Thromboxane A2 is Involved in Itch-associated Responses in Mice with Atopic Dermatitis-like Skin Lesions

To investigate the mechanisms underlying itching in atopic dermatitis, we examined whether thromboxane (TX) A2, an arachidonic acid metabolite, is involved in spontaneous scratching, an itch-related response, in NC mice with atopic dermatitis-like skin lesions. The TXA2 receptor (TP) antagonist ONO-3708 inhibited the spontaneous scratching. The mRNA expression of TX synthase (TXSyn) distributed mainly in epidermis and the concentration of TXB2, a metabolite of TXA2, were increased in lesional skin. Scratching caused by the PAR2 agonist SLIGRL-NH2 was suppressed by ONO-3708. SLIGRL-NH2-induced scratching decreased approximately 75% in TP-deficient mice, compared to wild-type mice. In primary cultures of mouse keratinocytes, SLIGRL-NH2 induced the production of TXA2, as evidenced by the increased TXB2, which was inhibited by the TXSyn inhibitor sodium ozagrel and a PAR2-neutralizing antibody. Taken together, these results suggest that epidermal TXA2, which may be produced via PAR2 activation, is involved in itching in atopic dermatitis

Decreased susceptibility to renovascular hypertension in mice lacking the prostaglandin I(2) receptor IP

Persistent reduction of renal perfusion pressure induces renovascular hypertension by activating the renin-angiotensin-aldosterone system; however, the sensing mechanism remains elusive. Here we investigated the role of PGI(2) in renovascular hypertension in vivo, employing mice lacking the PGI(2) receptor (IP(–/–) mice). In WT mice with a two-kidney, one-clip model of renovascular hypertension, the BP was significantly elevated. The increase in BP in IP(–/–) mice, however, was significantly lower than that in WT mice. Similarly, the increases in plasma renin activity, renal renin mRNA, and plasma aldosterone in response to renal artery stenosis were all significantly lower in IP(–/–) mice than in WT mice. All these parameters were measured in mice lacking the four PGE(2) receptor subtypes individually, and we found that these mice had similar responses to WT mice. PGI(2) is produced by COX-2 and a selective inhibitor of this enzyme, SC-58125, also significantly reduced the increases in plasma renin activity and renin mRNA expression in WT mice with renal artery stenosis, but these effects were absent in IP(–/–) mice. When the renin-angiotensin-aldosterone system was activated by salt depletion, SC-58125 blunted the response in WT mice but not in IP(–/–) mice. These results indicate that PGI(2) derived from COX-2 plays a critical role in regulating the release of renin and consequently renovascular hypertension in vivo