Prostanoids are important regulators of ovarian function, especially during ovulation and luteolysis. Cyclooxygenase (Cox) is the rate-limiting enzyme in conversion of arachidonic acid to prostanoids. We have examined the expression and regulation of the inducible Cox isoform (Cox-2) and of the receptor for PGF2alpha (FP) in human granulosa cells obtained from women undergoing oocyte retrieval for in vitro fertilization. Freshly isolated granulosa cells express Cox-2 and FP receptor messenger RNAs (mRNAs). FP receptor mRNA is also expressed in cultured human granulosa-luteal (GL) cells, but Cox-2 transcripts are expressed only upon induction. Interleukin-1beta (IL-1beta) elevated Cox-2 mRNA steady state levels in a concentration-dependent manner, and kinetic studies showed that Cox-2 mRNA levels were already induced at the 2 h point and returned to the basal level after incubation for 24 h. The protein synthesis inhibitor, cycloheximide, induced Cox-2 mRNA expression and potentiated the effect of IL-1beta. Degradation of Cox-2 mRNA was inhibited by IL-1beta, which suggests regulation at the posttranscriptional level. IL-1beta also induced the expression of Cox-2 protein, as detected by immunofluorescence staining using Cox-2-specific polyclonal antibodies. Further, IL-1beta-induced synthesis of prostanoids was blocked by a Cox-2-specific inhibitor, NS-398. In addition, hCG induced Cox-2 mRNA expression and potentiated the effect of IL-1beta. However, in contrast to the rapid and transient effect of IL-1beta on Cox-2 mRNA, the effect of hCG followed slower kinetics. We have previously shown that hCG induces expression of human FP receptor mRNA in cultured human GL cells. We now show that IL-1beta induces FP receptor mRNA in a time- and concentration-dependent manner. Our data suggest that Cox-2 and FP receptor are coexpressed in freshly isolated human granulosa cells and that their expression is up-regulated by IL-1beta and hCG in cultured human GL cells.