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pubmed:abstractText |
Tumor tissues obtained from two patients with the ectopic ACTH syndrome caused by medullary carcinoma of the thyroid and malignant epithelial thymoma were dispersed by tryptic digestion and mechanical agitation. Using the isolated cells, the effects of various agents on ACTH secretion and intracellular cAMP concentrations were studied. Addition of rat median eminence extract significantly stimulated ACTH secretion and increased levels of intracellular cAMP in both cell preparations, and a dose-response relationship appeared to exist between the dose of rat median eminence extract added and either ACTH secretion or intracellular cAMP formation in the thymic tumor cells. High concentrations of calcium also produced a marked ACTH secretion in both cases. In the thymic tumor cells, norepinephrine, serotonin, and TRH were found to be effective in increasing ACTH secretion and intracellular cAMP levels, whereas biogenic amines, hypothalamic hormones, and gastrointestinal hormones did not affect hormone secretion in the thyroid tumor cells. These results suggest that a corticortropin-releasing factor-like substance(s), as yet unspecified, may play some role in stimulating ectopic ACTH secretion by certain tumors, that both intracellular cAMP and Ca++ may be involved in ectopic hormone secretion, and that the inappropriate hormonal secretory responses of some tumors to a variety of stimuli might be mediated by altered membrane receptors of the neoplastic cells.
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