Search PubMed⌕ Search

Biomedical subjects

M Alexander

Publications and source records attributed to M Alexander.

At least 343 records · Page 19Linked to original sources
PubMed1976

The effect of diet on hepatic bile formation and bile acid metabolism in squirrel monkeys with and without cholesterol gallstones.

In order to explain why squirrel monkeys on some experimental diets develop cholesterol gallstones, we made a number of measurements on bile acid kinetics and on bile secretion and composition. The pool size of cholic acid was much greater in monkeys on a commercial diet than in any group on a semipurified diet. It was also greater in squirrel monkeys on a lithogenic diet but without gallstones than in monkeys from the same diet group with gallstones. The half-lives of cholic acid tended to be proportional to pool size, and absolute rates of cholic acid synthesis were, therefore, not much affected by diet. Diet did not affect the pool sizes and half-lives of chenodeoxycholic acid as much as those of cholic acid. Dietary cholesterol increased concentrations of cholesterol relative to bile acids and phospholipids in hepatic bile as well as absolute secretory rates of all three components. Interruption of the enterohepatic circulation of bile in fasted monkeys with gallstones resulted in a more rapid and marked increase in the relative cholesterol concentration and decline in the absolute concentration of bile acids in hepatic bile than occurred for monkeys without gallstones. This was due to the low proportion of the bile acid pool outside the gallbladder and the low rate of new bile acid synthesis of the monkeys with gallstones during fasting.

Animals↗
PubMed1975

The effects of hyperlipidemia on lipoprotein metabolism in squirrel monkeys and rabbits.

We studied the metabolism of different classes of lipoprotein in squirrel monkeys and rabbits. Lipoproteins were labeled in vivo in donor animals with (3H)leucine and (3H)cholesterol. The rate of disappearance from plasma of recipient squirrel monkeys of the protein moiety of the very low density lipoproteins was rapid, that of high density lipoproteins slow, and the rate for low density lipoproteins was intermediate. The fractional turnover of the apoprotein of low density lipoproteins was slightly reduced in hyperlipidemic monkeys, but the absolute rates of synthesis and catabolism were increased. Hyperdipidemia in rabbits resulted in a dramatic reduction in the fractional catabolic rate of low density lipoprotein apoprotein. Hyperlipidemia in the donors of biosynthetic low density lipoproteins also influenced the rates of catabolism in rabbits. We showed the cycloheximide that although there was recycling of (3H)leucine into other proteins, the reutilization of leucine from low density lipoproteins for nascent low density lipoproteins was not significant. In most tissues the ratio of cholesterol:protein radioactivity was much greater than that for plasma 24 h after administration of labeled low density lipoproteins, but the ratios for aortic intima plus inner media and for plasma low density lipoproteins were similar. The presence of atherosclerosis resulted in a large increase in the apparent uptake of low density lipoproteins by the aortas of rabbits and monkeys.

Animals↗
PubMed1975

Protozoa as agents responsible for the decline of Xanthomonas campestris in soil.

A streptomycin-resistant mutant of Xanthomonas campestris was used to assess the persistence of the plant pathogen in soil and the changes in populations that might be important for its survival. In soil into which large numbers of the organism were introduced, a marked decline in its abundance occurred, but after about 1 week its population density reached a level of about 105 and did not continue to fall during the test period. No such marked decline was evident in sterile soil inoculated with X. campestris. The bacterium did not lose viability if starved for carbon or inorganic nitrogen. Although abundant in soil, the numbers of propagules capable of producing antibiotics or lytic enzymes active against X. campestris did not increase coincident with the pathogen's decline, and no increase in tartrate-extractable toxins was observed. Neither bdellovibrios nor bacteriophages active against the xanthomonad were found in the soil, but a marked increase in the frequency of protozoa paralleled the phase of rapid diminution in the X. campestris population. In actidione-treated soil, in which protozoan activity was severly limited, the high cell density of the pathogen was maintained. On the basis of these data, it is concluded that predation by protozoa is responsible for the abrupt fall in frequency of the bacterium in natural soil.

