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Biomedical subjects

P Gregory

Publications and source records attributed to P Gregory.

At least 73 records · Page 4Linked to original sources
PubMed1986

Changes in skeletal-muscle myosin isoenzymes with hypertrophy and exercise.

The patterns of myosin isoenzymes in fast- and slow-twitch muscles of the rat hindlimb were studied, by pyrophosphate/polyacrylamide-gel electrophoresis, with hypertrophy (induced by synergist removal) and with spontaneous running exercise of 4 and 11 weeks duration. At 11 weeks, changes with hypertrophy in the slow-twitch soleus, composed of greater than 95% SM2 (slow myosin 2) in normal muscles, were minor, and consisted of an increase in the SM1 and SM1', and a loss of intermediate myosin (IM), an isoenzyme characteristic of Type IIa fibres [Fitzsimons & Hoh (1983) J. Physiol. (London) 343, 539-550]. The changes were dramatic, however, in the fast-twitch plantaris muscle. There was a 3-fold increase in the proportion of SM. In addition, IM became the predominant isoenzyme in the profile of hypertrophied plantaris by 4 weeks. These increases were balanced by decreases in the proportion of FM2 (fast myosin 2), with FM1 completely absent from the profile at 11 weeks. The changes in the plantaris with exercise were similar in direction but not as extensive as those with hypertrophy, and FM1 remained present at control levels throughout the study. When hypertrophy and exercise were combined, the increase in slow myosin was equal to the sum of the increases with each treatment alone. Changes at 4 weeks were intermediate between those of control and 11-week muscles. Peptide mapping of individual myosin isoenzymes showed that the heavy chains of IM were different from either fast or slow heavy chains. Furthermore, IM was found to be composed of a mixture of fast and slow light chains. These changes suggest that a transformation of myosin from fast to slow isoforms was in progress in the plantaris in response to hypertrophy, via a Type-IIa-myosin (IM) intermediate stage, a phenomenon similar to that occurring in chronically stimulated fast muscles during fast-to-slow transformation [Brown, Salmons & Whalen (1983) J. Biol. Chem. 258, 14686-14692].

Adenosine Triphosphatases↗
PubMed1986

Cell surface involvement in cancer metastasis: an NMR study.

NMR spectroscopy is one of the few techniques which has the sensitivity to detect subtle changes to the surface chemistry of cells. It has previously been demonstrated that high resolution 1H NMR methods can distinguish tumour cells with the capacity to metastasis and this information appears to arise from a type of proteolipid in or attached to the plasma membrane. Here we report that the 1H NMR signal, which we have used to identify metastatic cells in rat tumours, is significantly reduced in intensity after cultured cells are treated with trypsin/EDTA. The long T2 relaxation value (greater than 350 ms) observed in metastatic cells is absent after enzyme treatment. 2D scalar correlated NMR (COSY) spectra of these treated cells show that a cross peak normally associated with malignancy and metastatic disease is markedly reduced. These findings indicate that the plasma membrane lipid particle which generates the high resolution spectrum is directly affected by trypsin/EDTA. Alterations to the cell surface properties were also demonstrated in vivo since reduced numbers of metastases were observed in animals injected with enzyme-treated cells. The correlation between the absence of a long T2 relaxation value and the diminished numbers of metastases in animals suggests that the plasma membrane particle is involved in the metastatic PROCESS.

Adenocarcinoma↗
PubMed1986

Alterations in the X chromosome replication pattern induced by 5-azacytidine in a human tumor line.

Biochemical studies have shown that the cytosine analog, 5-azacytidine (5-azaC), induces hypomethylation and reactivates specific X-linked genes. Cytogenetically, it has been shown that this hypomethylating agent alters the replication pattern of the late-replicating, inactive X chromosome. In order to analyze the effect of 5-azaC on the X chromosome replication pattern of tumor cells with multiple X chromosomes, 5-azaC treatment, followed by terminal bromodeoxyuridine (BrdU) pulses, was applied to the human breast tumor cell line ZR-75-30. Metaphase spreads were analyzed for the presence of X chromosomes with altered replication banding patterns. Seventy-four percent of the untreated cells contained at least one typical, pale-staining, inactive X chromosome as compared to only 8% of the cells in the treated groups. This demonstrates a dramatic change in the replication pattern of the inactive X chromosome of these neoplastic cells in response to 5-azaC treatment. These results suggest that neoplastic tissue is highly responsive to this hypomethylating agent, which may be related to the high degree of DNA hypomethylation observed in neoplasias.

Azacitidine↗
PubMed1986

A monoclonal anti-neuroblastoma antibody that discriminates between human nonhematopoietic and hematopoietic cell types.

