AN I-2 IMIDAZOLINE LIGAND, RS-45041, POTENTIATES HYPERALGESIA IN ACUTE ARTHRITIS

DESCENDING inhibition is increased after the induction of inflammation of the knee. The present study investigated whether this effect is me diated through alpha(2)-adrenoceptors and/or I-2 imidazoline receptors in the rat. An alpha(2)-adrenoceptor antagonist, RX 821002, a selecti ve I-2 imidazoline ligand, RS 45041, and idazoxan, which has affinity for both these receptor types, were administered. After the induction of acute arthritis by intra-articular injection of kaolin and carragee nan, the agents binding to I-2 imidazoline receptors further reduced t he paw withdrawal latency to radiant heat beyond that induced by acute arthritis, i.e. these drugs were pronociceptive, potentiating hyperal gesia. These results suggest that I-2 imidazoline receptors have an im portant role to play in modulation of hyperalgesia during acute inflam mation. Development of I-2 imidazoline drugs may prove useful in the t reatment of hyperalgesia.