Animals↗
PubMed1975

Regulation of predation by prey density: the protozoan-Rhizobium relationship.

Tetramitus rostratus and strains of Hartmanella, Naegleria, and Vahlkampfia consumed large numbers of Rhizobium meliloti cells in a salt solution, but protozoan multiplication and the bacterial decline stopped when the prey density fell to about 10-6 to 10-7 cells/ml. At higher prey densities, the maximum numbers of Hartmanella sp. and Naegleria sp. were proportional to the quantity of R. meliloti initially provided to the amoebas. When supplemental rhizobia were supplied to Hartmanella sp. or Naegleria sp. after their active feeding had terminated, presumably because the remaining 10-6 or 10-7 bacteria/ml could not be captured, replication of the protozoa was initiated. The rate of elimination of rhizobia present in large populations was proportional to the initial abundance of Naegleria sp., but the final numbers of amoebas and surviving R. meliloti cells were independent of initial numbers of predators. The surviving bacteria were not intrinsically resistant to attack because 98% of the survivors, when concentrated, were consumed. It is suggested that large populations of bacteria in nature may be reduced in size by predatory protozoa, but many of the prey cells will not be eliminated.

Animals↗
PubMed1975

Microbial degradation of polyethylene glycols.

Mono-, di-, tri-, and tetraethylene glycols and polyethylene glycols (PEG) with molecular weight up to 20,000 were degraded by soil microorganisms. A strain of Pseudomonas aeruginosa able to use a PEG of average molecular weight 20,000 was isolated from soil. Washed cells oxidized mono- and tetraethylene glycols, but O2 consumption was not detectable when such cells were incubated for short periods with PEG 20,000. However, the bacteria excreted an enzyme which converted low- and high-molecular-weight PEG to a product utilized by washed P. aeruginosa cells. Gas chromatography of the supernatant of a culture grown on PEG 20,000 revealed the presence of a compound co-chromatographing with diethylene glycol. A metabolite formed from PEG 20,000 by the extracellular enzyme preparation was identified as ethylene glycol by combined gas chromatography-mass spectrometry.

Biodegradation, Environmental↗
PubMed1975

Basis for the resistance of several algae to microbial decomposition.

The basis for the resistance of certain algae to microbial decomposition in natural waters was investigated using Pediastrum duplex, Staurastrum sp., and Fischerella muscicola as test organisms. Enzyme preparations previously found to convert susceptible algae into spheroplasts had no such effect on the resistant species, although glucose and galacturonic acid was released from P. duplex walls. Little protein or lipid but considerable carbohydrate was found in the walls of the refractory organisms, but resistance was not correlated with the presence of a unique sugar monomer. A substance present in Staurastrum sp. walls was characterized as lignin or lignin-like on the basis of its extraction characteristics, infrared spectrum, pyrolysis pattern, and content of an aromatic building block. Sporopollenin was found in P. duplex, and cellulose in Staurastrum sp. Cell walls of the algae were fractionated, and the fractions least susceptible to microbial degradation were the sporopollenin of P. duplex, the polyaromatic component of Staurastrum sp., and two F. muscicola fractions containing several sugar monomers. The sporopollenin content of P. duplex, the content of lignin or a related constituent of Staurastrum sp., and the resistance of the algae to microbial attack increased with age. It is suggested that resistance results from the presence of sporopollenin in P. duplex, a lignin-like material in Staurastrum sp., and possibly heteropolysaccharides in F. muscicola.

Bacteria↗
PubMed1975

Basis for the susceptibility of several algae to microbial decomposition.

