Galanin and vasoactive intestinal polypeptide are colocalised with classical pituitary hormones and show plasticity of expression

Abstract

The identity of galanin- and vasoactive intestinal polypeptide-(VIP) immunoreactive (IR) cells in the rat anterior pituitary was investigated using immunocytochemistry and, since levels of both peptides are stimulated by oestrogen, the effect of oestrogen treatment and gonadectomy on the expression of both peptides was examined. In normal male rats, few galanin-IR and very few VIP-IR cells were found. Colocalisation studies performed on 2-microns serial paraffin sections revealed that in these animals galanin IR was present in somatotrophs and thyrotrophs. In normal females in dioestrus many lactotrophs, in addition to somatotrophs and thyrotrophs, expressed galanin, but very few VIP-IR cells were seen. In cryostat sections of normal rat pituitaries, slightly more VIP-IR cells were present. Oestrogen treatment in females produced an increase in frequency of galanin-IR cells, the vast majority of which were lactotrophs, and more VIP-IR cells, identified as lactotrophs, also appeared. VIP was present in a subset of galanin-IR lactotrophs after oestrogen treatment. After ovariectomy female pituitaries resembled those of normal males, with few galanin positive cells none of which were lactotrophs, and hardly any VIP-IR cells. Thus these two peptides are present in specific endocrine cell types of rat anterior pituitary and display plasticity of expression in different cell types under the influence of oestrogen. Their roles in control of pituitary hormone secretion are supported by these findings, and it is possible that both peptides act in a paracrine fashion within the pituitary.

Cellular localization of apelin and its receptor in the anterior pituitary: evidence for a direct stimulatory action of apelin on ACTH release

“…Apelin is not the only "hypothalamic" peptide that colocalizes with both hormones. Three other peptides have also been detected within ACTH-and GH-containing cells, such as galanin (6,37), neuromedin U (6), and leptin (41). Interestingly, these peptides are involved in the regulation of food intake (13,17,28), and adipocyte apelin mRNA expression was recently reported to be increased in various mouse models of obesity associated with hyperinsulinemia (2).…”

Identification of Galanin-Immunoreactive Cells in the Anterior Pituitary of Male Monkeys (Macaca fascicularis).

“…The differences among the monkey, human and rat in GAL-immunoreactive localization may indicate that the regulation of GAL in the three species differs. Recently, GAL-LI was observed in the anterior lobe of the pituitary of rats and humans by means of immunohistochemistry [14][15][16][17]. Moreover, GAL mRNA within the anterior lobe of rats has been demonstrated by in situ hybridization [15,16,18].…”

Transgenic mice over-expressing galanin exhibit pituitary adenomas and increased secretion of galanin, prolactin and growth hormone

“…In Dwarf mice, where there is failure of acidophilic proliferation, galanin is also lacking (Hyde et al 1993). We and others have previously demonstrated that galanin is dramatically up-regulated by oestrogens in the anterior pituitary (Kaplan et al 1988, Vrontakis et al 1989, primarily within the lactotrophs of both sexes (Steel et al 1989, Hyde et al 1991, suggesting that the peptide can be present in the same cell type in males and females, depending on the status of oestrogen levels. During pituitary hyperplasia, induced by oestrogen, a correlation exists between the development of pituitary hyperplasia and the increase in galanin mRNA (messenger ribonucleic acid) and peptide concentration (Vrontakis et al 1987, Kaplan et al 1988, Hsu et al 1990.…”

“…Immunohistochemical studies indicate that in normal female rats, galanin is detected mainly in lactotrophs, and to a lesser extent in somatotrophs and thyrotrophs (Steel et al 1989, Hyde et al 1991. In the male rat, on the other hand, galanin expression has been confirmed in somatotrophs and, in some studies, thyrotrophs (Steel et al 1989, Moore et al 1999. In Dwarf mice, where there is failure of acidophilic proliferation, galanin is also lacking (Hyde et al 1993).…”

“…In humans, intravenous administration of galanin increases plasma GH levels (Bauer et al 1986) and enhances the GH response to exogenous growth hormone releasing hormone (GHRH) (Davis et al 1987, Carey et al 1993, Chan et al 1996. Immunohistochemical studies indicate that in normal female rats, galanin is detected mainly in lactotrophs, and to a lesser extent in somatotrophs and thyrotrophs (Steel et al 1989, Hyde et al 1991. In the male rat, on the other hand, galanin expression has been confirmed in somatotrophs and, in some studies, thyrotrophs (Steel et al 1989, Moore et al 1999.…”