Endogenous opioids inhibit early-stage pancreatic pain in a mouse model of pancreatic cancer.
OBJECTIVE
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.
Sevcik
Molly A
MA
Neurosystems Center, Department of Diagnostic and Biological Sciences, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Jonas
Beth M
BM
Lindsay
Theodore H
TH
Halvorson
Kyle G
KG
Ghilardi
Joseph R
JR
Kuskowski
Michael A
MA
Mukherjee
Pinku
P
Maggio
John E
JE
Mantyh
Patrick W
PW
D015746:Abdominal Pain / Q000188:drug therapy* / Q000209:etiology / Q000378:metabolism; D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000627:therapeutic use*; D018847:Opioid Peptides / Q000627:therapeutic use*; D010147:Pain Measurement; D010190:Pancreatic Neoplasms / Q000150:complications* / Q000188:drug therapy / Q000473:pathology; D012720:Severity of Illness Index; D016896:Treatment Outcome
D009292:Narcotic Antagonists; D018377:Neurotransmitter Agents; D018847:Opioid Peptides; D009270:Naloxone