INDUCTION OF CLASSICAL LACTOTROPES BY EPIDERMAL GROWTH-FACTOR IN RAT PITUITARY CELL-CULTURES

Long term incubation of pituitary tumor GH(3) cultures with epidermal growth factor (EGF) induces reciprocal changes in PRL and GH productio n. However, it is not known whether EGF alters the cellular compositio n of these cultures. Another unanswered question is whether chronic tr eatment with EGF stimulates PRL secretion from nonneoplastic pituitary cells. In this study, GH(3) cells and pituitary cells from neonatal ( 10-day-old) rats were cultured for 6 and 2 days, respectively, in the absence or presence of 5 nM EGF. Cells containing PRL and/or GH were t hen enumerated using light microscopic immunocytochemistry. In additio n, neonatal pituitary cells were subjected to reverse hemolytic plaque assays for PRL. EGF treatment drastically increased the proportion of classical lactotropes (cells that secrete only PRL) in the GH(3) cult ures, from about 0.5% to 8% of all cells, without modifying the percen tage of GH-positive cells. A similar action of EGF was observed in the primary cultures. Moreover, EGF enhanced by 240% the amount of PRL se creted from the neonatal lactotrope population during 1-h incubations under basal conditions. This effect was mediated by a selective increa se in the relative number of PRL secretors forming large plaques. The results suggest that EGF promotes the differentiation of classical lac totropes in both GH(3) cultures and pituitary cultures from neonatal r ats, and that these cells are characterized by a high basal rate of PR L secretion.