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R A Walters

Publications and source records attributed to R A Walters.

70 records · Page 4Linked to original sources
PubMed1970

Radiosensitivity of mammalian cells. IV. Effects of x-irradiation on the DNA synthetic period in synchronized cells.

The effect of X-irradiation on the timing of DNA synthesis in the Chinese hamster ovary cells has been investigated. Mitotically synchronized cells irradiated in mitosis or early G(1) exhibited a fixed, dose-independent (150-2000 rad) delay of 1.6 hr in entry into S, while the duration of S was unaffected. Cells irradiated during late G(1) or the first 0.8 hr of S were not affected either in time of initiation or duration of S. However, when cells 0.8 hr or more into S were irradiated, completion but not initiation of DNA synthesis was delayed, indicating a very precise separation of X-ray effects upon initiation and replication. There was no indication of a re-ordering of cells following irradiation and recovery, since cells in G(2) at the time of irradiation always divided before cells irradiated in S. The results suggest that two separate functions required for initiation and continued replication of DNA may be differentially sensitive to X-irradiation.

Animals↗
PubMed1969

Radiosensitivity of mammalian cells. 3. Effect of suboptimal growth temperatures on recovery from radiation-induced division delay.

We investigated the effect of suboptimal growth temperatures on recovery from radiation-induced division delay in Chinese hamster cells. It was found that no recovery occurred during the time that either log-phase or synchronized populations were incubated at 4 degrees C and that injury sustained at low dose rates was cumulative over a period of 6.2 hr at low temperature. Postirradiation conditions influencing recovery from the induced division delay period are different from those affecting survival, suggesting that biochemical damage leading to division delay may be different from that leading to cell death.

Animals↗
PubMed1969

Retinoblastoma.

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Child↗
PubMed1968

Radiosensivity of mammalian cells. I. Timing and dose-dependence of radiation-induced division delay.

The time of onset and duration of division delay induced by exposure to 250-kvp x-irradiation have been measured in several mammalian cell lines grown in suspension culture. Unique times of action (i.e. interval from irradiation to cessation of division) late in G(2) are characteristic for HeLa, L-5178Y, and Chinese hamster cells, and the time of action is independent of dose over the range 25-800 rads. The duration of delay was directly proportional to dose; all irradiated cells divided at least once and maintained their relative positions in the life cycle for periods exceeding one generation time. Neither random nor synchronous cultures exposed at varying times in the life cycle exhibited differences in radiation sensitivity measured either by onset or duration of the delay period. The time of action was experimentally indistinguishable from the point marking completion of protein synthesis essential for division, leading to speculation that division delay involves a translation defect.

Animals↗
PubMed1968

Radiosensitivity of mammalian cells. II. Radiation effects on macromolecular synthesis.

Radiation effects on macromolecular synthesis essential for the Chinese hamster cell to traverse the life cycle and to divide have been investigated. Life-cycle analysis techniques employing inhibitors of macromolecular synthesis were used in determining the kinetics of cell growth for specific segments of the population following spontaneous recovery from radiation-induced division delay. The results indicated that recovery does not occur in the absence of functional protein synthesis. Under conditions which inhibit normal RNA and DNA synthesis, irradiated cells can recover the capacity to traverse the life cycle and to divide. The stability of mRNA species coding for proteins essential for division in irradiated cells was also measured. The mean functional lifetime of these mRNA species was 1 hr. The data demonstrate the existence of a specific segment of the population consisting of cells which have completed transcription related to division but not concomitant translation and which can recover from the radiation injury without synthesis of additional RNA. Thus, initial recovery of the ability to divide has an obligate requirement for protein synthesis but no corresponding requirement for nucleic acid synthesis during the period when original messenger remains intact.

Animals↗
PubMedDate not supplied

Left ventricular support with the implantable AB-180 centrifugal pump in sheep with acute myocardial infarction.

A small, 257 g centrifugal pump was tested as a left ventricular assist device (LVAD) in sheep given a myocardial infarction. Pump performance, hemolysis, end organ function, weaning, explant procedure, and the incidence of thromboemboli at autopsy were studied over intervals of 1 to 44 days. Twelve sheep were given acute myocardial infarction by ligation of the anterior descending coronary artery and 11 had insertion of the AB-180 Circulatory Support System (CSS). One sheep served as a control for the space occupying effects of the pump in the left chest. Inflow was from the left atrium and outflow was to the descending thoracic aorta. Heparin (57-83 U/ml) in sterile water was infused into the pump at a rate of 10 ml/hr. Pump flows of 1-5.7 L/min were tested. The AB-180 CSS supported 73.5% of the total cardiac output (pump + heart) of 3.89 L/min, with a mean arterial pressure of 86 +/- 7 mmHg at a pump speed of 4,162 +/- 276 rpm immediately after implant. Hemolysis was <10 mg/dl and activated partial thromboplastin time (aPTT) values were in the normal range for sheep (<52 sec) after 48 hr of pumping. Liver enzyme concentrations returned to normal within 2 weeks. There was no evidence of thrombocytopenia. No signs of infection were present during assist and none was found at autopsy. The device was successfully removed three times without the use of pressor agents or blood transfusion. Alarm systems performed appropriately. During the 106 days of cumulative pumping, two sheep showed small (<1.5 cm) renal infarcts. Both were associated with intervals of pump stasis. The AB-180 CSS pump was easily implanted into the left chest without the use of cardiopulmonary bypass. It appears to have a low thromboembolic potential in sheep, without the need for large doses of heparin to elevate aPTT values. This characteristic may ameliorate the excessive bleeding seen clinically with current LVAD systems used for post cardiotomy cardiogenic shock, which require anticoagulation with heparin. The small size and weight of the device permit implantation within the chest and allow chest closure. This may reduce the incidence of infection associated with temporary left ventricular assist and an open sternum.

Animals↗
PubMedDate not supplied

Clinical and microbial evaluation of treatment regimens to reduce denture stomatitis.

This study evaluated the effect of an antimicrobial mouthrinse, denture soft relines, and a placebo rinse on the clinical findings and microbial flora of 78 patients with denture stomatitis. For 28 days the study and control groups performed oral rinses and denture soaks. Reline group patients had maxillary denture soft relines that were changed every 7 days. At the end of the study, the mean severity of denture stomatitis was significantly less in the groups that used the study rinse (P less than 0.01) and received denture relines (P less than 0.05) compared to the control. Analysis of variance revealed significant differences in ranked adjusted percentage counts in two out of 13 denture plaque organisms investigated (Fusobacterium nucleatum [P less than 0.05] and total Bacteroides [P less than 0.05]), with the antiseptic rinse producing the lowest count. Yeast populations were reduced, but not significantly (P = 0.07). In the absence of other mechanical denture hygiene procedures, the antiseptic rinse and relines were equally effective in reducing denture stomatitis and potential pathogens of denture plaque flora.

Adult↗