Role of EP4 receptors in local and systemic inflammatory responses. (a) Detection of EP4 receptor mRNA by RT-PCR in diseased EP4+/+ liver. (b) Total RNA was extracted from EP4+/+ and EP4–/– normal and diseased livers, followed by IL-1β/GAPDH determinations as described in Methods. EP4+/+, 36.4 ± 6.7 (n = 4); and EP4–/–, 34.9 ± 8.2 (n = 4), in arbitrary units (IL-1β pg RNA/GAPDH pg RNA). In contrast, levels were significantly different in diseased liver samples: EP4+/+, 57.4 ± 4.4 (n = 4) and EP4–/–, 20.6 ± 2.7 (n = 4). *P < 0.05 by two-way ANOVA. (c) Detection of EP4 receptor mRNA by RT-PCR from diseased wild-type peritoneal macrophages. (d) Determination of IL-6 (ng/ml) secreted from peritoneal macrophages isolated from diseased EP4+/+ and EP4–/– mice. Media only: EP4+/+, 8.6 ± 0.1 (n = 3); EP4–/–, 5.4 ± 0.1 (n = 3). LPS (1 μg/ml): EP4+/+, 12.9 ± 0.5 (n = 3); EP4–/–, 13.5 ± 0.7 (n = 3). *P < 0.05, by two-way ANOVA. In b and d, black bars are results from EP4+/+ animals and white bars are results from EP4–/– animals. OD β hex, β-hexasiminadase activity.