Effects of diethylstilbestrol on the cytogenesis of prolactin cells in thepars distalis of the pituitary gland of the mouse

This study was carried out to examine the developmental stage when prolacti n cells differentiate in mice and to examine the effects of diethylstilbest rol on the development of prolactin cells in the fetal and neonatal pituita ry glands. A small number of immunoreactive prolactin cells appeared first on embryonic day 15 in control (injected with oil) pituitary glands, wherea s they did not increase in number until postnatal day 2. In diethylstilbest rol-treated mice (5 mg/kg body weight, 24 h before killing), a small number of immunoreactive prolactin cells were detectable as early as embryonic da y 14, but not on day 13. They increased in number on embryonic days 15 and 16, and decreased markedly on days 17 and 18, followed by a rapid increase after birth. This transient reduction in the response to diethylstilbestrol was partially restored by treatment with metyrapone, a specific inhibitor of corticosteroid production. These results suggest that in the mouse: (1) differentiation of prolactin cells occurs between embryonic days 13 and 14, (2) prolactin gene expression is suppressed in the nascent prolactin cells presumably due to the presence of high levels of estrogen-binding protein, a-fetoprotein, and (3) prolactin gene expression is also suppressed by ele vation of circulating glucocorticoids during the perinatal period. The pres ent results suggest that, in the mouse, at least a proportion of prolactin cells are not derived from growth hormone cells, because the diethylstilbes trol-induced prolactin cells appear earlier than growth hormone gene expres sion.