Macula densa cyclooxygenase 2 (COX-2)-derived prostaglandins serve as important modulators of the renin-angiotensin system, and cross-talk exists between these two systems. Cortical COX-2 induction by angiotensin-converting enzyme (ACE) inhibitors or AT ₁ receptor blockers (ARBs) suggests that angiotensin II may inhibit cortical COX-2 by stimulating the AT ₁ receptor pathway. In the present studies we determined that chronic infusion of either hypertensive or nonhypertensive concentrations of angiotensin II attenuated cortical COX-2. Angiotensin II infusion reversed cortical COX-2 elevation induced by ACE inhibitors. However, we found that angiotensin II infusion further stimulated cortical COX-2 elevation induced by ARBs, suggesting a potential role for an AT ₂ receptor-mediated pathway when the AT ₁ receptor was inhibited. Both WT and AT ₂ receptor knockout mice were treated for 7 days with either ACE inhibitors or ARBs. Cortical COX-2 increased to similar levels in response to ACE inhibition in both knockout and WT mice. In WT mice ARBs increased cortical COX-2 more than ACE inhibitors, and this stimulation was attenuated by the AT ₂ receptor antagonist PD123319. In the knockout mice ARBs led to significantly less cortical COX-2 elevation, which was not attenuated by PD123319. PCR confirmed AT _1a and AT ₂ receptor expression in the cultured macula densa cell line MMDD1. Angiotensin II inhibited MMDD1 COX-2, and CGP42112A, an AT ₂ receptor agonist, stimulated MMDD1 COX-2. In summary, these results demonstrate that macula densa COX-2 expression is oppositely regulated by AT ₁ and AT ₂ receptors and suggest that AT ₂ receptor-mediated cortical COX-2 elevation may mediate physiologic effects that modulate AT ₁ -mediated responses.