Functional differentiation of the fetal anterior pituitary cells in the rat.

The onset of hormone synthesis in the rat fetal pituitary gland was studied with the use of the peroxidase labelled antibody method. On the 16th day of fetal life, cells containing immunoreactive ACTH appeared in the primordial cell outgrowth of the Rathke's pouch. In some fetuses, also prolactin cells could be detected at the same developmental stage and these cells were present consistently on subsequent days. Differentiation of ACTH and prolactin cells was followed by onset of TSH, LH and GH synthesis on the 17th, 18th and 19th day of gestation, respectively.