The effects of estrogen on prolactin cells of the male rat pituitary. An immunocytologic and autoradiographic study.

Both immunoperoxidase staining (to identify specifically prolactin cells) and autoradiography after labelling with 3H-thylmidine (to demonstrate those cells which actively produce DNA) were performed on the same sections from normal male rat pituitaries and on those from rats treated with 17 beta-estradiol. In normal pituitaries, 3.3% of prolactin cells appeared to take up 3H-thymidine. Estrogen stimulation produced an increase in the weight of the pituitary and in the percentage of immunostained as well as of labelled prolactin cells, indicating that proliferation of prolactin cells at least in part accounted for the enlargement of the pituitary. The question, whether prolactin cell hyperplasia was due to multiplication of pre-existing, well differentiated prolactin cells or of immature prolactin cell precursors, remains to be elucidated.