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Biomedical subjects

G V Levin

Publications and source records attributed to G V Levin.

At least 19 recordsLinked to original sources
PubMed1999

Disposition of D-[U-14C]tagatose in the rat.

The purpose of this experiment was to determine the disposition of D-tagatose, under development as a low-calorie sweetener, in conventional and germ-free male rats. One group of conventional rats was fed a diet containing D-tagatose (100 g/kg) mixed with the nonpurified diet (900 g/kg) for 28 days. Then, [U-14C]-labeled D-tagatose was administered as a single dose (approximately 220-380 kBq) to 4 of these adapted rats, as well as to 15 conventional and germ-free rats with no prior exposure (i.e., unadapted) to D-tagatose. Eleven of the 19 dosed animals (4 adapted conventional, 3 unadapted conventional and 2 unadapted germ-free, all dosed orally, plus 2 unadapted conventional dosed intravenously) were placed in metabolism chambers and samples of CO2, urine, and feces taken at regular intervals. At termination, a complete material balance was obtained based on the recovery of 14C. Over the 6-h digestive period, D-tagatose was metabolized to release 39.9 and 13.9% of the oral dose as CO2 in the adapted conventional rats and in the unadapted germ-free rats, respectively. Total releases approximated 68 and 22%, respectively. The difference in CO2 evolution is ascribed to microbial fermentation of D-tagatose in the gut of the conventional rats. The role of adaptation was confirmed by finding 93% less D-tagatose in the feces of the adapted conventional rat than in the feces of the unadapted conventional rat. The intestinal absorption of D-tagatose in the rat is estimated to be 20%. The results demonstrate that D-tagatose is metabolized primarily by microorganisms in the gut of the rat, with an upper limit between 15 and 20% of oral dose metabolized by the host.

Administration, Oral↗
PubMed1999

Effects of acute and repeated oral doses of D-tagatose on plasma uric acid in normal and diabetic humans.

D-tagatose, a stereoisomer of D-fructose, is a naturally occurring ketohexose proposed for use as a low-calorie bulk sweetener. Ingested D-tagatose appears to be poorly absorbed. The absorbed portion is metabolized in the liver by a pathway similar to that of D-fructose. The main purpose of this study was to determine if acute or repeated oral doses of D-tagatose would cause elevations in plasma uric acid (as is seen with fructose) in normal humans and Type 2 diabetics. In addition, effects of subchronic D-tagatose ingestion on fasting plasma phosphorus, magnesium, lipids, and glucose homeostasis were studied. Eight normal subjects and eight subjects with Type 2 diabetes participated in this two-phase study. Each group was comprised of four males and four females. In the first phase, all subjects were given separate 75 g 3-h oral glucose and D-tagatose tolerance tests. Uric acid, phosphorus, and magnesium were determined in blood samples collected from each subject at 0, 30, 60, 120, and 180 min after dose. In the 8-week phase of the study, the normals were randomly placed into two groups which received 75 g of either D-tagatose or sucrose (25 g with each meal) daily for 8 weeks. The diabetics were randomized into two groups which received either 75 g D-tagatose or no supplements of sugar daily for 8 weeks. Uric acid, phosphorus, magnesium, lipids, glycosylated hemoglobin, glucose, and insulin were determined in fasting blood plasma of all subjects at baseline (time zero) and biweekly over the 8 weeks. The 8-week test did not demonstrate an increase in fasting plasma uric acid in response to the daily intake of D-tagatose. However, a transient increase of plasma uric acid levels was observed after single doses of 75 g of D-tagatose in the tolerance test. Plasma uric acid levels were found to rise and peak at 60 min after such dosing. No clinical relevance was attributed to this treatment-related effect because excursions of plasma uric acid levels above the normal range were small and were of short duration. Consistent with earlier observations on fructose, the increase of plasma uric acid was associated with a slight decrease of plasma phosphorus and a slight increase of magnesium. The daily ingestion of D-tagatose for 8 weeks had no effect on fasting plasma magnesium, phosphorus, cholesterol, triglycerides, glycosylated hemoglobin, glucose, and insulin levels. The ingestion of three 25-g doses per day for a period of 8 weeks resulted in varying amounts of flatulence in seven of the eight subjects, and some degree of diarrhea in six subjects. D-tagatose holds promise as a sweetener with no adverse clinical effects observed in these studies.

Blood Pressure↗
PubMed1995

Sugar substitutes: their energy values, bulk characteristics, and potential health benefits.

Restriction of dietary energy extends life and reduces incidences of disease in animals. These benefits would likely extend to humans. However, diet restriction in animals imposes reductions of 30-50% in food intake, which is probably unacceptable to humans. Low-energy sweeteners used in beverages offer minor reductions in energy intake. However, they lack the bulk required for baked goods and other sugar-rich foods. Full-bulk sweeteners providing about one-half the energy of sugar are under development for such uses. Laxation limits their acceptable dose. Even within such limitations, they can help achieve the health benefits for humans indicated by diet restriction. D-Tagatose, a new candidate sweetener, is nearly as sweet as sucrose and has the bulk of sucrose, yet provides zero available energy. We discuss its potential contribution to human diet restriction along with its specific effect in delaying the aging effects of glycosylation.

Animals↗
PubMed1990

[Specificity of histological interrelations of cardial glands of the esophagus with its multi-layer lining].

Bioptates obtained from 163 mature persons have been studied, using spiral sections. When the conditions of functioning are altered (at the gastro-esophageal reflux) the organ's integument can destroy, but the defects formed in the lining are covered with a simple cylinder epithelium of the cardial glands. A connection between Barrett's syndrome in the esophagus with its cardial gland is demonstrated. The most widely distributed histological forms of Barrett's esophagus are described.

