Negative regulation by dexamethasone of the potentiation of neuromedin C-induced growth hormone and prolactin release by estradiol in anterior pituitary cell aggregates.

The bombesin-like peptide neuromedin C (NMC) stimulated the release of growth hormone (GH) and prolactin (PRL) from adult male rat anterior pituitary cell aggregates cultured in serum-free medium. This effect, particularly on GH release, was significantly increased when the cells were cultured in the presence of estradiol (E2). The GH response to NMC was not affected by 4 nM dexamethasone (Dex) but was enhanced in the presence of 80 nM Dex. However, the strong stimulatory action of E2 on the GH response to NMC was completely abolished by 4 nM Dex. In contrast, the PRL response to NMC was reduced by 4 nM Dex and this to a proportionally similar extent in the presence or absence of E2. The present data show that glucocorticoids can be both positive and negative regulators of the same response system.