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.