response to immunothrombocytopenia in nude mice.

Thrombocytopoiesis was evaluated in T cell-deficient nu/nu mice and in T cell-replete nu/+ controls to determine if abnormalities would be associated with the deficiency of T cells. Mice were studied in the unperturbed steady state and after acute immunothrombocytopenia was induced by an injection of guinea pig antimouse platelet serum (APS). The state of thrombocytopoiesis was determined from platelet counts, megakaryocyte size, megakaryocyte number, and numbers of Meg-CFC. Splenic lymphocytes were evaluated by response to the mitogens bacterial lipopolysaccharide (LPS), phytohemagglutinin (PHA), and concanavalin A (Con A). Hematocrits, reticulocyte counts, leukocyte counts, marrow cellularity, GM-CFC, and BFU-E also were measured. Steady state thrombocytopoiesis was identical in nu/nu and nu/+ mice. In response to an injection of APS, acute thrombocytopenia was followed by macromegakaryocytosis and rebound thrombocytosis in mice of both genotypes. Splenic Meg-CFC increased in nude mice after APS or an injection of normal guinea pig serum (NGpS), and splenic GM-CFC increased after APS. Neither Meg-CFC nor GM-CFC increased in the spleens of nu/+ mice, but they showed early transient increases in bone marrow that did not occur in nu/nu mice. Sporadic, but weak, mitogenic responses to PHA or Con A were occasionally observed with nu/nu spleen cells, but these did not correlate with the state of thrombocytopoiesis. The results demonstrated that platelet production was normal in nu/nu mice and that megakaryocytopoiesis and platelet production responded to the stimulus imposed by acute immunothrombocytopenia. Increases in megakaryocyte size and platelet production occurred independently of changes in numbers of Meg-CFC, GM-CFC, or BFU-E. A normal complement of T cells appears to be unnecessary for normal platelet production and its augmentation in response to the stimulus of acute immunothrombocytopenia in vivo.

Animals↗
PubMed1986

Postirradiation thrombocytopoiesis: suppression, recovery, compensatory states, and macromegakaryocytosis.

Two unusual features of the regulation of megakaryocytopoiesis have been found in irradiated mice. The first is that the response to thrombocytopenia loses its specificity for thrombocytopoiesis when the thrombocytopenia is induced at the time of exposure to sublethal doses of radiation. Under these conditions, there is stimulation of both thrombocytopoiesis and erythropoiesis. The second unusual feature is that a completely or partially compensated hypomegakaryocytic state may develop after "recovery" from the earlier severe postirradiation myelodepression. Occurrence of this condition is not dependent on the presence or absence of the spleen. It is characterized by a dissociation between platelet and megakaryocyte numbers, with platelets being relatively higher. There is an associated increase in mean megakaryocyte size. Both the megakaryocytopenia and macromegakaryocytosis are due to a deficiency of smaller megakaryocytes in the marrow. The postirradiation abnormality of megakaryocyte size distribution can not be accounted for by irradiation-induced abnormalities of either hemopoietic or stromal cells. The degree of megakaryocytic macrocytosis does not correlate with the platelet or megakaryocyte count after recovery from sublethal irradiation or after recovery from lethal irradiation and rescue with normal bone marrow cells. Megakaryocytic macrocytosis, as identified by an increase in average size of mature cells, occurs in response to thrombocytopenia and in several hypomegakaryocytic states in which thrombocytopenia is absent or is mild in degree. Comparison of size distribution curves, analysis of sizes of immature megakaryocytes, and determination of the stability of the megakaryocyte count indicate that different mechanisms probably prevail. The presence or absence of thrombopoietin or other megakaryocyte growth factors in these conditions may provide clues about the mechanisms.

Animals↗