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Distribution, Cellular Localization, and Ontogeny of Preprothyrotropin-Releasing Hormone-(160–169) (Ps4)-Binding Sites in the Rat Pituitary¹

European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, Institut National de la Santé et de la Recherche Médicale (INSERM U-413), Unité Affilieé au Centre National de la Recherche Scientifique (UA CNRS), University of Rouen (K.V., E.P., H.V.), 76821 Mont-Saint-Aignan; and the Laboratory of Neuroendocrinology and Neuronal Pathology, INSERM U-422 (F.V., J.C.B.), 59045 Lille, France

Address all correspondence and requests for reprints to: Dr. H. Vaudry, European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, Institut National de la Santé et de la Recherche Médicale (INSERM U-413), Unité Affiliée au Centre National de la Recherche Scientifique (UA CNRS), University of Rouen, 76821 Mont-Saint-Aignan, France. E-mail: hubert.vaudry{at}univ-rouen.fr

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 µM). 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.

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