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Biomedical subjects

A Leonard

Publications and source records attributed to A Leonard.

At least 73 records · Page 4Linked to original sources
PubMed1981

Mutagenicity of n-nitrosodiethanolamine and its acetyl derivatives.

The mutagenicity of N-nitrosodiethanolamine and its mono- and di-acetyl derivatives was tested in the S. typhimurium test system, in cytogenetic studies and in the micronucleus test. N-nitrosodiethanolamine had no mutagenic effects towards several strains of S. typhimurium either in the absence or in the presence of metabolic activating systems. Its diacetyl derivative exerted mutagenic effects towards the S. typhimurium strains TA1530 and TA100. Neither compound increased significantly the nubmer of chromosomal aberrations or of micronuclei in mice.

Animals↗
PubMed1981

Mutagenicity of acrylonitrile in mouse.

The capacity of acrylonitrile (ACN) to produce chromosome aberrations in mammals was studied in somatic and germ cells of male NMRI mice. Induction of chromosome aberrations was followed in bone marrow cells 6, 18, 24, 48 and 72 h after an i.p. injection of 20 or 30 mg/kg acrylonitrile, and polychromatic erythrocytes were examined for the presence of micronuclei 24, 30 and 48 h after injection. The dominant lethal test served to detect chromosome aberrations in meiotic and postmeiotic male germ cells. All the tests utilized yielded negative results, so that it may be concluded that acute treatment with acrylonitrile has no clastogenic effects on male mouse cells in vivo.

Acrylonitrile↗
PubMed1980

Lymphocyte lifetime in the rabbit measured by the decline in radiation-induced chromosome damage.

The life span of rabbit lymphocytes carrying radiation-induced chromosome aberrations has been studied by following the decline in aberration frequency as a function of the time after irradiation. Female rabbits were given a whole body X-ray dose of 300 rad. The day before exposure and at 2 hours, 14, 28, 42, 56, 84, 140, 250 and 500 days thereafter, blood samples were taken from a marginal ear vein of each animal. A plot of log abnormalities against time suggests an exponential decline for dicentrics and fragments up to 140 days, the half time for dicentrics and fragments being 70 and 46 days respectively. The results of the present investigation thus demonstrate that because of their shorter life span, in vivo observations on aberrations in rabbit lymphocytes are not suitable for extrapolation of information on chronic exposure to man.

Animals↗
PubMed1980

Internal medicine.

Explore the source record for details and available documents.

Attitude of Health Personnel↗
PubMed1980

[Methods used for the in vivo study of the mutagenic properties of chemical substances].

Since man is much more closely related to other mammals than to bacteria fungi, plants or Drosophila, information obtained from mammals have obviously a much greater relevance to man than those from lower animals. Only the intact mammal can be utilized to obtain information on pharmacokinetic aspects such as absorption, elimination, biotransformation both inside and outside the target cells. Most mammalian assay systems employed for routine screening of mutagenic action rely on the detection of chromosome breaks in bone marrow, testis or in the dominant lethal test. In conclusion, it can be stated that in all cases, on should be guided by the consideration that no genetic risk whatsoever is acceptable when the mutagenic compound presents no clear benefit or when an alternative is available. Is this not the case, risks must be carefully balanced against possible benefits of the application of the mutagenic agent in question.

Animals↗
PubMed1980

[Repair of chromosomal aberrations in a human peripheral blood lymphocyte system after single and split-dose x-irradiation].

Whole human peripheral blood was exposed either acutely to 125 or 250 R X-rays or in fractions to 125+125 R X-rays at varying cell cycle times, namely, 0, 2, 4, 6, 8, 12, 16, 24, 30, 40 or 45 hours after culture initiation. Well spread metaphase chromosomes were examined for the following types of structural chromosome aberrations: dicentrics, rings, interstitial deletions, symetrical translocations, chromatid and chromosome fragments. Most noteworthy were found to be the polycentric + ring data. With acute radiation given at any of the times over the presynthetic period, the yields of these aberrations were consistently within the range of 17-20% for the 125 R dose and 66-73% for 250 R. For either acute dose given at later times, the aberration yields decreased to fall to 1% by the end of the synthetic period. With fractionated 125+125 R exposures the following rates were obtained: irradiation at 2 hr time in culture, 44.15%; 4 hr, 50.82%; 6 hr, 55.16%; 8 hr, 58,32% (peak rate): 12 hr, 55.48%. The downward trend persisted to the end of the presynthetic period and during the synthetic period. Statistical data treatment indicated acute and fractionated exposures to differ significantly in production of polycentric+ring yields, as well as in those of other aberration types and total breakage per cell. It may be concluded from our findings that the time course of repair processes is of an undulated pattern, with peak intensity within the first hours of the presynthetic period, a fall by 8 hr and a following renewed rise; repair was found to occur nearly to the end of the synthetic period.

