peptide agonists produce activation of distinct signal transduction cascades from those of the lipid-derived transmitters suggesting that the functional consequences of CB1 activation are determined by the ligand. However, the relevance of these peptides for physiological processes is unclear, at present, and more work is needed to determine if the molecules are significant components of the EC system. Because these peptide ligands are derived from hemoglobin, it may be difficult to demonstrate that they are present in brain tissue and not an artifact from the homogenization of tissue along with the neurovasculature. Nevertheless, these findings indicate that our understanding of EC transmitters will continue to evolve as novel ligands and their associated synthetic pathways will likely be discovered.
