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Biomedical subjects

M Alexander

Publications and source records attributed to M Alexander.

At least 271 records · Page 15Linked to original sources
PubMed1980

Microbial metabolism of N-nitrosodiethanolamine in lake water and sewage.

The carcinogenic nitrosamine, N-nitrosodiethanolamine (NDElA), was degraded in samples of sewage and two lake waters, and microorganisms were responsible for the transformation. However, the rate of NDElA disappearance was slow. In the samples of lake water, the rate and extent of NDElA metabolism varied with the time of year, and no disappearance occurred in samples taken in winter. The products formed from NDEIA were persistent in lake water. In sewage, no seasonal effect on the microbial conversion was evident, and the products of metabolism were slowly mineralized. NDElA is apparently converted to the same organic products in samples of all three environments. Although the products were not identified, the data suggest that they were modified dimers of NDElA.

Bacteria↗
PubMed1980

Evidence Suggesting Protozoan Predation on Rhizobium Associated with Germinating Seeds and in the Rhizosphere of Beans (Phaseolus vulgaris L.).

Changes in populations of microorganisms around germinating bean (Phaseolus vulgaris L.) seeds, in the rhizosphere of bean, and in a model rhizosphere were studied. Strains of Rhizobium phaseoli that were resistant to streptomycin and thiram were used, and as few as 300 R. phaseoli cells per g of soil could be enumerated with a selective medium that was devised. A direct role was not evident for bacterial competitors, lytic bacteria, antibiotic-producing microorganisms, bacteriophages, and Bdellovibrio in the suppression of R. phaseoli around germinating seeds and in the rhizosphere. Protozoa increased in numbers in the soil upon planting of the seeds. The extent of colonization of soil by R. phaseoli was inversely related to the presence of large numbers of bacteria and protozoa. Colonization of R. phaseoli was improved upon suppression of protozoa with thiram and also when the soil was amended with other protozoan inhibitors and mannitol to simulate seed and root exudation. The data support the view that the decrease in numbers of R. phaseoli is caused by an increase in protozoan predation, the protozoa increasing in number because they prey on bacteria that proliferate by using seed and root exudates as nutrients.

Journal Article↗
PubMed1980

Effect of rice plants on nitrogenase activity of flooded soils.

In samples of flooded soil containing blue-green algae (cyanobacteria), the presence of rice plants did not influence the nitrogenase activity of the algae. Nitrogenase activity of heterotrophic bacteria was enhanced by the presence of rice plants, but this activity was not affected by changes in plant density. The rate of nitrogen fixation in the rhizosphere, however, varied significantly among the 16 rice varieties tested. A simple method was devised to test the nitrogen-fixing activity in the root zone of rice varieties, and data were obtained showing marked differences in the activities of the 16 varieties. In tests of two varieties with dissimilar rates of nitrogen fixation in their rhizospheres, the variety which had the greater root weight and lesser shoot weight and which supported greater methane formation had the greater nitrogenase activity.

Journal Article↗
PubMed1980

Evidence for cometabolism in sewage.

A procedure was developed to demonstrate cometabolism in models of natural ecosystems. The procedure involves showing the formation of metabolic products in high yield and the lack of incorporation of substrate carbon into cellular constituents. Samples of four C-labeled herbicides (trifluralin, profluralin, fluchloralin, and nitrofen) were incubated with sewage aerobically and under discontinuous anaerobiosis for 88 days, and fresh sewage was added at intervals. Products were formed from each of the herbicides in nonsterile, but not in sterile, sewage. The yield of recovered products reached 87% for profluralin and more than 90% for fluchloralin and trifluralin, and the number of products ranged from 6 for nitrofen to 12 for fluchloralin. Concentrating the sewage microflora 40-fold greatly enhanced the rate of conversion. None of the radioactivity from the herbicide entered the nucleoside pool of the sewage microflora. The lack of incorporation of substrate carbon into cells and the almost stoichiometric conversion of the substrate to organic products indicate that members of the microbial community were cometabolizing the test compounds.

Journal Article↗
PubMed1980

Hyperalimentation and cancer.

