Since the downregulation of the cAMP-PKA-CREB pathway constitutes a mechanism of DA treatment for pituitary adenomas [18], we confirmed that DA can downregulate p300 expression by inhibiting the cAMP-PKA-CREB pathway in cultured MMQ and AtT-20 cells, indicating that p300 downregulation is related to DA-mediated resistance. Here, CREB1 is linked to pituitary gland adenoma.