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Biomedical subjects

M Alexander

Publications and source records attributed to M Alexander.

At least 253 records · Page 14Linked to original sources
PubMed1981

Effects of long-term protein deficiency on plasma lipoprotein concentrations and metabolism in rhesus monkeys.

Lipoprotein concentrations and metabolism were studied in 5- and 9-year-old rhesus monkeys (Macaca mulatta). Both age groups had been divided into control (13.8% of the calories as protein) and low-protein (3.7% protein) subgroups at birth. All were tested before and after their dietary lipid was changed from corn oil to butter plus cholesterol. The concentrations of very-low-density and high density2 lipoproteins (VLDL and HDL2) tended to be higher in monkeys of the low-protein group, and butter plus cholesterol accentuated the difference. All monkeys of the low protein group had elevated levels of at least one of these two classes of lipoproteins. The secretion of nascent VLDL (after intravenous Triton WR-1339) was greater in the low protein than in the control group when both were fed butter plus cholesterol, and rates of VLDL secretion showed a strong positive correlation with the fasting levels of VLDL. Thirty minutes after the intravenous administration of heparin, VLDL triglyceride was almost completely removed, and the apolipoprotein was reduced by 40%; VLDL cholesteryl esters were unchanged. There was a simultaneous decrease in the intermediate density lipoproteins (IDL) and an increase in HDL2, but the low density lipoproteins (LDL) and HDL2 did not change. The rate of VLDL protein removal from plasma was greater in the low protein than in the control group, and the rates for individual monkeys correlated with the levels of VLDL and HDL2 prior to heparin administration. Hepatic postheparin lipase measured in vitro with saturating levels of substrate was significantly higher in the plasma of control than in that of low protein monkeys.

Animals↗
PubMed1981

Effect of protozoa on bacterial degradation of an aromatic compound.

Prototrophic and growth factor-requiring strains of Alcaligenes spp. were used to study the effect of a protozoan, Tetrahymena pyriformis, on the degradation of p-aminobenzoate. The protozoan inhibited activity of the prototrophic bacterium by reducing its population size. For the growth factor-requiring strain of Alcaligenes, T. pyriformis provided the required growth factors so that the predator permitted the bacteria to grow and to continue p-aminobenzoate degradation. T. pyriformis inhibited bacterial activity when the amino acid supply was in excess, but activity of the auxotrophic strain of Alcaligenes was stimulated by the protozoan when the amino acid supply was limiting, although the bacterial population size was reduced by the protozoan.

Journal Article↗
PubMed1981

Fungicide Enhancement of Nitrogen Fixation and Colonization of Phaseolus vulgaris by Rhizobium phaseoli.

The number and weight of pods and the weight and nitrogen content of the tops of beans (Phaseolus vulgaris) derived from seeds inoculated with a thiram-resistant strain of Rhizobium phaseoli were increased if the seeds were treated with thiram before sowing in soil. A greater percentage of the nodules on 21-day-old plants were derived from the resistant strain, more nodules were formed, and these nodules were more effective in the presence of the fungicide than in its absence. These differences in nodule numbers were no longer present in 56-day-old plants, and only a small percentage of the nodules contained the resistant strain. The abundance of the fungicide-tolerant R. phaseoli increased rapidly soon after planting the seed and subsequently fell markedly, but the rate of decline was less if the seeds had been treated with the chemical. Protozoa also proliferated if thiram had not been applied to the seed, but their numbers were deleteriously influenced by thiram. Bdellovibrio, bacteriophages, and lytic micro-organisms acting on R. phaseoli were rare under these conditions. Ciliates and flagellated protozoa were initially suppressed by planting thiram-coated bean seeds in nonsterile soil, but the former were inhibited longer than the latter and the ciliate numbers never fully recovered if the seeds were treated with the fungicide. The resistant strain grew well in sterile soil also inoculated with a protozoa-free mixture of soil microorganisms whether thiram was added or not, but after an initial rise in numbers, its abundance fell if the mixture contained protozoa; the rate of this fall was delayed by the fungicide. The numbers of R. phaseoli were consistently less in sterile soil inoculated with the rhizobium plus a mixture of soil microorganisms containing ciliates and other protozoa than if the inoculum contained other protozoa but no ciliates. These results suggest that a suppression of protozoa, and possibly especially the ciliates, accounts for the enhanced growth of beans and the greater initial frequency of nodules formed by the thiram-resistant R. phaseoli in the presence of this fungicide. Thiram applied to uninoculated seed enhanced bean growth if thiram-resistant R. phaseoli were present in soil.

Journal Article↗
PubMed1981

Microbial formation of secondary and tertiary amines in municipal sewage.