Over an 8-year period, 106 patients with cancer who were major operative risks received intravenous hyperalimentation (IVH). All were malnourished, had gastrointestinal obstruction or had postoperative complications such as fistulas, evisceration or intra-abdominal sepsis, which left IVH as the only means of achieving anabolism. When IVH was started preoperatively and continued postoperatively (34 patients), no deaths or major complications occurred. When IVH was first started after serious complications had occurred (62 patients), the incidence of recovery was high; the mortality was 17.7%. When IVH was given to cachectic patients whose cancer was inoperable to enable them to tolerate radiotherapy or chemotherapy (10 patients), the mortality was 40.0%. Although this last group is small, IVH is worthwhile in selected patients in whom good palliation life can be obtained. With careful IVH and improvement in the quality of technique, the risk of sepsis was no greater than in patients without cancer.

Adult↗
PubMed1980

Relationships between cholesterol gallstones, biliary function, and plasma lipoproteins in squirrel monkeys.

We used squirrel monkeys (Saimiri sciureus) as models to investigate human sex differences in susceptibility to cholesterol gallstones, biliary function, and plasma lipoproteins. Cholesterol gallstones developed in a large proportion of intact and gonadectomized male and female Brazilian monkeys maintained on a lithogenic diet, but male Bolivian monkeys were completely resistant. Although the gallbladder bile of nearly all monkeys was saturated with cholesterol, the bile of the Bolivian monkeys had a much greater concentration of total lipids (cholesteriol + phospholipid + bile acids) than did bile of the other groups. The male Bolivian monkeys had the highest percentage of gallbladder bile acids as chenodeoxycholic and the lowest as deoxycholic acids. They also had larger total body pools of cholic and chenodeoxycholic acids than any other group. The lithogenic index of all Brazilian squirrel monkeys with gallstones was greater than that of all Brazilian monkeys that were free of stones. The level of HDLs was much lower in the plasma of Bolivian monkeys than in that of any group of Brazilian monkeys, and the differences were restricted to the HDL2 subfraction. Addition of cholesterol (0.9 mg/Kcal) to the regular semipurified diet containing butter resulted in elevations in the LDLs of all groups and a change in the relative compositions of HDL and LDL (a higher percentage of cholesterol and lower percentage of protein). The occurrence of low plasma HDL2 levels in a population of squirrel monkeys resistant to cholesterol gallstones is consistent with the suggested role of that fraction in net transport of cholesterol to the bile.

Animals↗
PubMed1979

Sexual behavior in male rhesus monkeys elicited by electrical stimulation of preoptic and hypothalamic areas.

Electrical stimulation of the preoptic area, lateral hypothalamus or dorsomedial nucleus of the hypothalamus (DMH) has produced sexual behavioral responses in 11 male rhesus monkeys. At a short latency following the onset of each train of stimulation, the stimulated males would mount estrogen-treated, receptive females. Quantitative measures of the elicited sexual behavior, in 4 males, were applied to describe differences between the effect of preoptic and DMH stimulation on male sexual performance. As compared to spontaneous sexual activity, stimulation of the DMH produced mounts of longer duration, with more thrusts per mount, higher thrusting rates and a greater number of ejaculations per test session; refractory periods between successive ejaculatory episodes were shortened as a result of stimulation-induced mounting behavior. Preoptic stimulation also induced mounts of longer than normal duration characterized by a slightly increased number of thrusts per mount. In contrast to DMH stimulus effects, however, thrusting rate was decreased significantly by preoptic stimulation and ejaculation did not occur even after multiple stimulus-induced mounts. Penile erections were elicited by stimulation of the anterior hypothalamus, ventromedial nucleus and the posterior hypothalamus in socially isolated or restrained males; however, stimulation of these same sites was ineffective for provoking sexual behavioral responses when tests were performed while the males were paired with receptive females.

Animals↗
PubMed1979

HLA-antigens in systemic lupus erythematosus (SLE).

Histocompatibility antigens were determined in 27 patients with SLE and 283 normal blood donors. HLA-B8 was significantly increased in patients with SLE (59.3%) as compared to the controls (20.5%, Pc less than 0.005). The relative risk for HLA-B8 was 5.64. No correlation could be demonstrated to specific organ involvement, immunopathological data, age of onset or prognosis.

Adolescent↗