Cytokines are thought to regulate prostaglandin (PG) secretion in the bovine endometrium. However, there is no consensus about the role of interleukin-1alpha (IL1A) on PG secretion. The objective of this study was to examine the influence of IL1A on basal and interferon-tau (IFNT)-regulated PG in vitro secretion, as well its effects on PG secretion, progesterone (P(4)) output, and corpus luteum (CL) in vivo lifespan. Explants of bovine endometrium (days 16-17 of the estrous cycle or early pregnancy) were stimulated with IL1A (10 ng/ml), IFNT (30 ng/ml), or IL1A combined with IFN. IL1A alone strongly stimulated luteotrophic PGE(2) secretion by endometrial tissues of both pregnant and nonpregnant cows. IL1A also stimulated luteolytic PGF(2alpha) output in the late luteal phase. IFNT augmented the stimulatory effect of IL1A on PGE(2) secretion. In an in vivo experiment, saline or IL1A at different doses (0.001-10 microg/per animal) was applied to the uterine lumen on day 16 of the cycle. Only the highest dose of IL1A caused a temporal increase in PGF(2alpha) secretion, while it had no effect on P(4) secretion or CL lifespan. Application of 0.1 and 1 microg IL1A stimulated P(4) and PGE(2) output and prolonged the CL lifespan. Although IL1A may stimulate in vitro luteolytic PGF(2alpha) secretion during the estrous cycle, it only acts as a luteotrophic factor in vivo. IL1A increased luteotrophic PGE(2) and P(4) output, inhibiting spontaneous luteolysis. These luteotrophic effects may result in appropriate luteal development and function in cows during the estrous cycle and early pregnancy.