MTTW-10 PITUITARY-TUMOR CELLS - GALANIN GENE-EXPRESSION AND PEPTIDE SECRETION

The peptide galanin is synthesized within and secreted from specific c ell types of the rat anterior pituitary gland. The small size of the r at anterior pituitary gland is somewhat limiting for studying the regu lation of galanin gene expression and peptide synthesis/secretion. We examined the mammotropic rat pituitary tumor MtTW-10 as a possible mod el system to study galanin. The objectives of this study were to 1) de termine if galanin is secreted from MtTW-10 cells in vitro in a regula ted manner, 2) characterize the molecular forms of immunoreactive gala nin secreted by MtTW-10 cells, and 3) assess whether galanin gene expr ession in MtTW-10 tumors is regulated by estradiol. MtTW-10 pituitary tumors were transplanted to female Wistar-Furth rats that were implant ed with estradiol-filled capsules. Cells were harvested from the MtTW- 10 tumors and cultured for 4 days. When examined by electron microscop y, the MtTW-10 cells maintained in culture were irregular in shape wit h microvilli on their surface and contained numerous large secretory g ranules. Immunoreactive galanin, PRL, and GH were secreted from the ce lls in a time-dependent fashion during static incubations. LH, ACTH, a nd TSH were undetectable in the culture medium. Somatostatin (10 and 1 00 nm) inhibited galanin, PRL, and GH release in a dose-dependent mann er. In contrast, dopamine, TRH, LH-releasing hormone, CRH, and GH-rele asing hormone at concentrations of 10-100 nm failed to alter hormone s ecretion. Only high concentrations of dopamine (1 muM) inhibited the s ecretion of galanin, PRL, and GH. HPLC fractionation of peptides secre ted by MtTW-10 cell cultures showed that approximately 84% of the gala nin immunoreactivity coeluted with synthetic rat galanin. In tumor-bea ring rats, plasma levels of immunoreactive galanin were 10-fold higher after estradiol treatment than levels in ovariectomized controls. Gal anin mRNA levels were increased 20-fold by estradiol in MtTW-10 tumors , as determined by solution hybridization, and peptide levels were ele vated nearly 100-fold. We conclude that 1) galanin is secreted from Mt TW-10 cells in vitro, and its secretion is inhibited by somatostatin; and 2) estradiol increases galanin gene expression and peptide secreti on in MtTW-10 tumors in vivo. These data show that MtTW-10 tumors may be useful to study the regulation of pituitary galanin gene expression , peptide synthesis, and secretion.