Changes of Cell Morphology and Prolactin Secretion Induced by 2-Br-«-Ergocryptine, Estradiol, and Thyrotropin-releasing Hormone in Rat Anterior Pituitary Cells in Culture

The secretion of prolactin in cultured pituitary cells was studied in correlation with the cellular changes induced by stimulatory or inhibitory agents . The techniques used in this study were : radioimmunoassay, immunocytochemistry, scanning (SEM) as well as transmission (TEM) electron microscopy . Prolactin secretion was stimulated by 17,8-estradiol (10 nM) as well as thyrotropin-releasing hormone (TRH) (3 nM) and inhibted by 2-Br-a-ergocryptine (CB-154) (1 ftM) . The total prolactin (release and cell content) increased between 2 and 8 d of estradiol treatment, indicating an increase of both synthesis and release of prolactin . This finding was in agreement with TEM observations because, in estradiol-treated prolactin cells, the Golgi saccules were distended and Golgi elements were increased, thus indicating increased synthetic activity of these cells. The addition of TRH over a 4-h period resulted in a significant degranulation of prolactin cells. In contrast, prolactin secretory granules became accumulated in the cells after CB-154 treatment for a period ranging from 4 to 24 h. In agreement, light microscope immunocytochemistry showed an increased reaction for prolactin after short-term (<24 h) incubation with CB-154 . Because prolactin cells represent --70% of the glandular cell population as revealed by immunocytochemistry, it was then possible to observe the changes of cell surface by SEM. In most cells, estradiol and TRH led to an increase in the number and prominence of microvilli and blebs, whereas CB-154 treatment resulted in a slightly decreased number of microvilli and an increased occurrence of membrane foldings . This report thus provides morphological evidence for the stimulatory effects of estradiol and TRH, and the inhibitory effects of CB-154 on prolactin secretion in pituitary cells in primary culture. These data, moreover, show that acute changes in secretory activity of prolactin-secreting cells are accompanied by marked changes of their morphological characteristics . The secretion of prolactin in the anterior pituitary gland is under predominant inhibitory control by the hypothalamus (30) . Recent data indicate that dopamine may be the main or even the only inhibitory substance of hypothalamic origin involved in the control of prolactin secretion (11, 29, 37) . This role ofdopamine is also supported by the finding that 2-bromoa-ergocryptine (CB-154), a potent dopamine agonist, and other THE JOURNAL of CELL i31OLOGV " VOLUME 86 AueusT 1980 377-387 © The Rockefeller University Press " 0021-9525/80/08/0377/11 $1 .00 ergot derivatives are potent inhibitors of prolactin secretion in vivo as well as in vitro (16, 26, 31, 33) . The stimulatory influence of the hypothalamus can, at least partly, be mediated by thyrotropin-releasing hormone (TRH) . This tripeptide is known to stimulate prolactin secretion in vivo (7, 14) and in vitro (15, 38) . Prolactin secretion is also well known to be increased after estrogen treatment in man (10, 39) 377 on A uust 8, 2017 jcb.rress.org D ow nladed fom and the rat (13) . Recently, estrogens have been found not only to stimulate prolactin secretion but also to reverse the inhibitory effects of dopamine agonists (including CB-154) by a direct action at the pituitary level (26, 34) . Pituitary cells in primary culture (25, 38) offer an attractive system for the study of cells by scanning electron microscopy and permit a precise correlation with changes of pituitary hormone secretion induced by various stimulatory or inhibitory agents. In preliminary reports (1, 2), we have recently described a good correlation between the surface morphology of anterior pituitary cells in primary culture and prolactin and thyroidstimulating hormone (TSH) secretion after shortand longterm treatment with estrogens, CB-154, triiodothyronine, TRH, and colchicine (3) . In the present report, we have used immunocytochemical localization of prolactin, scanning and transmission electron microscopy, and radioimmunoassay data for each experimental condition, to describe the effects and interactions of l7ß-estradiol (E2), TRH, and CB-154 in this system at the cellular level. MATERIALS AND METHODS