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 ac t on G protein receptors named orexin receptor 1 (OX1R) and orexin receptor 2 (OX2R), respectively. In the present study, we used RT-PCR and immunohis tochemical techniques to detect the presence of OX1R and OX2R in human pitu itary. A band of the expected size for both OX1R and OX2R was shown in huma n pituitary by RT-PCR. The cellular localization of OX1R and OX2R was carri ed out using histological techniques. By consecutive sections we demonstrat ed that OX1R was present in acidophil, diffusely distributed cells, which r epresent the half of the total adenohypophysis cell population. As was expe cted, these cells were shown to coexpress GH. OX2R was found in the pars in termedia 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 neurohypoph ysis, more intense for OX1R than for OX2R. In conclusion, these results dem onstrated for the first time that OX1R and OX2R were expressed by somatotro pe and corticotrope cells, respectively.