ANTINOCICEPTIVE EFFECT OF SPINALLY DELIVERED PROSTAGLANDIN-E RECEPTORANTAGONISTS IN THE FORMALIN TEST ON THE RAT

The antinociceptive effect of spinally administered prostaglandin E(2) receptor antagonists, SC-51089 and SC-51234A, which are selective for EP1 receptors, was examined in rats using the formalin test. Intrathe cal injection of SC-51089 (30-300 mu g) or SC-51234A (30-300 mu g) res ulted in a significant, dose-dependent, suppression of the second phas e (10-60 min), but not the first phase (0-9 min), flinching behavior e voked by formalin injection into the paw. ED(25) values and 95% confid ence intervals for the second phase were 120 (70-200) mu g for SC-5108 9 and 80 (50-140) mu g for SC-51234A. These data demonstrate that spec ific nociceptive behaviors are attenuated by spinal prostaglandin E(2) receptor antagonists and suggest that prostaglandin E(2) is involved in facilitated processing at the spinal level.