Differential Analgesic Effects of Aspirin-like Drugs

Tissue damage, including that due to surgical manipulation, results in 2 distinct but connected changes in the pain perception pathway. Firstly, cells disintegrate at the site of tissue damage and release mediators, including prostaglandins. These mediators transform fine nerve endings, particularly high-threshold mechanoceptors, into nociceptors. In other words, fine nerve endings that are not normally activated by mechanical pressure or temperature changes become very sensitive and are depolarised after minor mechanical or thermal changes. Secondly, in the central nervous system (CNS) and, particularly, in the dorsal horn of the spinal cord, reflex activity is increased, metabolic activity of the neuronal cells is enhanced and, chronically, major rearrangements of mediator production and electrical activity of the dorsal horn cells may be observed. Both types of change contribute to the well known phenomenon of hyperalgesia, which is regularly observed in connection with tissue damage, including that produced by surgical manipulation. It has been shown that aspirin-like drugs reduce the enhanced nociceptor activity in damaged tissue, probably as a result of prostaglandin synthesis inhibition. Recently, there have been indications that these drugs may have an additional mechanism of action in the spinal cord or higher parts of the CNS. Using the pure enantiomers of flurbiprofen in pharmacodynamic experiments in the rat, we have observed that the R- and S-enantiomers may exert differential analgesic effects. The R-enantiomer, which does not inhibit cyclo-oxygenase in vitro, was almost as effective as the S-enantiomer, which does inhibit prostaglandin synthesis in different models of pain and nociception.(ABSTRACT TRUNCATED AT 250 WORDS)