Cell Cycle↗
PubMed1980

[Chromosome aberrations in human peripheral blood lymphocytes after single and split-dose x-irradiation].

Effects of single exposures to 125 or 250 R and those of fractionated irradiations of 2.125 R on human lymphocytes were studied upon the chromosome aberration yields in blood maintained in a refrigerator at 5 degrees C for the intervals between the irradiations. Single irradiations succeeded venepuncture; the same holds for the first dose from the fractionated one, while he second was delivered at one of the following intervals: 2.8 or 24 hours. Immediately after completion of irradiation, blood was cultured to obtain metaphase slides for cytogenetic analysis. No repair processes were observed in the hereditary cell structures of fractionatedly irradiated blood if it was maintained at 5 degrees C for the intervals between irradiations. More chromosomes fragments, interstitial deletions, aberrant cells, and breakage of cells were scored, on the opposite, in fractionatedly irradiated blood, which was stored for 24 hours. These were even with high statistically significant differences when compared with singly exposed cells to the same doses. This effect was likely to be due to blood stirage.

Chromosome Aberrations↗
PubMed1979

Relation between cell cycle and yield of aberrations observed in irradiated human lymphocytes.

The bromodeoxyuridine-Giemsa technique has been used to study systematically the incidence of cells in first or subsequent mitoses at different fixation times of human lymphocyte control cultures as well as the influence of ionizing radiations on cell kinetics. Second divisions appear (3%) in cultures harvested 48 h after initiation. In 72 h cultures 40% of the dividing cells are in second and 33% in third division. Administration of 200 rads of X-rays before PHA stimulation results in a mitotic delay but does not increase the incidence of SCE. The yield of dicentrics after an exposure to 200 rads was the same for all cells in first mitosis regardless of fixation time. These results demonstrate that there is no evidence for the existence of sensitive subpopulations that could be distinguished by the time of the first mitotic division following stimulation.

Cell Cycle↗
PubMed1979

Learning style in a primary care internal medicine residency program.

Individual differences in learning style should be one factor that is considered in medical education program planning and instruction, and this can be accomplished by using Kolb's learning style inventory (LSI) in a primary care internal medicine residency program. Case accounts are presented to suggest how the LSI can be used to enrich teaching-learning encounters. To our knowledge, these case accounts are the first reports of an important use of knowledge about learning style, obtained through instruments such as the LSI. Other educational applications are suggested with respect to evaluation formats and choice of instructional methods.

Faculty, Medical↗
PubMed1979

[Utilization of chromosomal markers in cancer research].

The mouse is an unsuitable species for cytogenetical studies to the extent that it has 40 acrocentric chromosomes and the only criterion which could be used to differentiate them is size. We envisaged using in the case of cell grafts donors or recipients of different sex. This technique has, however, been used to a limited extent. Among the other markers which have been utilized, T6T6 of CBA mice must be mentioned. The discovery in 1966 by Léonard and Dekundt of the presence in AKR mice of fusions of the Robertson type (between chromosomes 6 and 15) has generated new interest in experimental work based on the utilisation of chromosome markers. Being interested in the mechanisms of radio-induced leukemia, the authors described how they have introduced the chromosome marker of AKR mice into the C57B1 strain which is very sensitive to the induction of radio-induced leukemias.

Animals↗
PubMed1978

[Effect of age on the sensitivity of mouse spermatogonia to mutagenic action].

Male BALB/c mice were whole body exposed to 0, 100, 200 or 300 R of X-rays or were given an i.p. injection of 5 mg/kg of thio-TEPA at 3 months or at 12 months of age. One hundred days after treatment the testes were examined for the presence of reciprocal translocations induced in spermatogonia and detectable in the dividing spermatocytes. Our results show that ages does not influence the yield of scorable chromosome rearrangements.

Aging↗
PubMed1977

Plasma hormone levels in normal and lead-treated pregnant mice.

Dietary lead (0.5%) was given to mice which, after mating, exhibited a vaginal plug. Estradiol, progesterone and prostaglandins E and F 2 alpha were determined in the plasma by radioimmuno assay at different times thereafter. The increase in estradiol and decrease in prostaglandins prior implantation are not greatly altered by lead treatment, whereas the subsequent increase in progesterone and later in estradiol is abolished. It is concluded that the lower number of pregnancies seen in lead-treated mothers is due to a maternal hormonal imbalance caused by lead.

Animals↗