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Cellular Localization of Orexin Receptors in Human Pituitary*

Departments of Morphological Sciences (M.B., T.G.-C., R.G., A.V.-B., A.B.), Physiology (M.L., R.S., C.D.), and Medicine (F.C.), School of Medicine–University Clinical Hospital, University of Santiago de Compostela, E-15782 Santiago de Compostela, Spain; and Centre National de la Recherche Scientifique UMR 5578 (G.M.), Université Claude Bernard-Lyon 1, Villeurbane, France

Address correspondence and requests for reprints to: Prof. Tomás García-Caballero, Department of Morphological Sciences, School of Medicine, University of Santiago de Compostela, San Francisco, E-15782 Santiago de Compostela, Spain. E-mail: cmhisihq{at}usc.es

Orexins-A and -B are hypothalamic peptides derived from a precursor called prepro-orexin and relationated with the stimulation of food intake. They act on G protein receptors named orexin receptor 1 (OX₁R) and orexin receptor 2 (OX₂R), respectively. In the present study, we used RT-PCR and immunohistochemical techniques to detect the presence of OX₁R and OX₂R in human pituitary. A band of the expected size for both OX₁R and OX₂R was shown in human pituitary by RT-PCR. The cellular localization of OX₁R and OX₂R was carried out using histological techniques. By consecutive sections we demonstrated that OX₁R was present in acidophil, diffusely distributed cells, which represent the half of the total adenohypophysis cell population. As was expected, these cells were shown to coexpress GH. OX₂R was found in the pars intermedia and in clusters of basophil cells of the anterior pituitary, which coexpress ACTH. These results were confirmed by double immunofluorescence techniques. We also found focal positivity in axon terminals of neurohypophysis, more intense for OX₂R than for OX₁R. In conclusion, these results demonstrated for the first time that OX₁R and OX₂R were expressed by somatotrope and corticotrope cells, respectively.

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