Orexin-A (hypocretin 1)-like immunoreactivity in growth hormone-containing cells of the Japanese seaperch (Lateolabrax japonicus) pituitary

Immunohistochemical techniques were employed to investigate the distribution of orexin-A-like immunoreactivity in the Japanese seaperch (Lateolabrax japonicus) pituitary. Orexin-A-immunoreactive cells were concentrated in the proximal part of the pars distalis. We found that these cells corresponded to the cells immunostained with antiserum against salmon growth hormone (sGH). Immunoelectron microscopic analysis indicated that the orexin-A-like substance and GH coexisted in the secretory granules. Western blot analysis of seaperch pituitary extract revealed that anti-human orexin-A serum labeled approximately 16.2- and 8.0-kDa bands, which were not labeled with anti-sGH serum. The orexin-A-like substance in the pars distalis may participate in the modulation of pituitary functions together with GH in the seaperch.