A murine IgG2a monoclonal antibody, termed 6-19, was characterized in terms of its ability to bind to human cell lines and tissues. The hybridoma was selected for antibody binding to multiple human neuroblastoma cultured cell lines but not to peripheral blood mononuclear cells. 6-19 binds to the cell surface of all cultured human nonhematopoietic tumor cell lines tested, to cultured human fibroblasts and endothelial cells, and to nonhematopoietic tumors of many types. It does not bind detectably to any hematopoietic cells, leukemia cells, or lymphomas. In the presence of complement, 6-19 is very cytotoxic to cultured human neuroblastoma cells but not to bone marrow granulocyte-macrophage colony-forming cells. The 6-19 monoclonal antibody may prove useful in the identification or destruction of tumor and stromal cells in bone marrow.

Animals↗
PubMed1986

Bladder cancer xenografts: a model of tumor cell heterogeneity.

Twenty bladder biopsies from patients with primary transitional cell carcinoma were inoculated into nude mice. To date, eleven of these have grown as primary implants and three serially transplantable xenograft lines (UCRU-BL-12, UCRU-BL-13, UCRU-BL-14) have been established. The histological and ultrastructural features of human transitional cell carcinoma have been maintained in each line. Despite a relatively uniform histological appearance, several indices of occult tumor heterogeneity have been revealed. Immunocytochemical staining was negative for beta-subunit human chorionic gonadotrophin but positive for carcinoembryonic antigen only in areas of squamous differentiation. All three tumors bound peanut lectin. Flow cytometric DNA analysis of UCRU-BL-13 showed multiple aneuploid peaks, separate populations being demonstrated in different xenografts of the same generation. However, the morphologies of these tumors remained identical. On initial implantation UCRU-BL-12 and UCRU-BL-14 were near diploid but aneuploid populations became apparent with increasing passage number. Each xenograft line caused cachexia in the host mice. Treatment with the cisplatin analogue, isopropyl platinum, ameliorated the cachexia displayed by mice carrying UCRU-BL-14 but did not cause tumor regression. UCRU-BL-12, when tested with cisplatin, isopropyl platinum, and carboplatin, showed equivalent growth retardation with each drug. These xenografted human bladder cancers may be useful models for the study of heterogeneity of the tumor populations in bladder cancer and for the evaluation of new approaches to treatment.

Adult↗
PubMed1985

Alterations in the time of X chromosome replication induced by 5-azacytidine in a patient with 48,XXXY/47,XXY.

It has recently been shown that 5-azacytidine (5-azaC) can induce altered replication patterns of the late-replicating X chromosome in normal female cells. This has been demonstrated by bromodeoxyuridine labelling of cells late in the S phase. In the present study the same method was applied to the lymphocytes of a Klinefelter patient (48,XXXY/47,XXY). Significant 5-azaC-induced changes in the replication of the entire inactive X chromosome, from late to early, were found in the lymphocytes of this patient. These results indicate that hypomethylating agents can not only alter the replication of individual bands, but also change the gross replication schedule of multiple inactive X chromosomes in the presence of a Y chromosome.

Azacitidine↗
PubMed1984

High-resolution proton nuclear magnetic resonance analysis of metastatic cancer cells.

High-resolution proton nuclear magnetic resonance (NMR) studies of intact cancer cells revealed differences between cells with the capacity to metastasize and those that produce locally invasive tumors. The NMR resonances that characterize the metastatic cells were associated with an increased ratio of cholesterol to phospholipid and an increased amount of plasma membrane-bound cholesterol ester. High-resolution NMR spectroscopy could therefore be used to assess the metastatic potential of primary tumors.

Animals↗
PubMed1984

Passive avoidance in rats: disruption by dopamine applied to the nucleus accumbens.

The acquisition of a one-trial step-through passive avoidance task was examined in rats following the administration of nialamide IP and dopamine (DA) or saline into the nucleus accumbens. DA-treated rats displayed impaired learning of the task as evidenced by their lower step-through latencies on a retest trial 7 days later. The specificity of this impairment was studied in a 2 x 2 design involving intracerebral injections prior to both training and testing trials. It was found that DA treatment prior to the training trial disrupted learning or memorization of the task but that DA did not affect performance or retrieval and did not induce state-dependent learning. These findings suggest that DA applied to the nucleus accumbens does not facilitate learning per se.

Animals↗
PubMed1984

Dopamine applied into the nucleus accumbens and discriminative avoidance in rats.

The actions of dopamine (DA) administered into the nucleus accumbens on motor function and discrimination were examined in rats trained to perform a discriminative conditioned avoidance response (DCAR). alpha-Methyl-p-tyrosine was found to suppress performance of the CAR although it did not impair discrimination. The administration of DA reinstated CAR performance but it also increased discriminative errors. Multivariate comparisons suggested that both of these effects were closely related to the stimulation of intertrial crossings by DA.

