Induction of opioid tolerance by lysine-acetylsalicylate in rats
by
Pernia-Andrade AJ, Tortorici V, Vanegas H.
Instituto Venezolano de Investigaciones Cientificas,
Apartado 21827, Caracas 1020A, Venezuela.
Pain. 2004 Sep;111(1-2):191-200.

ABSTRACT

The analgesic effect of non-steroidal antiinflammatory drugs (NSAIDs) is due to their action upon the peripheral damaged tissues, the spinal cord, and brain stem structures of the 'descending pain-control system' such as the periaqueductal gray matter (PAG) and the nucleus raphe magnus (NRM). The NSAID dipyrone (metamizol) has been shown to engage opioidergic circuits at the PAG, the NRM and the spinal cord, but it is unknown whether this can be generalized to typical NSAIDs and to systemic administration. In the present study lysine-acetylsalicylate (LASA), an injectable form of the prototypical NSAID aspirin, was microinjected into the PAG (100 microg/0.5 microl) in freely moving rats to induce inhibition of tail flick and hot plate responses. This antinociception was reverted by naloxone (1 mg/kg i.p.). PAG microinjection of LASA twice daily for three days induced tolerance to LASA (i.e. a progressive loss of effectiveness) and cross-tolerance to PAG-microinjected morphine (5 microg/0.5 microl). The antinociceptive effect of systemically administered LASA (300 mg/kg i.p., equivalent to the 1000 mg analgesic dose for humans) was also abolished by naloxone. Intraperitoneal injection of LASA twice daily induced tolerance to LASA and cross-tolerance to i.p. morphine (1 or 5 mg/kg). LASA-tolerant rats showed opioid withdrawal signs when injected with naloxone. These findings support the notion that the contribution of the PAG and downstream pain-control structures to the analgesic effect of NSAIDs involves opioidergic mechanisms, and suggest that repeated therapeutic administration of NSAIDs may induce tolerance, cross-tolerance to opiates, and susceptibility to a withdrawal syndrome.

Pain
DAMGO
Arrestin
G protein
Nocistatin
Mechanisms
Opioids for the old
Receptor regulation
Glycine anatagonists
Drugs to prevent opioid tolerance
The molecular mechanisms of opioid tolerance
Morphine-induced changes of gene expression
Anxiety, opioids, cholecystokinin and tolerance
Non-opioid tolerance and endogenous opioid system

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