Dimethylamine was formed in municipal sewage that was amended with creatinine, and trimethylamine was formed from choline or phosphatidylcholine. The maximum level of product that accumulated was equivalent to 0.13, 0.096, and 6.7% by weight, respectively, of the added chemicals. No dimethylamine or trimethylamine was detected in sewage amended with betaine, and no dimethylamine was found in sewage that was amended with methylamine and methionine.

Anaerobiosis↗
PubMed1981

Enhancement of the microbial dehalogenation of a model chlorinated compound.

A number of chlorinated aromatic and aliphatic compounds were dehalogenated when incubated with sewage. Preincubating the sewage with nonchlorinated organic substrates enhanced the subsequent dehalogenation of the chlorinated chemicals. Dehalogenation of 4-chloro-3,5-dinitrobenzoic acid (CDBA) in lake water occurred as a result of microbial growth both in the light in the absence of added nutrients and in the dark in the presence of acetate. No organism able to use CDBA as a carbon source was isolated. Axenic bacterial cultures and a nonaxenic Chlamydomonas culture released chloride from CDBA. The metabolism of CDBA by the latter culture, a process that was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, yielded a product that was identified as alpha-hydroxymuconic semialdehyde. This product of an apparent cometabolic transformation was mineralized by a strain of Streptomyces, thus suggesting that certain cometabolic products may not accumulate because they are carbon sources for other species.

Journal Article↗
PubMed1981

Survival of Rhizobium in Acid soils.

A Rhizobium strain nodulating cowpeas did not decline in abundance after it was added to sterile soils at pH 6.9 and 4.4, and the numbers fell slowly in nonsterile soils at pH 5.5 and 4.1. A strain of R. phaseoli grew when added to sterile soils at pH 6.7 and 6.9; it maintained large, stable populations in soils of pH 4.4, 5.5, and 6.0, but the numbers fell markedly and then reached a stable population size in sterile soils at pH 4.3 and 4.4. The abundance of R. phaseoli added to nonsterile soils with pH values of 4.3 to 6.7 decreased similarly with time regardless of soil acidity, and the final numbers were less than in the comparable sterile soils. The minimum pH values for the growth of strains of R. meliloti in liquid media ranged from 5.3 to 5.9. Two R. meliloti strains, which differed in acid tolerance for growth in culture, did not differ in numbers or decline when added to sterile soils at pH 4.8, 5.2, and 6.3. The population size of these two strains was reduced after they were introduced into nonsterile soils at pH 4.8, 5.4, and 6.4, and the number of survivors was related to the soil pH. The R. meliloti strain that was more acid sensitive in culture declined more readily in sterile soil at pH 4.6 than did the less sensitive strain, and only the former strain was eliminated from nonsterile soil at pH 4.8; however, the less sensitive strain also survived better in limed soil. The cell density of the two R. meliloti strains was increased in pH 6.4 soil in the presence of growing alfalfa. The decline and elimination of the tolerant, but not the sensitive, strain was delayed in soil at pH 4.6 by roots of growing alfalfa.

Journal Article↗
PubMed1981

Tobramycin levels in cerebrospinal fluid of patients with slightly and severely impaired blood-cerebrospinal barrier.

Concentrations of tobramycin in cerebrospinal fluid (CSF) and serum of neurosurgical and of meningitis patients were determined following systemic application of 80-mg doses. Tobramycin was detectable only in 8 tests out of 17 in CSF of 11 neurosurgical patients. The highest drug amount in CSF in these tests was 0.47 microgram/ml. In CSF of 7 meningitis patients with CSF cell counts ranging from 173/3 to 20,500/3 cells, tobramycin was detectable in all 11 determinations. However, the tobramycin level was above 1.0 microgram/ml in only one CSF sample. These results also confirm the poor penetrability of aminoglycosides through the blood-CSF barrier for tobramycin. In proven gram-negative bacillary meningitis and tobramycin treatment, additional intraventricular aminoglycoside application is necessary to obtain effective levels in CSF. An exception may be treatment of neonatal meningitis.

Anti-Bacterial Agents↗
PubMed1980

Metabolism of free and esterified cholesterol and apolipoproteins of plasma low and high density lipoproteins.

