Interleukin-1 (IL-1) is one of the principal cytokines that participate in local regulation of many reproductive functions. The present study was undertaken to determine whether mRNAs for IL-1alpha, IL-1beta, and IL-1 type I receptor (IL-1R) are expressed in bovine corpora lutea (CL), and whether luteal cells respond to treatment with IL-1alpha and IL-1beta during the luteal phase. Bovine CL were classified into five stages (early, Days 2-3; developing, Days 5-6; mid, Days 8-12; late, Days 15-17; and regressed, Days 19-21). IL-1alpha, IL-1beta, and IL-1R mRNAs were detected by reverse transcription-polymerase chain reaction (PCR) in all luteal stages examined. Densitometric analysis of PCR products revealed increases of the mRNA of IL-1alpha and IL-1R in the CL of the regressed stage (P < 0.05). There was less mRNA for IL-1beta in the regressed stage than in the developing and mid stages (P < 0.05). When developing, mid, and late luteal cells were treated with IL-1alpha (1-30 ng/ml) or IL-1beta (1-30 ng/ml) for 24 h, IL-1alpha and IL-1beta dose-dependently increased prostaglandin (PG) F(2alpha) and PGE(2) production by the luteal cells of all stages (P < 0.05), indicating the presence of functional IL-1R in bovine CL. However, progesterone synthesis was not affected by either IL-1alpha or IL-1beta treatment. Stimulation with IL-1alpha and IL-1beta decreased the PGE(2):PGF(2alpha) ratio in the developing stage (P < 0.05), whereas it increased the ratio in the mid stage (P < 0.05). In the late stage, the ratio of IL-1beta-treated cells was greater than that of IL-1alpha-treated cells (P < 0.05). Overall results indicate that genes for IL-1alpha and IL-1beta are expressed and a functional IL-1R is present in the bovine CL throughout the luteal phase, and suggest that IL-1alpha and IL-1beta have different roles as local modulators to regulate PGF(2alpha) and PGE(2) production during the luteal phase.