Local action of estrogen and thyroid hormone on vasoactive intestinal peptide (VIP) and galanin gene expression in the ratanterior pituitary

Abstract

Neuropeptides act within the pituitary as autocrine or paracrine factors, modulating the synthesis and release of primary pituitary hormones, and possibly regulating cell proliferation and/or plasticity. Manipulation of the endocrine status of rats produces dramatic long-term changes in the pituitary expression of several peptides, including the neuropeptides galanin and vasoactive intestinal peptide (VIP). Whether or not these changes are caused indirectly by hypothalamic factors, or by hormone actions directly in the pituitary, has been only partially addressed. To determine if estrogen or thyroid hormone can act directly within the pituitary to regulate VIP and galanin gene expression, cultured female rat pituitary cells were treated with 10nM 1,17 β-estradiol (E2) or triiodothyronine (T3). E2treatment for three days resulted in an approximate 5-fold and 7-fold increase in VIP and galanin mRNA, respectively. In contrast, T3 treatment reduced the mRNA levels of these neuropeptides to approximately 40% and 30% of control values. A time course study indicated that the actions of estrogen on VIP and galanin mRNA, and of thyroid hormone on VIP mRNA were readily apparent after 24h.The rat pituitary tumor cell line RC-4B/C was found to express easily detectable levels of galanin but not VIP mRNA. Galanin gene expression in these cells was moderately increased by E2 and decreased by T3. Transfection of a series of luciferase plasmids containing 5kb to 131bp of the bovine galanin promoter fused to luciferase revealed cell-type specific enhancer sequences located between −452 and −131bp of the galanin gene transcription start site. However, transfected plasmids were minimally responsive to E2 and T3 treatment. Overall the results suggest that E2 and T3 exert significant local actions in the pituitary on VIP and galanin gene expression. The bovine galanin gene fragment used in these studies contains a potential pituitary cell-type specific enhancer, but appears to lack strong E2-and T3-responsive sequences.