Thromboxane A2 induces itch-associated responses through TP receptors in the skin in mice

Thromboxane A(2) (TXA(2)), a metabolite of arachidonic acid produced by cyclooxygenase and thromboxane synthase, is thought to participate in chronic dermatitis. This study investigated the involvement of TXA(2) in cutaneous itch. An intradermal injection of U-46619, a stable analogue of TXA(2), elicited scratching, an itchassociated response, in mice. Dose-response curve was bell shaped with a maximum effect at 10 nmol per site. The action of U-46619 was inhibited by a coinjection of the TP antagonist ONO-3708 and was abolished by TP receptor deficiency. TP receptor was mainly expressed in nerve fiber in the skin and keratinocytes. Thromboxane synthase was also expressed in keratinocytes. U-46619 increased intracellular Ca2+ ion concentration in primary cultures of dorsal root ganglion neurons and keratinocytes. The results suggest that TXA(2) synthesized by keratinocytes acts as an itch mediator. It may elicit itch through the activation of TP receptors on primary afferents and keratinocytes; keratinocytes may produce itch mediators including TXA(2). Thus, thromboxane synthase inhibitor and TP receptor antagonists will be candidates for antipruritic medicines.