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Biomedical subjects

L H Stevenson

Publications and source records attributed to L H Stevenson.

11 recordsLinked to original sources
PubMed1990

Pharmacokinetics in old age.

All practising clinicians will be aware of the increased number of elderly patients requiring drug treatment as the proportion of people over the age of 65 increases in our Western society. The elderly as a group have much to benefit from modern drug therapy, but, historically, are also the group most prone to adverse drug reactions. Such reactions have often been due to inappropriate drug prescribing based on an incomplete knowledge of changes in drug handling with age. In recent years there has been an increased understanding of the physiological changes of ageing and the changes in drug handling consequent upon these changes. This review will concentrate on the clinical sequelae of changes in drug handling and suggest areas where modification in prescribing practice may yield clinical benefits and lessen the toll of adverse drug reactions.

Aged↗
PubMed1982

Seasonal variability and transport of suspended microfungi in a southeastern salt marsh.

Tidally induced fluctuations and transports of microfungi were investigated. Samples were collected at three depths from three stations positioned at a transect in a large salt marsh creek. Samples were taken every 1.5 h for 50 consecutive h during neap tides and 50 consecutive h during the corresponding spring tides. In each season, microfungi concentrations fluctuated out of phase with the tides during both neap and spring tides. Mean concentrations of suspended microfungi did not vary appreciably throughout the year. Fungi were exported from the marsh during the majority of the tidal cycles studied. The results suggest that microfungi may serve as indicators of water mass movements.

Journal Article↗
PubMed1981

The assay of adenosine 5'-triphosphate extracted from salt-marsh microbiota.

The light-emitting reaction of firefly luciferin and luciferase is a common ingredient in the quantification of adenosine triphosphate (ATP) extracted from the microbiota of environmental samples. Both portions of the light-emission phase of the luciferase reaction, the primary flash within 3 s of mixing and the secondary decay in the luminescence following the flash, have been used to quantify extracted ATP. However, the magnitude of the secondary phase is influenced by nucleotides other than ATP. The impact of this influence on the quantification of ATP was studied in samples collected from the water covering a salt marsh. Analysis by integration of the secondary decay portion of the emission yielded values of ATP per cubic metre that were consistently higher than those obtained by peak height analysis of the same extracts. Assays using the integration technology resulted in values that were up to 8 (mean = 3.6) times higher than corresponding values determined by peak height analysis in unfractionated samples (total microbial biomass) and up to 16 (mean = 4.8) times higher in water that had been prefiltered with a 1.0 micrometer filter (bacterial biomass).

Adenosine Triphosphate↗
PubMed1979

Adenosine 5'-triphosphate flux through the north inlet marsh system.

The distribution, fluctuation, and short-term transport of total microbial biomass (measured as adenosine 5'-triphosphate [ATP]) was investigated in a large salt marsh creek. Hourly samples were collected synoptically for 25 h from 10 boats positioned across the 320-m width of the creek. Samples were collected from three depths ranging from 0.2 to 8.0 m. Hourly data obtained from each station were graphed, plotting depth against ATP. Subsequently, interpolated ATP values were generated for every one-tenth depth from the surface to the bottom with the use of an 11-point proportional divider. A total of 2,750 values were generated, and a mean value of 0.865 mg of ATP per m was determined. Maximum levels of ATP were found at high tide and minimal values were found at low tide. The distribution of ATP concentrations was found to be complex, with no suggestion of vertical stratification; however, horizontal divisions were apparent. ATP values corrected for direction of flow or velocity indicated two ebb-directed channels; however, when considered in total, there was a net import of ATP through the interface. The total import of ATP for this 25-h sampling period was calculated to be 3.58 kg, corresponding to a net transport of 39.8 mg of ATP per s through the cross section. Results suggest that detailed characterization of a creek transect in terms of ATP or any similar parameter requires the simultaneous measurements of both the concentration of the parameter in question and the velocity at the time and point from which the sample was taken.

Journal Article↗
PubMed1978

Microbiological and physical properties of salt marsh and microecosystem sediments.

Sediments from natural marsh and four microecosystem (MES) tanks were compared with reference to ATP, carbon content, and physical properties. Mean values for bacterial numbers and ATP were about twice as high in the MES, carbon content was slightly higher in the artificial systems, and the sediment of the MES was enriched for larger grain sizes and depleted of silt and clay. In the natural marsh sediment, ATP was strongly related (Pearson's correlation coefficient) to granulometric (or physical) factors, whereas ATP was related to biological factors in the MES. Approximately 61% of the variation in ATP concentrations in the marsh sediments could be accounted for by the parameters measured. Only half that amount could be explained on the basis of those same variables in the MES. Furthermore, one of the four tanks was significantly different from the other three in terms of ATP concentration, and an anomaly in respect to silt-clay content was demonstrated in another. Careful control and some type of equilibrating procedure will be necessary before the MES can be employed as replicate units.

Journal Article↗
PubMed1978

The transport of microbial biomass and suspended material in a high-marsh creek.

The transport of microbial biomass and suspended material in a high-marsh creek was investigated during four 40-h tidal studies throughout the year. Although considerable differences were noted between successive tidal cycles, overall the creek was found to be an exporting system and transported a mean concentration of ATP (-33g), chlorophyll a (-66g), particulate organic carbon (-31kg), total suspended material (-344kg), and fixed suspended material (-195kg) during each tidal cycle. This net outward flux of materials was associated with a net flow of water out of creek, while the net import of aerobic, heterotrophic bacteria (43 x 10(12)) and volatile suspended material (238kg) was generally due to higher mean concentrations of these materials per unit volume of water during the flooding tide. Also the latter generally were associated with increased amounts of suspended material suggesting an association between bacteria and suspended matter.

Adenosine Triphosphate↗
PubMed1976

Computer-assisted analysis of adenosine triphosphate data.

A computer program has been written to assist in the analysis of adenosine 5'-triphosphate data. The program is designed to calculate a dilution curve and to correct sample and adenosine 5'-triphosphate standard data for background and dilution effects. In addition, basic statistical parameters and estimates of biomass carbon are also calculated for each group of samples and printed in a convenient format. The versatility of the program to analyze data from both qauatic and terrestrial samples is noted as well as its potential use with various types of instrumentation and extraction techniques.

Adenosine Triphosphate↗
PubMed1966

Cyst formation and poly-beta-hydroxybutyric acid accumulation in Azotobacter.

Stevenson, L. H. (Louisiana State University, Baton Rouge), and M. D. Socolofsky. Cyst formation and poly-beta-hydroxybutyric acid accumulation in Azotobacter. J. Bacteriol. 91:304-310. 1966.-The relationship between cyst formation and the accumulation of poly-beta-hydroxybutyric acid (PHB) in Azotobacter vinelandii (A. agilis) was investigated. After various periods of growth, the cells were harvested, and the amount of PHB and the extent of encystment were determined. The polymer content of the cells increased sharply and reached a maximum on the 2nd day of growth followed by a gradual decline as the culture aged. At maximal accumulation, the PHB content was 35% of the dry weight, and the PHB-nitrogen ratio was 11:1. Those substrates promoting the highest polymer content (glucose, butanol) also promoted 95 to 100% encystment. Manipulation of the carbon and nitrogen supply in the medium indicated that both the maximal PHB content and the extent of cyst formation could be controlled. A direct correlation was noted between the amount of polymer accumulated and the percentage of cysts formed, indicating a possible role of PHB as a carbon or energy source, or both, for the encystment process.

Azotobacter↗