Intracerebroventricular injection of prostaglandin E2 induces thermal hyperalgesia in rats: the possible involvement of EP3 receptors.

To determine what types of prostanoid receptors are involved in the central effect of prostaglandin E2 (PGE2) on nociception, we administered PGE2 and its agonists, i.e., 17-phenyl-omega-trinor PGE2 (an EP1 receptor agonist), butaprost (an EP2 receptor agonist), 11-deoxy PGE1 (an EP2/EP3 receptor agonist, EP2 >> EP3) and M&B28767 (an EP3 receptor agonist) into the lateral cerebroventricle (LCV) of rats and observed the changes of paw-withdrawal latency on a hot plate. The LCV injection of PGE2 (10 pg/kg-10 ng/kg), 11-deoxy PGE1 (100 pg/kg-10 ng/kg) and M&B28767 (1 pg/kg-100 pg/kg) produced a significant reduction in the paw-withdrawal latency. The maximal reduction was observed 15 min after the LCV injection of these drugs. Neither 17-phenyl-omega-trinor PGE2 (1 pg/kg-1 microgram/kg) nor butaprost (1 pg/kg-100 microgram/kg) induced any significant changes in the paw-withdrawal latency. The LCV injection of PGE2 (1 microgram/kg) and 17-phenyl-omega-trinor PGE2 (50 micrograms/kg) increased the latency only 5 min after LCV injection. These findings indicate that the LCV injection of PGE2 induces thermal hyperalgesia through EP3 receptors and analgesia through EP1 receptors by its central action in rats.