PGE₂ production in gastric mucosa from control, COX1-deficient, and COX2-deficient animals. From left to right, the bars represent PGE₂ level in controls (n = 4), COX1 knockout mice (COX1^–/–, n = 10), mice pretreated with the COX1 inhibitor for 7 days (n = 8), mice receiving acute infusion of the COX1 inhibitor for 30 minutes (n = 11), COX2 knockout mice (n = 7), mice pretreated with the COX2 inhibitor for 7 days (n = 8), and mice receiving acute infusion of the COX2 inhibitor for 30 minutes (n = 12). P < 0.05 in all three groups with COX1 inhibition vs. controls, or vs. each group with COX2 inhibition.