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T S Johnson

Publications and source records attributed to T S Johnson.

At least 55 records · Page 3Linked to original sources
PubMed1984

Prevention of acute mountain sickness by dexamethasone.

Acute mountain sickness is a syndrome that occurs when unacclimatized persons ascend rapidly to high altitudes. It is postulated that cerebral edema causes its symptoms. Since dexamethasone is useful in treating some forms of cerebral edema, we investigated its role in the prevention of acute mountain sickness. Using a double-blind crossover design, we exposed eight young men to a simulated altitude of 4570 m (15,000 ft) on two occasions. By random assignment, each subject received dexamethasone (4 mg every 6 hours) or placebo for 48 hours before and throughout the 42-hour exposure. The presence of symptoms of acute mountain sickness was established by two methods: a questionnaire and an interview by a physician. Dexamethasone significantly reduced the symptoms of acute mountain sickness. During dexamethasone treatment, the cerebral-symptom score (mean +/- S.E.) decreased from 1.09 +/- 0.18 to 0.26 +/- 0.08, and the respiratory-symptom score decreased from 0.64 +/- 0.09 to 0.31 +/- 0.06 (both, P less than 0.05). As judged by the interviewing physician, the symptom score decreased from 1.10 +/- 0.11 to 0.28 +/- 0.07 (P = 0.01). We conclude that dexamethasone may be effective in preventing the symptoms of acute mountain sickness.

Acute Disease↗
PubMed1984

Cell synchrony techniques. I. A comparison of methods.

Selected cell synchrony techniques, as applied to asynchronous populations of Chinese hamster ovary (CHO) cells, have been compared. Aliquots from the same culture of exponentially growing cells were synchronized using mitotic selection, mitotic selection and hydroxyurea block, centrifugal elutriation, or an EPICS V cell sorter. Sorting of cells was achieved after staining cells with Hoechst 33258. After synchronization by the various methods the relative distribution of cells in G1, S, or G2 + M phases of the cell cycle was determined by flow cytometry. Fractions of synchronized cells obtained from each method were replated and allowed to progress through a second cell cycle. Mitotic selection gave rise to relatively pure and unperturbed early G1 phase cells. While cell synchrony rapidly dispersed with time, cells progressed through the cell cycle in 12 hr. Sorting with the EPICS V on the modal G1 peak yielded a relatively pure but heterogeneous G1 population (i.e. early to late G1). Again, synchrony dispersed with time, but cell-cycle progression required 14 hr. With centrifugal elutriation, several different cell populations synchronized throughout the cell cycle could be rapidly obtained with a purity comparable to mitotic selection and cell sorting. It was concluded that, either alone or in combination with blocking agents such as hydroxyurea, elutriation and mitotic selection were both excellent methods for synchronizing CHO cells. Cell sorting exhibited limitations in sample size and time required for synchronizing CHO cells. Its major advantage would be its ability to isolate cell populations unique with respect to selected cellular parameters.

Animals↗
PubMed1984

Cell synchrony techniques. II. Analysis of cell progression data.

CHO cells which have been sorted by mitotic detachment, centrifugal elutriation and fluorescence activated cell sorting have been followed for up to 14 hr by flow cytometry to examine their progression characteristics. Mathematical modelling techniques were used to provide quantitative estimates of the cell-cycle parameters. Mitotic detachment gives an 11.2-hr cycle time with mean transit times TG1, TS and TG2M equal to 3.2, 5.6 and 2.4 respectively. Cells prepared by central elutriation in an early G1 state have a 14-hr cycle time with TG1, TS and TG2M of 5.7, 6.0 and 2.3 hr. Populations prepared by centrifugal elutriation enriched in early S and late S and G2M have transit times of 2.7, 5.9 and 1.6 hr and 4.9, 6.7 and 2.1 hr with cycle times of 11.2 and 13.2 hr respectively. Cell sorting for a G1 population gives transit times of 9.8, 8.0 and 3.6 for an overall 21.4-hr cycle time.

Animals↗
PubMed1983

Sympathoadrenal responses to acute and chronic hypoxia in the rat.

