PROBLEM: Uterine infection occurs in as much as 20% of preterm labor and results in increased decidual cytokines. The objective of this study was to examine the effect of interleukin-1 (IL-1) and the cyclooxygenase-2 (COX-2) inhibitor, NS-398, on myometrial prostaglandin (PG) production and COX-2 expression. METHOD OF STUDY: Human uterine myocytes were stimulated with IL-1 (0-50 ng/ml) over 24 hr. PGE2, PGF(2α), and 6-keto F(1α) were measured by enzyme-linked immunosorbent assay. Both COX-1 and COX-2 proteins and mRNA were measured by western and northern blot, respectively. RESULTS: IL-1 increased PG production beginning at 6 hr. COX-2 protein increased beginning at 4 hr and continued to increase at 24 hr. COX-2 mRNA increased at 2 hr and peaked at 4 hr. NS-398 blocked PG production but had no effect on COX-2 protein or mRNA. CONCLUSIONS: IL-1 increases PG production by myometrium by increased COX-2 expression. NS-398 completely blocks IL-1-induced PG production. With intrauterine infection, IL-1 may induce labor through the autocrine production of uterotonic PGs.