Endogenous opioids inhibit early-stage pancreatic pain in a mouse model of pancreatic cancer

Gastroenterology. 2006 Sep;131(3):900-10. doi: 10.1053/j.gastro.2006.06.021.

Abstract

Background & aims: The endogenous opioid system is involved in modulating the experience of pain, the response to stress, and the action of analgesic therapies. Recent human imaging studies have shown a significant tonic modulation of visceral pain, raising the question of whether endogenous opioids tonically modulate the pain of visceral cancer.

Methods: Transgenic mice expressing the first 127 amino acids of simian virus 40 large T antigen, under the control of the rat elastase-1 promoter, that spontaneously develop pancreatic cancer were used to investigate the role of endogenous opioids in the modulation of pancreatic cancer pain. Visceral pain behaviors were assessed as degree of hunching and vocalization.

Results: Although mice with late-stage pancreatic cancer displayed spontaneous, morphine-reversible, visceral pain-related behaviors such as hunching and vocalization, these behaviors were absent in mice with early-stage pancreatic cancer. After systemic administration of the central nervous system (CNS)-penetrant opioid receptor antagonists naloxone or naltrexone, mice with early-stage pancreatic cancer displayed significant visceral pain-related behaviors, whereas systemic administration of the CNS-nonpenetrant opioid antagonist naloxone-methiodide did not induce an increase in visceral pain behaviors.

Conclusions: Our findings suggest that a CNS opioid-dependent mechanism tonically modulates early and late-stage pancreatic cancer pain. Understanding the mechanisms that mask this pain in early stage disease and drive this pain in late-stage disease may allow improved diagnosis, treatment, and care of patients with pancreatic cancer.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Abdominal Pain / drug therapy*
  • Abdominal Pain / etiology
  • Abdominal Pain / metabolism
  • Animals
  • Disease Models, Animal
  • Female
  • Immunohistochemistry
  • Male
  • Mice
  • Naloxone / pharmacology
  • Narcotic Antagonists / pharmacology
  • Neurotransmitter Agents / therapeutic use*
  • Opioid Peptides / therapeutic use*
  • Pain Measurement
  • Pancreatic Neoplasms / complications*
  • Pancreatic Neoplasms / drug therapy
  • Pancreatic Neoplasms / pathology
  • Severity of Illness Index
  • Treatment Outcome

Substances

  • Narcotic Antagonists
  • Neurotransmitter Agents
  • Opioid Peptides
  • Naloxone