Cellular localization of orexin receptors in human pituitary

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 OX1R than for OX2R. In conclusion, these results demonstrated for the first time that OX1R and OX2R were expressed by somatotrope and corticotrope cells, respectively.