Pituitary Nuclear Retention of Dexamethasone and ACTH Biosynthesis

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Abstract
The possible binding of 3H-dexamethasone (Dx)to the anterior pituitary and the effect of the steroid on neo-synthesis and release of ACTH of glands incubated with crude CRF extracts were examined. Neosynthesis of ACTH was determined by immunoprecipitation after incorporation of 14C-phenylalanine into the peptide. Using a cell-free system, 3H-Dx was shown to combine with the nuclear fraction of the pituitary. Short-term in vitro pre-treatment with Dx suppressed the CRF-induced hormonal release, but did not alter ACTH biosynthesis. The releasing mechanism, on the other hand, did not appear to be related to de novo synthesis. Prolonged in vivo administration of high concentrations of Dx initially caused a decrease of ACTH synthesis and, later, also impaired the synthesis of total proteins. Synthesis and release of ACTH may be dissociated, but there is a possibility that a correlation exists between these two processes. On the other hand and as far as the direct effect of Dx on the pituitary is concerned, the nuclear uptake of the steroid probably reflects an early step in the modulation of corticotropic activity.

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