Animals↗
PubMed1984

Characterization of the biophysical properties of human tumor and bone marrow cells as a preliminary step to the use of centrifugal elutriation in autologous bone marrow transplantation.

The principle of centrifugal elutriation (CE) depends on a balance of an outwardly directed centrifugal force and inwardly directed fluid flow and buoyant forces. This method (CE) can be used effectively to separate cells on the basis of size. In the murine model, neoplastic cells from different tumors are generally larger than bone marrow cells and can be removed from bone marrow almost completely with centrifugal elutriation. In order to determine if CE is capable of eliminating human tumor cells from harvested bone marrow (BM), the biophysical characteristics of a variety of human tumor cells and bone marrow cells were determined. Human tumor cells were dispersed into single cell suspensions by several enzymatic digestion and mechanical dissociation methods. The size and density characteristics of these cells were determined with an electronic particle counter and channelyzer and density gradients. Of 40 solid tumors studied, 29 tumors had cell size distributions distinctively larger than BM, as was found in the experimental animal model. The cell size distributions of tumor cells from 11 solid tumors and 7 leukemias were not substantially different from that of BM. Mixtures of BM and cultured human hypernephroma, ovarian, and neuroblastoma cells, were separated into BM and tumor fractions by CE. The separation results as indicated by the labeling index and colony forming efficiency of tumor cells in each fraction showed that a BM fraction virtually free of tumor cells could be obtained. Thus, CE should be able to separate BM cells from most tumor cells metastatic to BM.

Bone Marrow↗
PubMed1983

Chronic L-dopa treatment of rats and mice does not change the sensitivity of post-synaptic dopamine receptors.

The effects of L-Dopa + benserazide (L-Dopa + B) treatment on pre- and postsynaptic dopamine (DA) receptors were studied. Mice treated once daily P.O. with L-Dopa (200 mg/kg) + B (50 mg/kg) or vehicle for 10 days were used on the 11th day. After premedication with reserpine and alpha-methyltyrosine (alpha-MT), apomorphine (0.5-2.0 mg/kg) produced locomotor stimulation which was of equal intensity in the 3 treatment groups, even when the treatment dose of L-Dopa was increased to 400 mg/kg per day. In contrast, low doses of apomorphine (0.1-0.5 mg/kg) produced locomotor depression in B- and vehicle-treated mice but not in L-Dopa + B-treated mice. In rats treated I.P. twice daily with L-Dopa (200 mg/kg) + B (50 mg/kg), B (50 mg/kg) or vehicle for 12 days, apomorphine produced an equivalent degree of stereotypy on the 13th day in each of the 3 treatment groups. There were no treatment group differences in the binding of [3H]-spiperone or [3H]-leu-enkephalin to rat striatal membranes. The data suggest that long-term L-Dopa + B treatment of mice and rats does not change the sensitivity of postsynaptic DA receptors but may affect the sensitivity of DA autoreceptors.

Animals↗
PubMed1982

alpha-methyl-p-tyrosine inhibition of a conditioned avoidance response: reversal by dopamine applied to the nucleus accumbens.

These experiments sought to determine whether dopamine (DA) could reverse the depressive effects of alpha-methyl-p-tyrosine (AMPT) on a conditioned avoidance response (CAR). Rats were randomly allocated to shocked groups (CAR-trained) and non-shocked (CAR-naive) groups. The CAR-trained rats, conditioned to avoid an electric shock, were administered AMPT (150 mg/kg at -24 h and 50 mg/kg at -1 h, both IP), nialamide (80 mg/kg IP at -1 h) and saline (1 microliter) or DA (5 or 10 micrograms/microliters, dissolved in 1 microliter saline, at time 0) directly into the nucleus accumbens. The rats were then tested for CAR at 0.5, 1, 2, 3, 4, 8, 12, 24 an 48 h. The CAR-naive rats, conditioned to the behavioural environment without electric shock being presented, were administered AMPT, nialamide and DA or saline as above. Both doses of DA antagonised the AMPT-induced suppression of the CAR in the CAR-trained rats, reaching a maximum 2-4 h after its local application. In the CAR-naive rats, DA produced a "pseudo-CAR' that lasted about 4 h, but which completely disappeared at 8 h when the DA effect had worn off. These CAR-naive rats did not learn a CAR under the influence of DA. In a third group of rats, DA produced locomotor activation which, in its time course, resembled the effect of DA on CAR. It is concluded that the ability of DA to antagonise AMPT-induced depression of CAR is, in all likelihood, dependent upon DA-induced locomotor excitation, rather than upon an effect of DA on associative learning.