Adult↗
PubMed1985

[Structure of the cardial glands of the human esophagus].

The inferior and superior cardial glands of the esophageal wall have been studied in 156 mature persons (67 women and 89 men). The inferior cardial glands are represented as glandular brackets with predominance of secretory parts of the tubular form. In the superior cardial glands acini in the alveolar-tubular form are well developed. Glandular epithelium in terminal parts is polymorphic. In most of the acini it is cylindrical and sometimes cuboidal. The ducts of the cardial glands have a peculiar structure. Their simple cylindrical epithelium joins with multilayered esophageal epithelium. In the area of the ducts the multilayered esophageal epithelium often becomes thin and exfoliates, and this area of the mucous membrane is covered with cylindrical glandular epithelium.

Epithelial Cells↗
PubMed1979

Completion of the Viking labeled release experiment on Mars.

The final Labeled Release (LR) cycle on each Viking lander tested a surface sample that had been stored for several months at approximately 10 degrees C prior to the onset of the active sequence. At each lander site, activity was strongly diminished. This thermal sensitivity of the active agent on the surface of Mars is consistent with a biological explanation of the LR experiment. At the end of one of these cycles, the incubation mixture was heated to 50 degrees C to release any radioactive gas trapped in the sample matrix. The results suggest that more than one carbon substrate is involved in the LR reaction on Mars. The thermal data from the stored samples, coupled with data from previous cycles, have formed the basis for evaluation of the thermal decomposition of the Mars active agent. The slope of the resulting Arrhenius plot has been used to test the fit of other flight data and to calculate the activation energy for thermal decomposition of the Mars agent. The results and their interpretation still leave unresolved the question of whether the Mars LR data were generated by biological or chemical activity.

Carbon Radioisotopes↗
PubMed1979

Laboratory simulations of the Viking labeled release experiment: kinetics following second nutrient injection and the nature of the gaseous end product.

Injection of 14C-labeled nutrient onto Mars soil produced an evolution of 14C gas in the Viking Labeled Release (LR) experiment. However, a second injection of nutrient seven days later was followed by an abrupt diminution of the amount of radioactive gas in the test cell. Simulation experiments performed in the LR Test Standards Module (TSM) have yielded a plausible explanation for this diminution. Radioactive carbon gases were injected into the TSM test cell in the presence and absence of two Mars analog soils. After equilibration, water was injected and its effect observed. The results indicate that the flight data following second nutrient injection can be explained on a physico-chemical basis involving a carbon dioxide/water/soil equilibrium in the test cell. The results also suggest that the gaseous end product of the Labeled Release reaction on Mars is more likely carbon dioxide than carbon monoxide.

Carbon Radioisotopes↗
PubMed1977

Life on Mars? The Viking labeled release experiment.

Viking radiorespirometry ("Labeled Release" [LR]) experiments conducted on surface material obtained at two sites on Mars have produced results which on Earth would clearly establish the presence of microbial activity in the soil. However, two factors on Mars keep the question open. First, the intense UV flux striking Mars has given rise to several theories postulating the production of highly oxidative compounds. Such compounds might be responsible for the observed results. Second, the molecular analysis experiment has not found organic matter in the Mars surface material, and therefore, does not support the presence of roganisms. However, sensitivity limitations of the organic analysis instrument could permit as many as one million terrestrial type bacteria to go undetected. Terrestrial experiments with UV irradiation of Mars Analog Soil did not produce Mars type LR results. Gamma irradiation of silica gel did produce positive results, but not mimicking those on Mars. The life question remains open.

Carbon↗
PubMed1977

Identification of Leishmania spp. by radiorespirometry.

Preliminary investigation of the application of radiorespirometric technic to protozoan parasites of man indicates a potential for rapid identification. This technic, developed for identification of bacteria, was modified for use with culture forms of Leishmania. Five strains of Leishmania were compared: 2 of L. donovani, 2S and K; L. brasilensis, 2936 and B; and 1 of L. tropica, A. Consisent and rapid (approximately 2 hr) identification was obtained by the radiorespirometric procedure. A computer-type analysis of the radiorespirometric profiles of the 5 strains permitted correct identification of each isolate at the strain level 100% of the time. This technic offers several advantages over many current procedures for identification of protozoan parasites: (A) It is simple, rapid and highly reproducible, (B) Since it does not rely on visual or spectrophotometric determination, it may be conducted in the presence of optically complex substances. (C) It requires relatively low numbers of organisms (approximately 2 x 10(5)/14C-labeled substrate). (D) It is based on differential enzymic activity between species and strains of organisms and therefore, ultimately, on inherent genetic determinates of the parasites. (E) Further development of the procedure and accumulation of a data reference "bank" would allow automation of most of the identification process.

Animals↗
PubMed1973

Method for radiorespirometric detection of bacteria in pure culture and in blood.

Methods are described for the detection of low numbers of bacteria by monitoring (14)CO(2) evolved from (14)C-labeled substrates. Cell suspensions are filtered with membrane filters, and the filter is then moistened with 0.1 ml of labeled medium in a small, closed apparatus. Evolved (14)CO(2) is collected with Ba(OH)(2)-moistened filter pads and assayed with conventional radioactivity counting equipment. The kinetics of (14)CO(2) evolution are shown for several species of bacteria. Fewer than 100 colony-forming units of most species tested were detected in 2 h or less. Bacteria were inoculated into blood and the mixture was treated to lyse the blood cells. The suspension ws filtered and the filter was placed in a small volume of labeled medium. The evolved (14)CO(2) was trapped and counted. A key development in the methodology was finding that an aqueous solution of Rhyozyme and Triton X-100 produced lysis of blood but was not detrimental to bacteria.

Bacteria↗