The sympathoadrenal responses to acute and chronic hypoxic exposure at 10.5 and 7.5% oxygen were determined in the rat. Cardiac norepinephrine (NE) turnover was used to assess sympathetic nervous system (SNS) activity, and urinary excretion of epinephrine (E) was measured as an index of adrenal medullary activity. The responses of the adrenal medulla and SNS were distinct and dependent upon the degree and duration of hypoxic exposure. Chronic hypoxia at 10.5% oxygen increased cardiac NE turnover by 130% after 3, 7, and 14 d of hypoxic exposure. Urinary excretion of NE was similarly increased over this time interval, while urinary E excretion was marginally elevated. In contrast, acute exposure to moderate hypoxia at 10.5% oxygen was not associated with an increase in SNS activity; in fact, decreased SNS activity was suggested by diminished cardiac NE turnover and urinary NE excretion over the first 12 h of hypoxic exposure, and by a rebound increase in NE turnover after reexposure to normal oxygen tension. Adrenal medullary activity, on the other hand, increased substantially during acute exposure to moderate hypoxia (2-fold increase in urinary E excretion) and severe hypoxia (greater than 10-fold). In distinction to the lack of effect of acute hypoxic exposure (10.5% oxygen), the SNS was markedly stimulated during the first day of hypoxia exposure at 7.5% oxygen, an increase that was sustained throughout at least 7 d at 7.5% oxygen. These results demonstrate that chronic exposure to moderate and severe hypoxia increases the activity of the SNS and adrenal medulla, the effect being greater in severe hypoxic exposure. The response to acute hypoxic exposure is more complicated; during the first 12 h of exposure at 10.5% oxygen, the SNS is not stimulated and appears to be restrained, while adrenal medullary activity is enhanced. Acute exposure to a more severe degree of hypoxia (7.5% oxygen), however, is associated with stimulation of both the SNS and adrenal medulla.

Adrenal Medulla↗
PubMed1983

Cytophotometric measurement of the cellular DNA content of [3H]thymidine-labelled spheroids. Demonstration that some non-labelled cells have S and G2 DNA content.

Spheroids from the V279-171b and MCa-11 cell lines were incubated continuously for 24 hr in [3H]thymidine for labelling of the outer cells of the viable rim. The spheroids were dispersed into single cells, and the DNA content of photomapped cells was measured by absorption cytophotometry. Autoradiographs were then prepared from which we ascertained cellular labelling. For spheroids of both cell lines, we found a larger proportion of cells with a G0/G1 DNA content among the non-labelled inner spheroid cells than among the labelled outer cells (P less than 0.001). This block of non-labelled spheroid cells in G0/G1 was not a cell cycle perturbation caused by the isotope for the MCa-11 spheroids. Approximately 8% of non labelled MCa-11 spheroid cells had S/G2 DNA content, suggesting that non-cycling cells in spheroids may be blocked in S and G2 as well as in the G0/G1 phase of the cell cycle.

Animals↗
PubMed1982

Restricted food intake limits brown adipose tissue hypertrophy in cold exposure.

Two factors that may determine brown adipose tissue (BAT) hypertrophy during conditions of increased metabolic heat production are increased food intake and increased sympathetic nervous system (SNS) activity. Since these two proceed pari passu during cold exposure, their independent contributions to BAT hypertrophy are unknown. To examine the role of each, we limited the food intake of a group of cold exposed rats by pair feeding them to warm exposed control rats and then compared the pair fed rats to ad lib fed cold exposed animals. Restricted food intake limited absolute BAT hypertrophy (0.226 +/- 0.01 g. vs 0.488 +/- 0.02 g, pair fed vs ad lib, P less than 0.01), BAT as per cent body weight (0.189 +/- 0.12 vs 0.252 +/- 0.012, P less than 0.01) and BAT protein content (34.4 +/- 3.8 vs 48.9 +/- 2.6 mg, P less than 0.01) despite evidence of quantitatively similar activation of the SNS in BAT in both groups. We conclude that increased food intake contributes to BAT hypertrophy in cold exposure independent of sympathetic activity.

Adipose Tissue, Brown↗
PubMed1982

Naloxone does not affect bronchoconstriction induced by isocapnic hyperpnea of subfreezing air.

Although respiratory heat loss with cooling of the tracheobronchial mucosa is responsible for the airway obstruction that develops after inhalation of subfreezing air in asthmatics, the mechanism by which airway cooling results in bronchoconstriction is not known. In order to test whether release of endogenous opiate peptides might play a role in mediating this response, asthmatic subjects were studied before and after isocapnic hyperventilation of subfreezing air after the administration of placebo or naloxone, given in a double-blind fashion. Five asthmatic subjects were tested with low-dose (0.8 mg) and 5 with high-dose (10 mg) naloxone given intravenously. Pretreatment with naloxone at either dose did not attenuate the decrease in FVC, FEV1, or FEF25--75 after cold air in comparison with placebo pretreatment. A slightly greater decrease in FEV1 and FEF25--75 after low-dose naloxone than placebo pretreatment can be partially explained by a difference in the temperature achieved during cold air inhalation. We conclude that endogenous opiate peptides are not involved in mediating the bronchoconstrictor response to cold air inhalation in asthmatics.

