Non-opioid peptides for analgesia.

Amongst the spinal peptide candidates believed to be involved in the mediation of analgesia, only somatostatin fulfills the criterium of a real analgesia substance. Spinal somatostatin specifically blocks the transmission of painful stimuli. Spinal calcitonin may lower the opioid dose requirement in patients with bone metastases but it fails to relieve acute pain. The usefulness of ACTH and CRF for treatment of pain remains to be established. The role of CCK-8, vasopressin and neurotensin is unclear. The contradictory findings on antinociception using simple rodent withdrawal reflex tests (e.g. the tail flick test), or more complex behavioral tests in which supraspinal sensory processing is involved, (e.g. the hot plate test), indicate that these tests are inappropriate when neuropeptides are employed. Furthermore, due to their inability to predict analgesia in humans, they do not fulfill the guidelines proposed by the IASP that animal test procedures have to be for the benefit of humans.