AT1 receptor antagonism enhances angiotensin-II-facilitated carrageenan-induced paw edema.

Recent studies have demonstrated that the renin-angiotensin system (RAS) participates in the processes of inflammation. An active component of this system, angiotensin II (Ang II), differentially regulates the production of oxyradicals, nitric oxide, prostaglandins, platelet-activating factors and bradykinins by acting through AT1 or AT2 receptor subtypes. Many of the physiological actions of Ang II mediated through AT1 and AT2 receptors are opposite and thereby show physiological antagonism to each other. In the present study, we evaluated the effect of locally administered Ang II, the ACE inhibitor captopril and the AT1 receptor antagonist losartan in the carrageenan model of acute inflammation. Local administration of losartan (10-50 micrograms/paw) or Ang II (0.2-1 microgram/paw) alone did not induce inflammation, but significantly enhanced the carrageenan-induced edema in a dose-dependent manner. Coadministration of subeffective doses of losartan (10 micrograms/paw) and Ang II (0.2 microgram/paw) significantly potentiated the carrageenan-induced inflammation. In conclusion, the present study predicts that Ang II might be formed locally during carrageenan-induced acute inflammation. Potentiation of the Ang II effect in carrageenan-induced inflammation by losartan may be mediated through over-stimulation of unblocked AT2 receptors or due to stimulation of inflammatory pathways by unknown mechanisms.