Increasing evidence indicates that PGs may play an obligatory role in blastocyst implantation. Cyclooxygenase (also known as PGH synthase) isozymes 1 and 2 catalyze the rate limiting steps in the biosynthesis of PGs. The ubiquitous cyclooxygenase-1 (COX-1) subserves housekeeping functions, whereas the inducible cyclooxygenase-2 (COX-2) is expressed by limited cell types and tightly controlled. Here we report the induction of COX-2 gene expression by interleukin-1 beta (IL-1 beta) in cultured human endometrial stromal cells. COX-2 activity was induced by IL-1 beta (1 ng/mL); conversion of exogenous arachidonic acid to PGF2 alpha increased from 2.6 +/- 0.6 ng/well (mean +/- SEM; n = 6) to 22.2 +/- 5.6 ng, but was completely blocked (2.8 +/- 0.7 ng/well) by NS-398, a specific COX-2 inhibitor. Undetectable in quiescent stromal cells, messenger ribonucleic acid for COX-2 was induced 30 min after IL-1 beta treatment, reached a maximum at 4 h, and decreased after 15 h. Protein synthesis was not required for induction of the COX-2 gene, as it was blocked by actinomycin D but not by cycloheximide. The 70-kDa COX-2 protein was not detected in quiescent cells, became detectable 6 h after IL-1 beta treatment, and remained detectable even after 15 h. IL-1 beta (0.1-100 ng/mL) increased the luciferase activity in promoterless luciferase reporter containing the 900-bp 5'-flanking sequence (-891 to +9) of the COX-2 gene in a dose-dependent manner, with an ED50 of 0.1-1 ng/mL.