A hemoglobin fragment found in cervicovaginal fluid from women in labor potentiates the action of agents that promote contraction of smooth muscle cells

We employed a proteomic approach to search for peptides that have a physiological role in labor. Cervicovaginal secretions were collected at term from women in labor and women at term not in labor. Samples were spotted onto weak cation exchange chips (WCX-2) and analyzed using Surface-Enhanced Laser Desorption Ionization Time-of-Flight Mass Spectrometry (SELDI-TOF-MS). Spectra were obtained for each sample and Biomarker Wizard analysis revealed 25 peaks that had significantly different peak intensity between the labor and non-laboring women. The sequences of five peaks that were significantly elevated in the labor cohort were determined using Protein Chip Interface Quadruple Time-of-Flight Mass Spectrometry (PCI-QTOF-MS). All of these peaks were identified as fragments of α or β-hemoglobin (Hb). A 2.022 kDa fragment of α-Hb (amino acids 110–128, NH2-AAHLPAEFTPAVHASLDKF-COOH) was found to potentiate smooth muscle cell contraction in response to bradykinin, oxytocin and prostaglandin-F2α. This peptide may promote vasoconstriction and augment normal labor through enhancing the action of uterotonins.