We examined effects of interleukin 1α (IL1α) and phorbol 12, 13 dibutyrate (PDB), an activator of protein kinase C, on mRNA for Prostaglandin H synthase (PGHS) and prostanoid production in cultured ovine meningeal fibroblasts. Immuno- and morphologically-identified fibroblasts were derived from cerebral cortex and white matter from fetal lambs (approximately 120 days gestation) and grown to confluence on glass coverslips in 12 well plates. Levels of prostaglandin F2α and the stable hydrolysis product of prostacyclin (i.e., 6-keto-PGF1α) were determined using enzyme immunoassay. Relative amounts of mRNA were determined by in situ hybridization using ovine cDNA for PGHS1. IL1α (10 ng/ml) increased mRNA levels over baseline by 62⁑19% (p＜0.05) at 60 min., 37⁑12% (NS) at 120 min., and 36⁑18% (NS) at 240 min (n=12). Levels of 6-keto-PGF1α were 148⁑18 pg/ml during baseline, 246⁑41 pg/ml at 60 min., 248⁑40 pg/ml at 120 min., and 259⁑62 pg/ml at 240 min (all p＜0.05) (n=12). PGF2α was increased although it wasn't statistically significant. However, IL1α decreased PGE2 level significantly (all p＜0.05). PDB (10⁣6M) increased mRNA levels over baseline by 25⁑6% after 30 min., 40⁑6% after 60 min., and 20⁑8% after 90 min. (n=9) (all p＜0.05). Levels of 6-keto-PGF1α were 200⁑43 pg/ml during baseline, 202⁑43 pg/ml after 30 min. (NS), 268⁑58 pg/ml after 60 min. (p＜0.05), and 296⁑60 pg/ml after 90 min. (p＜0.05) (n=9). Levels of PGF2α were 178⁑26 pg/ml during baseline, 300⁑30 pg/ml after 30 min., 299⁑35 pg/ml after 60 min., and 355⁑32 pg/ml after 90 min (all p＜0.05) (n=6). Actinomycin-D (1 mg/ml) prevented increases in mRNA, 6-keto-PGF1α, and PGF2α at 60 min. for both IL1α and PDB. We conclude that cerebral fibroblasts are avid producers of prostanoids, and that enhanced production of PGHS is responsible for augmented PGF2α and prostacyclin production in the presence of an activator of protein kinase C and for decreased PGE2 and increased prostacyclin production in the presence of IL1α.