CXCL1, CXCL1-Ab or Hexapeptide alone does not affect rat tail-flick latency throughout 120 h infusion. CXCL1 (1.2 ng/h), CXCL1-Ab (3.6 ng/h), hexapeptide (5 μg/h), morphine (15 μg/h), and saline control were individually infused intrathecally via osmotic minipump. Tail-flick latency responses (s) were observed at 0, 4, 16, 24, 48, 72, 96, and 120 h. Morphine analgesic efficacy peaked at 16 h and gradually declined. None of the other infused substances affected tail-flick latency.