title: Distribution, cellular localization, and ontogeny of preprothyrotropin-releasing hormone-(160-169) (Ps4)-binding sites in the rat pituitary.
abstract: The rat TRH precursor contains five copies of TRH separated by connecting peptides. Previous studies have shown that the decapeptide prepro-TRH (160-169; Ps4) potentiates the effect of TRH on TSH secretion. In the present study, we have characterized Ps4 receptors in the rat pituitary by in vitro autoradiography using [125I-Tyr0]Ps4 as a radioligand, and we have investigated the evolution of receptor density during ontogenesis. Incubation of rat pituitary slices with [125I-Tyr0]Ps4 revealed intense binding in the anterior lobe and virtually no binding in the neurointermediate lobe. Biochemical characterization of the Ps4-binding sites suggested the existence of a single class of sites exhibiting high affinity for [Tyr0]Ps4 (IC50 = 8.3 +/- 1.2 nM) and a much lower affinity for Ps4 (IC50 = 9.3 +/- 1.2 microM). Emulsion-coated cytoautoradiography performed on cultured anterior pituitary cells showed that only 26% of the cells possessed [125I-Tyr0]Ps4-binding sites. Immunocytochemical analysis using antibodies against the different anterior pituitary hormones indicated that the cells possessing [125I-Tyr0]Ps4-binding sites did not correspond to TSH-, PRL-, GH-, ACTH-, or LH-secreting cells. In contrast, cells expressing Ps4 receptors were immunoreactive for the S-100 protein, a marker of folliculo-stellate cells. During postnatal development, a 4-fold increase in the concentration of [125I-Tyr0]Ps4-binding sites occurred from birth to weaning in the pituitary, with a marked and transient increase at the time of weaning. Thereafter, the density of sites declined gradually until day 60. In conclusion, the present study shows that folliculo-stellate cells express [125I-Tyr0]Ps4-binding sites in the anterior pituitary, and that these sites are developmentally regulated. The present data suggest that the potentiating effect of Ps4 on TRH-induced TSH secretion is mediated by folliculo-stellate cells.
authors.affiliation: European Institute for Peptide Research (IFRMP 23), Institut National de la Santé et de la Recherche Médicale U-413, Unité Affilieé au Centre National de la Recherche Scientifique, University of Rouen, Mont-Saint-Aignan, France.
authors.forename: K
authors.initials: K
authors.lastname: Valentijn
authors.forename: F
authors.initials: F
authors.lastname: Vandenbulcke
authors.forename: E
authors.initials: E
authors.lastname: Piek
authors.forename: J C
authors.initials: JC
authors.lastname: Beauvillain
authors.forename: H
authors.initials: H
authors.lastname: Vaudry
mesh_terms: D000367:Age Factors; D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D007150:Immunohistochemistry; D007457:Iodine Radioisotopes; D008297:Male; D010446:Peptide Fragments / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*
chemical_list: D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D011498:Protein Precursors; C057639:prepro-thyrotropin releasing hormone (160-169); D013973:Thyrotropin-Releasing Hormone