The fish neuropeptide urotensin I: its physiology and pharmacology

Significant structural and biological homologies between urotensin I (UI), ovine hypothalamic corticotropin releasing factor (oCRF) and the frog skin peptide sauvagine (SVG) have been investigated and compared in fishes and mammals. In mammals, urotensin and the related peptides exert uniquely selective mesenteric vasodilatation, oCRF having approximately equal to 4% the activity of the other two. All three peptides are equipotent in stimulation of ACTH secretion in the rat in vivo and in vitro. UI is significantly more potent than the other two related peptides in stimulation of ACTH secretion in the goldfish pituitary. Immunocytochemical demonstration of UI not only in the caudal spinal cord but also in the brain, mainly in the lateral tuberal region and of an oCRF-like substance in the preoptic nucleus and pituitary, suggests that ACTH secretion in fishes may be controlled by two similar but distinct UI- or oCRF-like peptides.