Partially purified cellulase and a cellulase-containing polygalacturonase but notlysozyme extensively degraded the walls of Chlamydomonas reinhardtii and Ulothrix fimbrata and converted intact cells of the algae to spheroplasts. A streptomycete cellulase cochromatographed with the enzyme system releasing glucose from walls of these organisms, and this preparation also converted the algal cells to spheroplasts. The dominant constituent in the walls was carbohydrate, and glucose and small quantities of galacturonic acid but no amino sugars were present in acid hydrolysates of the walls. Glucose accounted for essentially all of the material solobilized by the cellulase preparation. Lysozyme acted on Cylindrospermum sp. walls, and it, but not the otherenzymes, converted some of the Cylindrospermum sp. cells to spheroplasts. Streptomycete enzymes lysing Micrococcus lysodeikticus cochromatographed with the proteins releasing reducing sugars from Cylindrospermum sp. walls, and components in the active fraction converted cells of this alga into spheroplasts. X-ray diffraction revealed that the walls of C. reinhardtii and U. fimbrata but not those of Cylindrospermum sp. contained cellulose. The data suggest that the susceptibility of the first twospecies to microbial degradation in natural ecosystems results from an attack on the cellulose in their walls, and the susceptibility of the third is linked with the microbial production of a lysozyme.

Carbohydrates↗
PubMed1975

Protozoa and the decline of Rhizobium populations added to soil.

A fall in Rhizobium abundance occurred in nonsterile soil inoculated with large numbers of the root-nodule bacteria, but many of the rhizobia still survived. No such decline was evident in sterile soil. Protozoa feeding on these bacteria were isolated from soil and other environments. As the abundance of Rhizobium meliloti and a cowpea Rhizobium strain in soil decreased, the protozoan density increased. The inability of the predators to eliminate their prey from soil was not the result of the presence of organisms feeding on the protozoa because many rhizobia survived in sterile soil inoculated with the prey and cultures of individual protozoa, nor was it the result of the rapid multiplication of the bacteria to replace those consumed because survivors were still numerous in essentially organic matter free soil in which the bacteria did not grow appreciably. The lack of elimination also was not associated with a protective effect of soil particles because survivors were still abundant in solutions inoculated with protozoa and bacteria. It is suggested that the size of the prey population diminishes until a density is attained at which the energy used by the predator in hunting for the survivors equals that obtained from the feeding.

Amoeba↗
PubMed1975

Arm-reach capability of USAF pilots as affected by personal protective equipment.

Thirty-two USAF pilots participated in a study to determine the effects of personal protective equipment upon arm-reach capability. The reach envelope of each pilot was measured under two experimental conditions: 1) shirt-sleeved with the inertial reel unlocked; and 2) wearing complete winter flying assembly with the inertial reel locked. Selected descriptive statistics are presented for each of five angular positions. Arm-reach envelopes for various percentile values obtained for the two experimental conditions at 10 knob distances from the deck are shown. The results indicate that there are singificant practical differences in arm-reach capability between the shirt-sleeved and the complete winter flying assembly conditions.

Adult↗
PubMed1975

Anthropometric sizing program for oral-nasal oxygen masks based on 1967 U.S. Air Force survey data.

A new sizing program for oral-nasal masks, based on total facial length, has been developed through an analysis of the 1967 USAF anthropometric survey head and face data. A four-size series of three-dimensional face forms has been sculpted based on this sizing program as a design aid for sizing such masks. This report includes a discussion of the theoretical and practical aspects of the sizing analyses and procedures, and establishes design limits and procurement tariffs for the four sizes of masks. The MBU-12/P oxygen mask, an aoral-nasal pressure-demand type of mask, has been fabricated in accordance with this sizing system using the face forms as sizing guides. The results obtained during fit-tests using 66 USAF personnel as subjects are described. The authors concluded that the dimensional sizing of the oral-nasal oxygen mask facepieces is valid for USAF flight crews.

Aerospace Medicine↗
PubMed1975

Stability of nitrosamines in samples of lake water, soil, and sewage.

N-nitrosodimethylamine, N-nitrosodiethylamine, and N-nitrosodi-n-propylamine were resistant to degradation in soil, sewage, and lake water. No degradation of these nitrosamines was observed in lake water during a 3.5-month period. A lag of nearly 30 days occurred before their slow disappearance from soil; they disappeared slowly from sewage, but a minimum of 50% remained after 14 days. The results with sewage and soil suggesta a microbial involvement in the slow decomposition of these nitrosamines.

Biodegradation, Environmental↗