Different behavior of lactotroph cell subpopulations in response to angiotensin II and thyrotrophin-releasing hormone.

1. In the present investigation we have extended the study of lactotroph subpopulations in primary pituitary cell cultures. Male rats with or without previous estrogenization followed by A-II or TRH treatments were selected as experimental models. 2. The TRH increased up to 50% the PRL released in both whole and OROX+EB rats (P < 0.05). In contrast, A-II treatment introduced no changes in PRL secretion from cell cultures derived from whole male rats but attained a significant augmentation (about 75%) of PRL secreted by ORQX+EB pituitary cells. 3. The addition of TRH and A-II to cultures of ORQX+EB-derived lactotrophs induced cytological changes compatible with a high secretory activity. In estrogen-treated rats the prevailing lactotroph subpopulation is type I. In cell cultures from control and A-II treated whole male pituitaries, the majority of lactotrophs consists of atypical subpopulations of II and III cells, with smaller secretory granules (between 150 and 300 nm in diameter). 4. Morphometry of immunostained lactotrophs performed on light microscopic preparations revealed that about 30-36% of the total cell count were lactotrophs. This percentage was fixed and did not change significantly after TRH and A-II treatments. 5. The present results confirm the presence of morphological and functional subtypes of lactotroph cells in rat pituitary. Typical PRL cell population shows the highest responsiveness to angiotensin II and TRH action. This functional heterogeneity of lactotroph subtypes may reflect an important and scarcely explored factor in the regulatory process of prolactin secretion.