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Biomedical subjects

T Ivanova

Publications and source records attributed to T Ivanova.

47 records · Page 3Linked to original sources
PubMed1984

Insulin receptor in cells of two transplanted tumors of mouse mammary gland.

Highly specific insulin receptors have been identified in the cells of two transplanted tumors of mammary gland in mice. The two tumors used for transplantation had morphological characteristics of an undifferentiated adenocarcinoma with a different growth rate. The specific binding was proportional to the number of tumor cells in the incubation mixture. Saturation of insulin binding sites was observed when the concentration of 125I-insulin increased over 5 X 10(-9) moles/l. The specificity of insulin binding to tumor cells was examined by means of competition with insulin derivatives: des-octapeptide insulin, tert-butyloxycarbonyl3-insulin (BOC3) and its des-octapeptide derivative were without any detectable activity in the concentration range used, i.e. from 5.5 X 10(-11) to 5.5 X 10(-5) moles/l. The data obtained from Scatchard's analysis of the binding were not linear and the affinity constants were similar for the cells of the two tumors. The total number of insulin receptor sites per cell, estimated by linear regression analysis, were higher for the cells isolated from the slow-growing tumor as compared to that of cells isolated from the fast-growing tumor and a lactating mammary gland. These results point to the possibility that the growth of mammary tumors could be under insulin regulation via insulin receptors.

Animals↗
PubMed1983

Synchronization of movement-related cerebral potentials for averaging.

A software-oriented technique is proposed for synchronization of the individual movement-related cerebral potentials on the basis of the first derivative of the mechanogram. All procedures are computer performed using neither trigger device nor time-reverse averaging later on. The main advantages of the technique over the trigger approach are demonstrated when determining onset of both commencement and termination of the sustained contraction. Besides the objectivity and high accuracy, the proposed technique gives an additional possibility to determine movement parameters together with cerebral potential characteristics and to sort out the movement-related EEG records in greater details.

Brain↗
PubMed1976

Alpha-fetoprotein in the serum of patients with neoplasms of the gastrointestinal tract.

Serum alpha-fetoprotein was estimated in 61 patients with neoplasms of the gastrointestinal tract, 29 healthy controls and 10 pregnant women. Almost half ot the patients had increased values of alpha-fetoprotein and no parellelism between alpha-fetoprotein and liver metastasis was found. Decreasing of the alpha-fetoprotein during the postoperative period could be considered a sign for a total removal of the tumor, and, on the contrary -- increasing of alpha-fetoprotein -- for a recurrence.

Adult↗
PubMedDate not supplied

Adaptive environmental control for optimal results during plant microgravity experiments.

The SVET Space Greenhouse (SG)--the first and the only automated plant growth facility onboard the MIR Space Station in the period 1990-2000 was developed on a Russian-Bulgarian Project in the 80s. The aim was to study plant growth under microgravity in order to include plants as a link of future Biological Life Support Systems for the long-term manned space missions. An American developed Gas Exchange Measurement System (GEMS) was added to the existing SVET SG equipment in 1995 to monitor more environmental and physiological parameters. A lot of long-duration plant flight experiments were carried out in the SVET+GEMS. They led to significant results in the Fundamental Gravitational Biology field--second-generation wheat seeds were produced in the conditions of microgravity. The new International Space Station (ISS) will provide a perfect opportunity for conducting full life cycle plant experiments in microgravity, including measurement of more vital plant parameters, during the next 15-20 years. Nowadays plant growth facilities for scientific research based on the SVET SG functional principles are developed for the ISS by different countries (Russia, USA, Italy, Japan, etc.). A new Concept for an advanced SVET-3 Space Greenhouse for the ISS, based on the Bulgarian experience and "know-how" is described. The absolute and differential plant chamber air parameters and some plant physiological parameters are measured and processed in real time. Using the transpiration and photosynthesis measurement data the Control Unit evaluates the plant status and performs adaptive environmental control in order to provide the most favorable conditions for plant growth at every stage of plant development in experiments. A conceptual block-diagram of the SVET-3 SG is presented.

Brassica↗
PubMedDate not supplied

Estrogen: a multifunctional messenger to nigrostriatal dopaminergic neurons.

Gonadal steroids affect a wide variety of functions in the mammalian brain ranging from the regulation of neuroendocrine systems and the modulation of behavior to the stimulation of differentiation and plasticity of distinct neuronal populations and circuits. The last decades have also demonstrated that estrogen serves as a neuroprotective factor for distinct neurodegenerative disorders. Such neuroprotective effects of estrogen are most obvious for Parkinson's and Alzheimer's disease. Despite this knowledge, little is known about the mechanisms and cellular targets by that estrogen might elicit its protective influence. In the past, we have intensively studied the effects of estrogen on midbrain dopaminergic neurons which represent the most affected cell population during Parkinson's disease. These studies were mainly performed on developing dopaminergic cells and revealed that estrogen is an important regulator of plasticity and function of this neuronal phenotype. Precisely, we found that dopaminergic neurons are direct targets for estrogen and that estrogen stimulates neurite extension/branching and the expression of tyrosine hydroxylase, the key enzyme in dopamine synthesis. Together with other in vivo studies, we might draw the conclusion that estrogen is required for the plasticity and activity of the developing and adult nigrostriatal system. The presence of the estrogen-synthesizing enzyme aromatase within the nigrostriatal system further supports this idea. Surprisingly, estrogen effects on nigrostriatal cell function are not only transmitted by classical nuclear estrogen receptors but also depend on nonclassical estrogen actions mediated through putative membrane receptors coupled to diverse intracellular signaling cascades. In the future, it has to be elucidated whether nonclassical mechanisms besides genomic actions also contribute to estrogen-mediated neuroprotection in the adult CNS.

Animals↗