Identification of an urotensin I-like peptide in the pituitary of the lungfish Protopterus annectens: immunocytochemical localization and biochemicalcharacterization

In the present study we have investigated the localization and biochemical characteristics of urotensin I (UI)-like and urotensin II (UII)-like immuno reactive peptides in the central nervous system (CNS) and pituitary of the lungfish, Protopterus annectens, by using antisera raised against UI from t he white sucker Catostomus commersoni and against UII from the goby Gillich ythys mirabilis. UI-like immunoreactive material was found within the melan otrope cells of the intermediate lobe of the pituitary. By contrast, no UI- immunoreactive structures were found in the brain. No UII-like peptides str ucturally similar to goby UII were found in the brain and pituitary of P. a nnectens. The UI-immunoreactive material localized in the pituitary was cha racterized by combining reversed-phase high-performance liquid chromatograp hy (HPLC) analysis and radioimmunological detection. The UI-like immunoreac tivity contained in a pituitary extract eluted as a single peak with a rete ntion time intermediate between those of sucker UI and rat corticotropin-re leasing factor (CRF). Control tests on adjacent sections of pituitary showe d that the UI antiserum cross-reacted with the frog skin peptide sauvagine, but lungfish UI did not co-elute with synthetic sauvagine on HPLC. On the contrary, no cross-reaction was observed between the UI antiserum and CRF o r alpha-melanocyte-stimulating hormone (alpha-MSH). The occurrence of an UI -like peptide in the intermediate lobe of the pituitary of P. annectens sug gests that, in lungfish, this peptide may act as a classic pituitary hormon e or may be involved in the control of melanotrope cell secretion. (C) 1999 Elsevier Science Inc. All rights reserved.