Endocrine Abstracts

Pomc synthesis and ACTH secretion by the anterior pituitary are controlled by two major, opposing players namely CRH and glucocorticoids. Most studies were performed on the AtT-20 mouse corticotroph tumor cell line or Pomc-transfected cells.

Aim: Aim of the present study was to evaluate the effect of CRH and DEX on Pomc expression and ACTH secretion in normal rat corticotropes in vitro.

Methods: Rat anterior pituitary primary cultures were incubated with 10 nM CRH or 10 nM DEX for 4, 24, 48, 72, 96 and 120 h prior to medium and RNA collection. Pomc gene expression was evaluated by real time PCR and ACTH was measured by IRMA.

Results: CRH stimulated ACTH secretion at 4 h and the effect was maintained for 120 h; stimulation of Pomc synthesis was evident after 24 h and increased progressively over time. DEX clearly inhibited ACTH secretion starting at 4 h, but had no effect of Pomc gene expression at any time point.

Conclusions: The present study shows that CRH stimulates ACTH synthesis and secretion by normal corticotropes while dexamethasone blunts ACTH release but appears to have no effect on Pomc synthesis. This data contrasts with results obtained in tumoral corticotropes or transfected cells and points to the need for studies on normal corticotropes in order to better understand HPA axis physiology.