Intrathecal administration of prostaglandin E2 causes sensitization of the primary afferent neuron via the spinal release of glutamate

The effects of S- and R-flurbiprofen on the inflammation-evoked intraspinal release of immunoreactive substance P--a study with antibody microprobes

Using antibody coated microprobes in anesthetized rats, we studied the intraspinal release of immunoreactive substance P during development of kaolin/carrageenan-induced inflammation in the knee joint, and the effects of S- and R-flurbiprofen on inflammation-evoked intraspinal release of immunoreactive substance P once inflammation was established. During the first 6 h after induction of acute inflammation, the basal release and the release of immunoreactive substance P evoked by innocuous pressure applied to the knee showed increases (n=4 rats). An intravenous dose of 9 mg/kg S-flurbiprofen (a potent inhibitor of cyclooxygenases that is anti-inflammatory and antinociceptive) did not significantly alter the pattern of inflammation-evoked release of immunoreactive substance P within 2 h although this dose reduced the responses of spinal cord neurons to pressure applied to the inflamed knee joint within 15 min to about 15% of the predrug value (Neugebauer et al., J. Pharmacol. Exp. Ther. 275 (1995) 618-628). The subsequent i.v. injection of 27 mg/kg S-flurbiprofen significantly changed the pattern of release of immunoreactive substance P showing a reduction of the level of immunoreactive substance P in the dorsal horn within 1 h (n=4 rats). The release of immunoreactive substance P was also reduced after the i.v. injection of 27 mg/kg R-flurbiprofen that is also antinociceptive but less anti-inflammatory (n=5 rats). These data show that both S- and R-flurbiprofen reduce the inflammation-evoked intraspinal release of immunoreactive substance P within hours. However, the reduction of release of immunoreactive substance P does not seem to be a prerequisite for the initial antinociceptive action of non-steroidal anti-inflammatory drugs. It may be rather important in the long term range.

Cyclooxygenases 1 and 2

Cyclooxygenase (COX), first purified in 1976 and cloned in 1988, is the key enzyme in the synthesis of prostaglandins (PGs) from arachidonic acid. In 1991, several laboratories identified a product from a second gene with COX activity and called it COX-2. However, COX-2 was inducible, and the inducing stimuli included pro-inflammatory cytokines and growth factors, implying a role for COX-2 in both inflammation and control of cell growth. The two isoforms of COX are almost identical in structure but have important differences in substrate and inhibitor selectivity and in their intracellular locations. Protective PGs, which preserve the integrity of the stomach lining and maintain normal renal function in a compromised kidney, are synthesized by COX-1. In addition to the induction of COX-2 in inflammatory lesions, it is present constitutively in the brain and spinal cord, where it may be involved in nerve transmission, particularly that for pain and fever. PGs made by COX-2 are also important in ovulation and in the birth process. The discovery of COX-2 has made possible the design of drugs that reduce inflammation without removing the protective PGs in the stomach and kidney made by COX-1. These highly selective COX-2 inhibitors may not only be anti-inflammatory but may also be active in colon cancer and Alzheimer's disease.

Peripheral noxious stimulation releases spinal PGE2 during the first phase in the formalin assay of the rat

Injection of formalin (5%; 50 microl) into the dorsal surface of the hind paw of rats evoked a characteristic biphasic flinching behaviour of the injured paw accompanied by a significant increase in the interstitial prostaglandin E2 (PGE2) concentration of the dorsal lumbar spinal cord. Interestingly, the increase in PGE2 concentration was only observed during the first phase of the formalin behavioural response (during the 0-10 and 10-20 min microdialysis-sample). Saline paw injection did not have a significant effect on behaviour or on PGE2 concentration. These data suggest that spinal release of PGE2 is involved in nociceptive processing in the formalin-induced hyperalgesia model of the rat during the first but not second phase.