Prostaglandin E-2 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 mu l) into the ventromedial hypothalamus (VMH) on nociception were studie d using a hot-plate test in rats. Microinjection of PGE2 (5-500 pg and 50 n g/0.2 pi) into the VMH significantly prolonged the paw-withdrawal latency o n a hot plate 5 and 10 min after injection, respectively. Maximal prolongat ion was obtained 5 min after the injection of PGE? at 5 pg. Subsequently, t o determine whether the PGE2 receptor subtype EPI is involved in the PGE(2) -induced antinociceptive effect in the VMH, we observed the changes in noci ception after intraVMH microinjection of SC19220, an EPI receptor antagonis t, and 17-phenyl-omega-trinor PGE2, an EPI receptor agonist. Simultaneous i njection 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 int raVMH microinjection of 17-phenyl-omega-trinor PGE(2) (500 pg) prolonged it . These results indicate that PGE2 in the VMH has antinociceptive effect th rough its actions on EPI receptors in rats. (C) 1999 International Associat ion for the Study of Pain. Published by Elsevier Science B.V.