PRL and pituitary gland adenoma: The PIT1 protein, which is a transcription factor whose presence is required in utero for normal development of the mammosomatropes that produce GH and PRL, is also required for the maintenance of normal expression of GH, prolactin, and TSH after the separate embryonic origin of thryotropes and has been postulated to play a role in the development of co-secretory pituitary adenomas (13).