MITOGENIC EFFECTS OF NERVE GROWTH-FACTOR ON DIFFERENT CELL-TYPES IN REAGGREGATE CELL-CULTURES OF IMMATURE RAT PITUITARY

Treatment of reaggregate pituitary cell cultures of 14-day-old female rats with nerve growth factor (NGF) augmented the number of [H-3]thymi dine ([H-3]T)-incorporating lactotrophs in a dose-dependent manner (0. 03-3 nM). At least during short-term treatment NGF increased the total number of cells expressing prolactin (PRL) mRNA and enlarged the cyto plasmic area occupied by PRL mRNA but did not affect the number of cel ls and the cytoplasmic area containing PRL, suggesting that NGF recrui ts lactotrophs expressing PRL mRNA. but not yet PRL. NGF also stimulat ed [H-3]T incorporation in ACTH cells but not in somatotrophs, thyrotr ophs and gonadotrophs. In addition, NGF augmented the total number of [H-3]T-incorporating cells to a much higher extent than was expected f rom its effect on lactotrophs and ACTH cells, suggesting NGF also stim ulates [H-3]T-incorporation in non-hormone producing cells (progenitor s or stem cells?). Around 40% of these [H-3]T-incorporating cells in b oth control and NGF treated cultures showed immunoreactivity for the t ranscription factor Pit-1 in the nuclei, which is twice the percentage expected (18%) if these [H-3]T-incorporating cells were the only know n Pit-1 expressing cells in the pituitary i.e. lactotrophs, somatotrop hs and thyrotrophs. The present data suggest that NGF has a mitogenic effect on several cell lineages in the pituitary: lactotrophs, cortico trophs and non-hormone-containing cells. The high proportion of mitoti c non-hormone containing cells that express Pit-1 is consistent with t he proposed role of Pit-1 in cell proliferation in the developing lact osomatotroph lineage. (C) 1997 Elsevier Science Ireland Ltd.