Epidermal growth factor enhances ACTH secretion and expression of POMC mRNA by corticotropes in mixed and enriched cultures

Previous studies have shown that epidermal growth factor (EGF) stimulates the release of adrenocorticotropin (ACTH) in vivo and in vitro by amplifying the effects of corticotropen-releasing hormone (CRH). The aim of the present studies was to compare responses to EGF by corticotropes in an unseparated culture with those in cultures enriched to 90-93% ACTH-β-endorphin cells (by counterflow centrifugation). Since EGF binding sites had been identified on growth hormone (GH) or prolactin (PRL) cells (9), the enriched corticotrope cultures were studied to learn if the abundant GH or PRL cells found in unseparated cultures were required to mediate the actions of EGF. In unseparated cultures, EGF (1 or 10 ng/ml) or CRH (1-5 nM) increased the percentages of ACTH cells from 9.5 to 15% and the percentage of cells labeled for POMC mRNA from 7.5 to 12% of the population. In enriched cultures, CRH and EGF increased the percentages of cells labeled for POMC mRNA from 70% to 90-94% of the population. EGF alone stimulated ACTH secretion in both the unseparated and enriched cultures by 1.2- to 2.2-fold. EGF amplified the effects of CRH by 30-40% in both unseparated and enriched cultures. In unseparated cultures grown in serum-free media, however, 1 ng/ml EGF did not amplify the effects of CRH and 10 ng/ml EGF partly abolished the CRH stimulation. In contrast, enriched cultures grown in serum-free media continued to respond to the growth factor. the secretory responses of corticotropes in enriched cultures were similar to those of their counterparts in the unseparated cultures. This indicates that the reduction in numbers of GH and PRL cells in the enriched cultures does not interfere with EGF actions on the corticotrope population.