Interaction of adrenal hormones in the regulation of ornithine decarboxylase activity in the thymus and liver of rats
Prahlad, K. V.
M.S. (Master of Science)
Department of Biological Sciences
Enzymes; Liver; Adrenocortical hormones; Thymus
The activity of L-ornithine decarboxylase (E.C. 188.8.131.52, ODC), the initial enzyme in the polyamine biosynthetic pathway, is a sensitive index of growth and proliferation. This enzyme can act as an early indicator of DNA and RNA synthesis, mitotic stimulation and tumor promotion and has become a useful indicator of tissue responsiveness to a number of hormones. Adrenal hormones in particular have been studied for their effect on ODC activity in various tissues. Despite this considerable interest in the regulatory control of ODC activity by the adrenal hormones, to date, no studies involving the interactions of these hormones in such action have been reported. In the present study, the changes in ODC activity in the thymus and liver, two tissues where glucocorticoids exert opposite effects, were studied following acute and chronic administration of adrenal hormones, alone or in combination,to adrenalectomized rats. Also, adrenalectomized rats chronically treated with epinephrine and aldosterone were used in a time-course study to determine the effects of dexamethasone on the ODC activity in these two tissues. Also reported are the thymus weights and the thymic and hepatic protein content for each of the experimental groups. Earlier studies reporting that dexamethasone reduces thymic ODC activity while increasing hepati-c ODC activity were supported by this study. Aldosterone was also observed to lower thymic ODC activity while increasing hepatic ODC activity. On the other hand, epinephrine increased and decreased ODC activity in the thymus and liver respectively. An antagonism appeared to occur between these adrenocortical and adrenomedullary hormones since chronic administration of dexamethasone or aldosterone with epinephrine resulted in control levels of ODC. When aldosterone and epinephrine were chronically administered to adrenalectomized rats to study the-acute effects of dexamethasone, thymic ODC activity was maximally inhibited by 10 hours following hormone administration and returned to control levels by 65 hours. Hepatic ODC activity was maximally stimulated by 5 hours after hormone treatment and returned to control values by 10 hours. The results of this study confirm the divergent effects of dexamethasone on thymic and hepatic tissues, especially ODC. Also, for the first time, aldosterone and epinephrine have been implicated in the complex regulation of ODC activity in these two tissues.
Zahner, Scott L., "Interaction of adrenal hormones in the regulation of ornithine decarboxylase activity in the thymus and liver of rats" (1984). Graduate Research Theses & Dissertations. 3607.
vii, 61 pages
Northern Illinois University
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Bibliography: pages 27-29.