Effect of the inhibition of serotonin biosynthesis on the antinociception induced by nonsteroidal anti-inflammatory drugs

The antinociceptive activity of nonsteroidal anti-inflammatory drugs (NSAIDs) has been explained mainly on the basis of their inhibition of the enzyme cyclooxygenase (COX); however, this inhibition is not enough to completely explain the analgesic efficacy of these drugs. The modulation exerted by serotonergic systems on antinociception is well known. The purpose of the present work was to further explore the role of serotonin in the antinociceptive activity of NSAIDs using the writhing test and the tail-flick test of the mice after the inhibition of serotonin biosynthesis with intraperitoneal p-chlorophenylalanine (p-CPA). Pretreatment with p-CPA produced a significant decrease in the antinociceptive activity of NSAIDs administered either by the intraperitoneal or intrathecal routes, in both algesiometric tests. These results suggest a complementary mechanism of antinociception for NSAIDs, independent of their ability to inhibit the activity of COX, involving the activation of descending serotonergic pathways. By the pharmacological nature of the study, one limitation was the absence of biochemical measurement of the synthesis of 5-HT, since the reduction of the brain 5-HT synthesis by pretreatment with p-CPA will be expressed as a disminished antinociceptive activity of NSAIDs, which would be a new argument to consider NSAIDs acting as central analgesic agents.