Expression of guanylin in "pars tuberalis-specific cells" and gonadotrophsof rat adenohypophysis

The intestinal peptide guanylin regulates the electrolyte/water transport i n the gastrointestinal epithelium by paracrine/luminocrine mechanisms. Beca use guanylin also circulates in the blood, we investigated the rat hypothal amo-pituitary region for expression and cellular localization of this pepti de. Reverse transcriptase-PCR analyses with guanylin-specific: primers reve aled expression of the peptide in the pars tuberalis and pars distalis of t he pituitary. Western blotting analyses in hypophyseal tissue extracts iden tified the expected 12.5-kDa immunoreactive peptide by using two different region-specific guanylin antisera, Light and electron microscopic immunocyt ochemistry with the same antisera localized guanylin in "pars tuberalis-spe cific cells" in the juxtaneural pars tuberalis adjacent to nerve endings an d blood vessels of the hypothalamo-pituitary portal system and in gonadotro phic cells within the distal pars tuberalis and ventrolateral part of the p ars distalis, The presence and cell-specific localization of guanylin withi n the hypothalamo-hypophyseal system indicate that this peptide may be spec ifically involved in paracrine and endocrine regulatory mechanisms.