Expression of guanylin in “pars tuberalis-specific cells” and gonadotrophs of rat adenohypophysis

Abstract

The intestinal peptide guanylin regulates the electrolyte͞water transport in the gastrointestinal epithelium by paracrine͞lumino-crine mechanisms. Because guanylin also circulates in the blood, we investigated the rat hypothalamo-pituitary region for expression and cellular localization of this peptide. Reverse transcriptase-PCR analyses with guanylin-specific primers revealed expression of the peptide in the pars tuberalis and pars distalis of the pituitary. Western blotting analyses in hypophyseal tissue extracts identified the expected 12.5-kDa immunoreactive peptide by using two different region-specific guanylin antisera. Light and electron microscopic immunocytochemistry with the same antisera localized guanylin in ''pars tuberalis-specific cells'' in the juxtaneural pars tuberalis adjacent to nerve endings and blood vessels of the hypothalamo-pituitary portal system and in gonadotrophic cells within the distal pars tuberalis and ventrolateral part of the pars distalis. The presence and cell-specific localization of guanylin within the hypothalamo-hypophyseal system indicate that this peptide may be specifically involved in paracrine and endocrine regulatory mechanisms.guanylate cyclase C-activating peptides ͉ pituitary gland ͉ regulatory peptides ͉ gonadotrophic cells

Photoperiodic regulation of prolactin secretion: changes in intra-pituitary signalling and lactotroph heterogeneity

“…The extensive list of secretory molecules expressed in PT-specific cells (reviewed in Wittkowski et al 1999) has recently been extended (D'Este et al 2000, Guerra & Rodriguez 2001. However, the ability of many of these molecules to fulfil the putative physiological role of tuberalin has not been rigorously examined.…”

Guanylin-immunoreactive cells in the female and male rat adenohypophysis and their changes under various physiological and experimental conditions

“…After localization of guanylin to pars tuberalis of male rat adenohypophysis (D'Este et al 2000), we extended our investigations to the adenohypophysial pars distalis of female rats and studied the respective GUAN-IR cells under various physiological conditions and after gonadectomy of rats of both sexes. These studies were aimed to identify the cells containing guanylin in the hypophysis and their sensitivity and correlative changes to sex hormonal regulation in the hypophysis-gonad axis.…”

“…Indeed, guanylin was localized to endocrine cells in the intestine, i.e., enterochromaffin cells (Cetin et al 1994), and to endocrine organs including the adrenal and pituitary glands (Reinecke et al 1996;D'Este et al 2000). It has been assumed that this peptide exerts functions other than transepithelial transport of electrolytes and water in surface epithelia (D'Este et al 2000).…”

“…We used two region-specific rabbit antisera directed against proguanylin-82-93 [antiserum EG(2)Gua] and proguanylin-101-115, guanylin itself (antiserum K605). Both antisera have been characterized and used in previous studies (Cetin et al 1994(Cetin et al , 1995D'Este et al 2000;Cetin 2001, 2002;Kulaksiz et al 2001aKulaksiz et al , b, 2002aVaccaro et al 2004). The antisera were diluted at 1:25,000-1:50,000 in PBST/ BSA, and PBST was used for the washing steps.…”

“…Accordingly, guanylin was localized within the adrenal gland (Reinecke et al 1996), and more recently our group localized it in the rat pituitary pars tuberalis, within the specific cells of the ''pars tuberalis'' and a subpopulation of resident gonadotrophic cells (D'Este et al 2000) which at least argues for a role of guanylin in the reproduction physiology. This is further substantiated by studies demonstrating the presence of guanylin or of its receptor in reproductive tissues (Forte et al 1989;Krause et al 1990;Schulz et al 1992;Fan et al 1997;Jaleel et al 2002).…”