PubMed Health⌕ Search

Biomedical subjects

H Atlan

Publications and source records attributed to H Atlan.

84 records · Page 5Linked to original sources
PubMedDate not supplied

A mathematical analysis of the mortality kinetics of Drosophila melanogaster exposed to gamma radiation.

A mathematical model with nonlinear time-varying characteristics has been developed which describes the relationship between the kinetics of natural aging and radiation-induced delayed mortality. Based on this model, it appears that there is an immediate effect of radiation which is continuously, but nonlinearly, increasing in severity. Two phases appear in this variation, corresponding to the two phases (plateau and dying phase) of the mortality curves for control populations. Accordingly, S/E (survival time post-irradiation/further expectation of life) can best be interpreted as an increasing function during the plateau phase of normal mortality curves, which levels off during the ensuing dying phase.

Aging↗
PubMedDate not supplied

Effects of temperature on the life span, vitality and fine structure of Drosophila melanogaster.

The effects of temperature on the aging process have been investigated in approximately 3500 imagoes of male Drosophila melanogaster (Oregon R), with focus on the following parameters: mortality, O2 utilization, vitality (as expressed by negative geotaxis and mating) and fine structural alterations in the abdominal organs and brain. The data on mortality kinetics of flies maintained continuously at 18 degrees, 21 degrees, 27 degrees or 30 degrees C or exposed in succession to 21 degrees and 27 degrees C or vice versa support the concept that life span is temperature dependent. Moreover, these data, together with the increased O2 utilization and accelerated loss of vitality at 21 degrees C as compared with 18 degrees C, suggest that, in agreement with the rate-of-living theory proposed by Alpatov and Pearl in 1929, the flies are living faster at the higher temperature. Fine structural aging changes, like ribosomal loss in the Malpighian tubules and lipofuscin-ceroid accumulation in the midgut cells, seem to be more intense at 27 degrees and at 29 degrees C than at 21 degrees C. Also, the low vitality exhibited through their lives by flies kept at previous exposure through many generations) to 21 degrees C. Flies maintained at 29 degrees C showed a striking degeneration of the brain with an almost complete loss of the cytoplasmic organelles of the nerve cells. This electron microscopic finding lends support to the view that nervous tissue injury (perhaps induced by thermal denaturation of membrane lipoproteins) may play a crucial role in life shortening induced by relatively high temperatures.

Animals↗
PubMedDate not supplied

Thermodynamics of aging in Drosophila melanogaster.

The data on mortality kinetics and decline in functions reported in the preceding article are used to calculate temperature coefficients for the aging process(es) in Drosophila. Different values are found, according to the model chosen to account for the mortality kinetics. The respective implications of three equally suitable models are discussed. Thus, organization parameters on two different levels can be identified: rates of changes assumed to occur at the elementary molecular level, and redundancy factors at a more integrated level. Their temperature coefficients are compared with those of protein denaturations and lipid peroxidation pigment accumulation. It is suggested that elementary molecular processes responsible for aging can indeed be protein denaturations, whereas the known lipid peroxidation pigment accumulation is more likely to be a secondary effect, resulting from a failure of the overall cellular organization at a more integrated, supramolecular, level.

Aging↗
PubMedDate not supplied

Mechanisms of autoimmunity and AIDS: prospects for therapeutic intervention.

The network theory of autoimmunity is presented with recent experimental data relevant to the understanding of the pathogenesis of AIDS. Schematically, effector T cells specific for self-antigens exist normally, but their activity is modulated and prevented by networks of regulatory T cells. As a result of mimicry between molecular components of microorganisms and self-antigens, autoimmune disease can be triggered by specific foreign pathogens which alter the state of activity of the network from suppression to activation. Conversely, by a procedure known as T-cell vaccination, autologous effector T cells re-injected after in vitro stimulation and attenuation may alter the state of the network from an activation to a suppression. Numerous observations are reviewed that support the concept of autoimmune activity in the destruction of non-infected T4 cells. Such activity is presumed to be triggered by an antigen of viral origin, the most likely, but not the only one, being the envelope protein gp 120. Based on this hypothesis, a T-cell vaccination procedure against effector T cells responsible for autoimmunopathic activity in HIV-seropositive patients is proposed, similar to the one known from experimental study of autoimmunity and presently being tested in human autoimmune diseases. Its purpose would be to prevent T-cell loss and the onset of immunodeficiency disease in HIV-seropositive patients. Apart from its potential therapeutic value, this procedure will have use as a therapeutic test from which insight will be gained about the immunopathogenesis of AIDS.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Negative bone scans in impending tibial stress fractures. A report of three cases.

Three highly motivated military recruits who presented with tibial pain on exertion are reported. Their initial bone scan assessments to rule out stress fracture were normal, and the recruits were returned to demanding training. One month later, because of persistent and increasing tibial pain, they were rescanned and focal activity representative of tibial stress fractures was found in each case. Until now it has been assumed that a negative bone scan ruled out a stress fracture unequivocally. Our reported cases show that bone pain may in fact precede scintigraphic evidence of a stress fracture. Persistent and increasing bone pain during demanding physical activity, even in the presence of a prior normal bone scan, may represent stress fracture and repeat bone scan may be indicated.

Humans↗
PubMedDate not supplied

Scintigraphic evaluation of patients with thyroid carcinoma--therapeutic approaches.

The therapeutic approach to patients with differentiated thyroid carcinoma has become a major issue of controversy in the last decade. The major aspects are the surgical resection and adjuvant therapy, particularly the need for thyroid ablation following surgery. According to the risk group definition suggested by Cady in 1979, low risk patients may be subjected to lobectomy only, then placed on thyroxine treatment and followed clinically with thyroglobulin determination. High risk patients should undergo total thyroidectomy and 131I ablation. Follow-up should include thyroxine treatment and an annual whole body 131I scan. In the event of residual thyroid tissue or functional metastases, 131I treatment is to be given.

Adolescent↗
PubMedDate not supplied

Scintigraphic techniques in pre-operative localization of parathyroid adenoma.

Solitary parathyroid adenoma is the most common cause of primary hyperparathyroidism. It can be removed surgically with a 92-96% success rate without any pre-operative imaging procedures. However, imaging procedures may be of help in localization, thereby reducing operative morbidity, and in the detection of ectopic adenomas. The decision to undertake surgical exploration should not be based on these procedures because of their low sensitivity and limited specificity when used alone, but rather on an established biochemical diagnosis of hyperparathyroidism.

Adenoma↗
PubMedDate not supplied

Multiple stress fractures. A longitudinal study of a soldier with 13 lesions.

A highly motivated 18-year-old man continued vigorous military training in spite of the presence of 11 stress fractures and subsequently developed two additional stress fractures. Scintigraphy over 27 weeks illustrated simultaneous regression and progression in his individual multiple foci. When stress fracture foci were not in anatomic locations prone to evolve to gross fractures, healing occurred despite vigorous activities and pain.

Adolescent↗