Prostaglandin E2 has antinociceptive effect through EP1 receptor in the ventromedial hypothalamus in rats

The effects of microinjection of prostaglandin E(2) (PGE(2)) (50 fg-50 ng/0.2 microl) into the ventromedial hypothalamus (VMH) on nociception were studied using a hot-plate test in rats. Microinjection of PGE(2) (5-500 pg and 50 ng/0.2 microl) into the VMH significantly prolonged the paw-withdrawal latency on a hot plate 5 and 10 min after injection, respectively. Maximal prolongation was obtained 5 min after the injection of PGE(2) at 5 pg. Subsequently, to determine whether the PGE(2) receptor subtype EP(1) is involved in the PGE(2)-induced antinociceptive effect in the VMH, we observed the changes in nociception after intraVMH microinjection of SC19220, an EP(1) receptor antagonist, and 17-phenyl-omega-trinor PGE(2), an EP(1) receptor agonist. Simultaneous injection of SC19220 (150 ng) with PGE(2) (500 pg) into the VMH blocked the PGE(2)-induced prolongation of the paw-withdrawal latency. Moreover, an intraVMH microinjection of 17-phenyl-omega-trinor PGE(2) (500 pg) prolonged it. These results indicate that PGE(2) in the VMH has antinociceptive effect through its actions on EP(1) receptors in rats.