Animals↗
PubMed1981

CO2 responses of the cerebral circulation during drug-induced hypotension in the cat.

Concern has often been expressed that hypocapnia produced by controlled hyperventilation might further reduce cerebral perfusion during drug-induced hypotension. In the present studies, hypotension was induced in cats with either practolol/trimetaphan (five experiments) or practolol/nitroprusside (five experiments) together with controlled haemorrhage. Arterial PCO2 was altered between 17 and 51 mm Hg by varying inspired CO2 during constant-volume ventilation, first during control conditions of light halothane/nitrous oxide anaesthesia and then during hypotension to mean blood pressure of 36-37 mm Hg. Cerebral cortical perfusion was measured by the krypton clearance technique and pial artery diameter by the image-splitting method. Cerebral cortical blood flow did not alter with PaCO2 changes during trimetaphan hypotension, but some responsiveness to CO2 persisted during nitroprusside hypotension, though at less than half control levels. No changes in pial artery diameter were seen with CO2 during hypotension under either technique. It is postulated that CO2 responsiveness persisted with nitroprusside because cerebral blood flow (CBF) values were higher when hypotension was produced with this drug, as compared with trimetaphan. It would appear that hypocapnia does not further reduce CBF during trimetaphan hypotension but does do so with nitroprusside. However, the combination of hypocapnia and nitroprusside hypotension did not in any instance lower CBF below the values found during trimetaphan hypotension.

Animals↗
PubMed1981

Genetic labeling of an Ent plasmid that encodes heat-stable enterotoxin of enterotoxigenic Escherichia coli isolated from patients.

Ent plasmids of enterotoxigenic Escherichia coli that encode heat-stable enterotoxin (ST) and both ST and heat-labile enterotoxin (LT) were labeled with a kanamycin- and an ampicillin-resistance transposon, respectively. These transposons were kept stably in the respective Ent plasmids. By monitoring antibiotic resistance we could easily select strains carrying Ent plasmids. Strains carrying the labeled plasmids produced enterotoxins that were immunologically indistinguishable from those produced by the parent strains. Moreover the strain carrying a labeled ST-Ent plasmid produced 16 times more ST than the parent strain.

Ampicillin↗
PubMed1980

Loss of Sensitivity to Helminthosporium maydis Race T Toxin during Aging of Mitochondria Isolated from Texas Cytoplasm Corn.

Helminthosporium maydis Race T toxin caused the expected changes in freshly isolated mitochondria from T cytoplasm corn, namely complete uncoupling of oxidative phosphorylation, pronounced stimulation of succinate and NADH respiration, complete inhibition of malate respiration, and increased mitochondrial swelling. In contrast, identical toxin treatments of the mitochondria after 12 hours aging on ice resulted in partial uncoupling, much lower stimulation of succinate and NADH respiration, no inhibition of malate respiration, and no mitochondrial swelling. Almost all of the toxin sensitivity was lost by 6 hours aging. At this stage, the mitochondria were 208x and 66x less sensitive to toxin-induced changes in coupling of malate respiration and state 4 malate respiration rates, respectively. Loss of toxin sensitivity did not occur when the mitochondria were aged under nitrogen or in the presence of 5 millimolar dithiothreitol. This suggested that the aging effect was due to oxidation, possibly of sulfhydryl groups in one or more mitochondrial membrane proteins.

Journal Article↗
PubMed1980

Effects of Purified Helminthosporium maydis Race T Toxin on the Structure and Function of Corn Mitochondria and Protoplasts.

A toxin preparation from Helminthosporium maydis Race T containing several closely related molecules with apparently identical biological activities was highly active against mitochondria and protoplasts from Texas male-sterile (T) cytoplasm corn (T mitochondria and T protoplasts, respectively) but had no effect on their male-fertile (N) cytoplasm counterparts. The toxin preparation caused multiple changes in isolated T mitochondria, including uncoupling of oxidative phosphorylation, stimulation of succinate and NADH respiration, inhibition of malate respiration, increased swelling, loss of matrix density, and unfolding of the inner membrane. Only 6 to 7 nanograms toxin per milligram mitochondrial protein (1.8 nanogram per milliliter) were required to fully uncouple oxidative phosphorylation and to completely inhibit malate respiration in isolated T mitochondria. Similar low concentrations of toxin caused collapse of T protoplasts after several days of culture. Severe ultrastructural damage to mitochondria in T protoplasts was observed within 20 minutes; no changes in other cellular components were observed at this time. These observations on the cytoplasmic specificity, multiple effects, and high activity of the toxin at the mitochondrial and cellular levels highlight its biological significance and potential usefulness in determining the molecular basis of southern corn leaf blight disease.

Journal Article↗