A novel hypothalamic neuroendocrine peptide: URP (urotensin-II-related peptide)?

Urotensin-II-related peptide (URP) is an eight-amino-acid peptide recently isolated from rat brain and considered as the endogenous ligand for the urotensin-II receptor. Immunohistochemical treatment of mouse brain sections with anti-URP antibodies revealed numerous immunopositive fibres in the median eminence and vascular organ of the lamina terminalis as well as labelled cell bodies, mainly in the preoptic area. In consecutive serial sections, in situ hybridization demonstrated URP-mRNA in neuronal perikarya. Double-immunofluorescence labelling showed a co-localization of URP and GnRH in fibres and cell bodies. These results suggest the existence of URP as a novel hypothalamic neuroendocrine peptide co-localized and possible co-released with GnRH.