Function of Galanin in the Anterior Pituitary of Estrogen-Treated Fischer 344 Rats: Autocrine and Paracrine Regulation of Prolactin Secretion

Abstract

Estrogen is a robust stimulator of galanin synthesis and secretion in the anterior pituitary. Galanin is colocalized in lactotrophs in the estrogen-treated anterior pituitary, and its roles in lactotroph function are still being elucidated. In the present studies, we quantified the phenotypes of estrogen-treated Fischer 344 rat anterior pituitary cells expressing the galanin gene by dual in situ hybridization. The total population of galanin-positive pituitary cells increased from undetectable levels to 16% of all cells after 2 weeks of estrogen treatment. More than 90% of the galanin-positive cells coexpressed PRL messenger RNA, and one-third of the lactotrophs expressed galanin messenger RNA. We hypothesized that galanin in the anterior pituitary may contribute to the heterogeneous secretion of PRL, and that one of the functions of galanin is to regulate PRL secretion in an autocrine/paracrine manner. To test this hypothesis, we performed the reverse hemolytic plaque assay combined with in situ hybridization to measure PRL secretion and galanin gene expression within the same individual cells. PRL secretion from galanin-positive lactotrophs was significantly greater than that from galanin-negative lactotrophs. Moreover, treatment with galanin antiserum significantly attenuated PRL secretion from galanin-positive cells, and treatment with galanin significantly enhanced PRL secretion from galanin-negative lactotrophs. In conclusion, these data provide direct evidence that galanin derived from the estrogen-treated anterior pituitary stimulates PRL secretion in both autocrine and paracrine manners.

Calcitonin is expressed in gonadotropes of the anterior pituitary gland: its possible role in paracrine regulation of lactotrope function

“…It has been suggested that several effects of estrogens on lactotrope function and proliferation are mediated by lactotrope-derived VIP and galanin (Wynik et al 1993, Cai et al 1998. Similarly, our studies suggest that CT inhibits PRL release and PRL gene transcription, and also attenuates thyrotropin-releasing hormone (TRH)-and suckling-induced PRL release and synthesis (Shah et al 1988, Judd et al 1990.…”

Topographic Affinities of Hormone-Producing Cells in the Rat Anterior Pituitary Gland.

“…1, 10, 13) is consistent with the idea of cell-tocell interactions by means of gap junctions. Many kinds of bioactive proteins other than the classic types of hormones have been found in the pituitary gland with immunohistochemical methods; e.g., angiotensin II [5,13], PACAP [8] and galanin [4,12]. These peptides are attractive candidates for paracrine factors regulating hormone secretion.…”

Implication of Pituitary Vasoactive Intestinal Peptide in Dopaminergic Inhibition of Estrogen-Induced Pituitary Hyperplasia and Vascular Endothelial Growth Factor Expression

“…As Fischer 344 (F344) rats are particularly sensitive to this action, this strain has been commonly used to study the mitogenic action of E at the pituitary. Different endocrine and autocrine/paracrine factors, such as disruption of the dopaminergic axis [4, 5], transforming growth factor (TGF) beta 1 [6], TGF-β3 [7], basic fibroblast growth factor [8], or galanin [9, 10], are known to be involved in the mediation of the E-proliferative effect on lactotropes. However, it is still not well understood how these mechanisms are coordinated to induce lactotrope hyperplasia and tumorigenesis.…”