Recent advances in peptidomics have enabled the identification of previously uncharacterized
peptides. However, sequence information alone does not allow us to identify candidates for bioactive
peptides. To increase an opportunity to discover bioactive
peptides, we have focused on C-terminal amidation, a post-translational modification shared by many bioactive
peptides. We analyzed
peptides secreted from human medullary
thyroid carcinoma TT cells that produce amidated
peptides, and we identified two novel amidated
peptides, designated neuroendocrine regulatory
peptide (NERP)-1 and NERP-2. NERPs are derived from distinct regions of the neurosecretory
protein that was originally identified as a product of a
nerve growth factor-responsive gene in PC12 cells. Mass spectrometric analysis of the immunoprecipitate using specific
antibodies as well as reversed phase-high performance liquid chromatography coupled with radioimmunoassay analysis of brain extract demonstrated the endogenous presence of NERP-1 and NERP-2 in the rat. NERPs are abundant in the paraventricular and supraoptic nuclei of the rat hypothalamus and colocalized frequently with
vasopressin but rarely with
oxytocin. NERPs dose-dependently suppressed
vasopressin release induced by intracerebroventricular injection of hypertonic NaCl or
angiotensin II in vivo. NERPs also suppressed basal and
angiotensin II-induced
vasopressin secretion from hypothalamic explants in vitro. Bioactivity of NERPs required C-terminal amidation. Anti-NERP IgGs canceled plasma
vasopressin reduction in response to water loading, indicating that NERPs could be potent endogenous suppressors of
vasopressin release. These findings suggest that NERPs are novel modulators in body fluid homeostasis.