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The effects of whole-body irradiation on thyroid hormones and metabolism in rats
Başlık:
The effects of whole-body irradiation on thyroid hormones and metabolism in rats
Yazar:
Gray, William Maxwell, author.
ISBN:
9780438059573
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (233 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Advisors: J. S. Orr.
Özet:
The work described in this thesis was carried out in an attempt to clarify the metabolic changes occurring after irradiation of living tissue. The animals used were rats and a single whole-body dose of radiation was employed because of the ease of application and the reproducibility of such a regime. The major part of the work was an investigation into the changes in the serum levels and kinetics of the thyroid hormones produced by whole-body irradiation, in an attempt to ascertain whether the thyroid system plays an active role in the response to radiation. Preliminary experiments with low radiation doses indicated that it would be necessary to use doses around the threshold of lethality from the bone-marrow and gastro-intestinal syndromes in order to invoke a significant response. In the main experiments, serum hormone concentrations were measured by radioimmunoassay and kinetic parameters obtained by observing the disappearance of I131-labelled hormone administered during the pre-irradiation period and I125-labelled hormone injected at 24 hours or 48 hours after the irradiation. Care was taken to make the conditions for the irradiated and control groups as similar as possible, particularly by pair feeding the control groups. The results of these experiments indicated that it is necessary to give careful consideration to the effects of radiation-induced anorexia in order to answer the question of whether the thyroid system plays an active role in the response to irradiation. A dose of 800 rads caused a sustained reduction in serum T4 levels, with the pair fed control group showing a similar although smaller change. The kinetic results indicated that, in the control group, the early reduction in T4 was caused by decreased production, whereas, in the irradiated group, it was due to diversion of the hormone from the blood to the tissues. The total effects of radiation on the test rats (including the effects of radiation-induced anorexia) were compared with the effect of diminished food intake alone on the control rats, with special attention being paid to the relation of the kinetic changes to the duration of diminished food intake; it then became apparent that the onset of two of the effects of partial starvation alone (reduced disappearance rate of T4 from the serum and reduced production of T4) was delayed by 24 to 48 hours in the irradiated rats, A similar pattern for levels and kinetics was observed following 750 rads. These results were interpreted as indicating that, during the first few days after whole-body irradiation, the thyroid system plays an active role in the response to the radiation. It is not possible at present to conclude whether this active involvement is concerned mainly with the elaboration of radiation-induced catabolism, or with the repair of damaged tissue, or whether the thyroid hormones are involved equally in both of these processes. It had also been intended to investigate the effects of radiation on the thyroxine-binding proteins in rat serum, but no satisfactory studies could be carried out on this topic because a suitable assay for the: proteins could not be developed. However, measurements were made of the changes in serum IgG and albumin levels produced by radiation; these confirmed the previously observed reduction in albumin concentration following irradiation, and showed that it can not be attributed to radiation-induced inanition. Finally, pilot studies were carried out into the possibility of using a recently constructed small animal calorimeter to investigate the effect of radiation on metabolic rate. Initial experiments on the influence of altered thyroid status on metabolic rate led to a greater appreciation of the complexities of temperature regulation in the rate Following these studies, calorimetric measurements were made on a rat irradiated to 500 rads; it was found that the metabolic rate dropped slightly following the irradiation, but this v/as probably the result of reduced movement of the rat inside the calorimeter. These pilot studies clarified several methodological details which it will be important to observe in any future attempts to correlate thyroid status with calorimetric measurements.
Notlar:
School code: 0547
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684734.1) | 684734-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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