NERVE GROWTH-FACTOR PROMOTES THE DIFFERENTIATION OF PITUITARY MAMMOTROPH CELLS IN-VITRO

It is well known that the differentiation of somatotroph cells is depe ndent on GRF. The extracellular signals that direct the initial prolif eration and differentiation of mammotroph cells during pituitary devel opment, however, have remained elusive. In the present study we first report that somatomammotroph and mammotroph cells present in early pos tnatal rat pituitary cultures express the receptor for nerve growth fa ctor (NGF) and contain NGF. In addition, we demonstrate that endogenou s NGF supports the proliferation and terminal differentiation of mammo troph cells during postnatal in vitro maturation. Early postnatal rat pituitary cells were cultured for 1-12 days, double stained with antib odies to PRL and GH, and analyzed by fluorescence-activated cell sorti ng. Mature mammotroph cells were generated in culture as shown by 1) t he increase in PRL production, 2) the spreading of cells secreting onl y PRL in relation to those producing both PRL and GH, and 3) the expre ssion of D-2 receptors for dopamine. Exposure of cell cultures to NGF produced a remarkable increase in the rate of appearance of mammotroph cells and an increase in their abundance from 20 +/- 0.5% to 44 +/- 1 %. Deprivation of secreted NGF by means of a specific antibody complet ely prevented the generation of mature mammotrophs. The fluorescence-a ctivated cell sorting analysis of cells grown in the presence of the a ntibody to NGF showed, in fact, that although the proportions of somat otrophs and somatomammotrophs were unchanged, that of mammotrophs was much lower than that in untreated cultures. We, thus, conclude that NG F is critical for generation of the mammotroph phenotype during pituit ary maturation.