Immunofluorescence evidence of melanotrophs in the pituitary of four odontocete species. An immunohistochemical study and a critical review of the literature.

Cetaceans share peculiar features of their pituitary glands, with a complete separation of pars distalis and pars nervosa by a dural septum and the absence of an intermediate lobe and cleft. In most mammals the pars intermedia is the main source of circulating alpha-melanocyte stimulating hormone (alpha-MSH), derived from a large precursor called proopiomelanocortin (POMC), which also generates adrenocorticotropic hormone (ACTH) in the adenohypophysis. The lack of an intermediate lobe in cetaceans led us to investigate whether their glands are able to produce alpha-MSH, and if this hormone is secreted by a distinct population of melanotrophs or by corticotrophs in the pars distalis. Irnmunofluorescence evidences seem to support the first assumption, with ACTH-immunoreactive (-ir) elements rarely overlapping with alpha-MSH-ir ones. The discovery of a population of true melanotrophs in the hypophysis of some odontocetes underscores the need for further research on the melanocortin system of cetaceans (C) 2013 Elsevier GmbH. All rights reserved.