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Following cortisol binding to the specific glucocorticoid receptors of thymus cells at 37° (a process which takes about 7 min), there is a 5- to 10-min lag period before a cortisol effect can be observed on glucose 6-phosphate accumulation after a glucose pulse. Evidence is presented that during this period the signal initiated by cortisol binding traverses an irreversible, an actinomycin D-sensitive, and a temperature-sensitive step.
The irreversible step is shown by the fact that removal of cortisol from the glucocorticoid receptors (by displacement with cortexolone, a metabolically inactive glucocorticoid competitor, or by washing) well before any metabolic effect has appeared does not prevent the subsequent appearance of the cortisol effect.
The actinomycin D-sensitive step is shown by the fact that, whereas addition of actinomycin D to thymus cells together with cortisol prevents the cortisol effect from developing subsequently, addition of actinomycin D 5 min after cortisol does not prevent the cortisol effect. To produce these actions, actinomycin D must be used at 100 µg per ml. This same concentration is necessary to inhibit RNA synthesis rapidly in thymus cells by about 80%.
The temperature-sensitive step is shown by the fact that the duration of the lag period preceding the appearance of a cortisol effect increases markedly at temperatures below 37° to more than 120 min at 20°. The duration of the lag period at 37° can be shortened if cells are first incubated with cortisol at 20°.
The temperature dependence of the irreversible step is such that it cannot be identical with, but must precede, the temperature-dependent step. The actinomycin D-sensitive step may or may not be identical with one of the other two steps.
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Publication history
Published online: February 10, 1971
Received:
June 15,
1970
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© 1971 ASBMB. Currently published by Elsevier Inc; originally published by American Society for Biochemistry and Molecular Biology.
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