Adult↗
PubMed1981

Flow cytometric electronic direct current volume and radiofrequency impedance measurements of single cells and particles.

A flow-system instrument is described that uses direct current and radiofrequency (rf) currents to detect simultaneously the low and high frequency impedance changes produced by biologic cells or particles suspended in saline traversing through a 93um diameter sensing orifice. For nonmembranous particles and plastic microspheres both the Coulter direct current volume and rf-parameter signals are proportional to particle volume. Cells having an intact plasma membrane produce rf-impedance changes dependent additionally on the electrical properties of the plasma membrane and intracellular structures. Thus, biologically different cells having the same Coulter direct current volume can be distinguished if they differ in their electrical rf impedance properties.

Animals↗
PubMed1981

Norepinephrine turnover in lung: effect of cold exposure and chronic hypoxia.

The lung contains sympathetic efferent nerves, but their participation in conditions associated with sympathetic nervous system activation is unknown. To assess sympathetic activity in lung during cold exposure and hypoxia, the measurement of radiolabeled norepinephrine (NE) turnover was carried out in this organ. In preliminary studies this technique, which measures in vivo the activity of sympathetic nerves in an individually innervated organ, was validated for use as a measure of sympathetic activity in rat lung. NE turnover was then measured in unanesthetized rats during cold (4 degrees C, 24 h) and hypobaric hypoxic (PB = 380 Torr, 7 days) exposure. Cold exposure increased calculated NE turnover rate in lung by 63% from 4.2 +/- 1.4 to 6.8 +/- 1.6 ng NE.organ-1.h-1 (95% confidence limits). Chronic hypobaric hypoxia increased NE turnover rate in lung by 114% from 4.0 +/- 1.8 to 8.6 +/- 2.4 NE.organ-1.h-1. Thus NE turnover techniques are applicable to rat lung and demonstrate increased sympathetic activity during cold exposure and chronic hypoxia.

Animals↗
PubMed1981

Increased accuracy of absorption cytophotometric DNA values by control of stain intensity.

A method of improving absorption cytophotometric cellular DNA values by making measurements on Feulgenstained cells at optimal stain absorbances has been developed. Stain intensity can be controlled either by alteration of the Feulgen staining reaction or by selection of "off-peak" wavelengths of light for cytometry. The use of chicken red blood cells as an internal standard, and of a computerized cytometer for the measurements, allows selection of the appropriate off-peak light wavelengths, correction for staining variability at different sites on the same slide, and rapid calculation of cellular DNA values. Cytometry can also be performed at controlled absorbance levels on autoradiographs of 3H-thymidine-labeled cells to allow direct study of the DNA content of nonlabeled G1/G0 and G2/M cells. Use of this technique on mixtures of mouse thymocytes, spleen cells, bone marrow cells, and liver cells gave essentially identical values for G1/G0 cellular DNA content, with coefficients of variation of less than 3%.

Animals↗
PubMed1981

Ploidy and DNA distribution analysis of spontaneous dog tumors by flow cytometry.

Ploidy and DNA content distributions were measured for 68 biopsy specimens of spontaneous (solid) dog tumors using flow cytometry analysis of mithramycin-stained cells. The tumor ploidy (i.e., DNA index values) ranged from 1.0 to 4.0 (diploid = 1.0), with a mean of 1.4. More than 80% of the tumors had elevated G0-G1 peak DNA contents and were classified heteroploid, similar to human solid tumors. Six mammary carcinomas and osteosarcomas had bimodal G0-G1 peaks. Based on flow cytometric data and pathology criteria, it was observed that: (a) the percentage of tumor S-phase cells tended to increase with increasing DNA index; and (b) for a given DNA index, the percentage of S-phase cells was lower for well-differentiated tumors and higher for poorly differentiated tumors. The inherent scattering of the DNA content and DNA distribution data between different tumor types limited the usefulness of these data for classifying tumors. The results suggest that improved classification of cytologically different tumors and tumor subsets might be achieved by simultaneous flow measurement of DNA content and DNA distribution information with an additional parameter that detects the cytological differentiation state.

Animals↗