We studied the patterns of equilibration of free and esterified cholesterol between lipoprotein fractions of plasma separated by heparin-Mn2+ and of their disappearance from plasma and appearance in liver and bile. Free or esterified [4-14C]cholesterol in low density lipoproteins (LDL) and [7(n)-3H]cholesterol in high density lipoproteins (HDL2 or HDL3) were incubated together with plasma or injected simultaneously into squirrel monkeys. The isotope was alternated for successive experiments. Free cholesterol was equilibrated completely between lipoprotein classes within 30-45 min, but esterified cholesterol was not completely equilibrated within 2 h. Within 10 min after the injection of lipoproteins that had labeled free cholesterol, the bile contained labeled free cholesterol and within 20 min labeled bile acids. Both biliary cholesterol and bile acids initially were enriched 5-10-fold with the isotope that was originally contained in plasma HDL. Hepatic cholesterol was less enriched than bile cholesterol with the isotope of HDL. There was much less incorporation of radioactivity into biliary cholesterol and bile acids after the injection of [7(n)-3H]cholesteryl esters in HDL2 or HDL3 and [4-14C]cholesterol esters in LDL than after labeled free cholesterol, and there was little preference for cholesterol from one lipoprotein class. Although cholesteryl esters were equilibrated slowly between lipoprotein classes, their overall rate of removal from plasma was identical to that for the apolipoproteins of 125I-labeled LDL and 125I-labeled HDL during the first 2 h after injection. Labeled free cholesterol initially disappeared from the plasma compartment several times more rapidly than the esterified form or the lipoprotein apolipoprotein. Thus, cholesteryl esters probably interact with cells as part of intact lipoproteins, since they are not exchanged with cellular cholesterol like plasma free cholesterol.

Animals↗
PubMed1980

[Types of hepatitis in parenteral opiate addicts (author's transl)].

Fifty drug addicts with parenteral heroin abuse and tentative diagnosis of acute hepatitis were examined by means of biochemical and serological tests and by liver biopsy. Diagnosis of acute hepatitis was confirmed in 23 patients. 12 patients were examined by liver biopsy a second time 2 months to 18 months later, 3 patients underwent liver biopsy three times. In 80% of the patients markers of hepatitis B (HBsAg, anti-HBs and anti-HBc) were found in the sera. There is some evidence of not only hepatitis B, but also hepatitis non-A, non-B in parenteral drug addicts leading to protracted forms of acute hepatitis and chronic hepatitis.

Adolescent↗
PubMed1980

[Gentamicin concentrations in cerebrospinal fluid of patients with inflamed and uninflamed meninges (author's transl)].

Determinations of gentamicin levels in serum and cerebrospinal fluid were performed in 11 tests of eight patients suffering from memingitis and in 18 tests of eight patients after neurosurgical operations. Neurosurgical operations had been performed in this group at least four days prior to testing. Only in four tests in neurosurgical patients were the gentamicin levels in CSF higher than the lowest measurable concentration of 0.4 mcg/ml, serum levels in this group ranged from below 0.4 mcg/ml up to 5.0 mcg/ml. No gentamicin level in CSF exceeded 1.5 mcg/ml. Gentamicin levels in CSF of patients with meningitis ranged from below 0.4 mcg/ml to 5.66 mcg/ml. This equals a CSF/serum ratio of 7.4-57.6%, mean 25.8%.

Gentamicins↗
PubMed1980

Complete separation by high performance liquid chromatography of metabolites of arachidonic acid from incubation with human and rabbit platelets.

Separation of all major cyclooxygenase and lipoxygenase metabolites of arachidonic acid were obtained by high performance liquid chromatography (HPLC). A C18 reverse-phase column was used in ion suppression mode to separate underivatized metabolites of arachidonic acid isolated from human and rabbit platelets. The metabolites were monitored by measuring radioactivity or ultraviolet light absorption at 192 nm (absorption by double bonds). Comparisons of TLC and HPLC separations demonstrated that the HPLC separation of metabolites of [1-14C]arachidonic acid was quantitative. HPLC also resolved several metabolites that were not detected by scanning of TLC separations.

Animals↗
PubMed1980

Nitrogen fixation by photosynthetic bacteria in lowland rice culture.

Propanil (3',4'-dichloropropionanilide) was a potent inhibitor of the nitrogenase activity of blue-green algae (cyanobacteria) in flooded soil, but the herbicide at comparable concentrations was not toxic to rice, protozoa, and nitrogen-fixing bacteria. Ethanol-amended flooded soils treated with propanil exhibited higher rates of nitrogenase activity than those not treated with the herbicide. The enhanced nitrogenase activity in propanil-treated soils was associated with a rise in the population of purple sulfur bacteria, especially of cells resembling Chromatium and Thiospirillum. By employing propanil and a means of excluding light from the floodwater to prevent the development of phototrophs during rice growth under lowland conditions, the relative activities of blue-green algae, photosynthetic bacteria, and the rhizosphere microflora were determined. The results suggest that the potential contribution of photosynthetic bacteria may be quite high.

Journal Article↗
PubMed1980

Desulfuration of dialkyl thiophosphoric acids by a pseudomonad.

A strain of Pseudomonas acidovorans used the organophosphorus pesticide breakdown products, ionic O,O-diethyl phosphorothioate and ionic O,O-diethyl phosphorodithioate, as sulfur sources. The growth yields from the thiophosphates and sulfate were 3.6 to 4.1 kg of protein per mol of sulfur. Elemental sulfur and sulfide also served as sulfur sources but gave lower growth yields.

Journal Article↗