- PROBLEM: Uterine artery was shown to be unique in its capacity to change in size and function during pregnancy. As interleukin-1 (IL-1) was shown to be involved in reproduction processes, the aim of this study was to determine the levels of IL-1 activity of the uterine artery tissue in pregnant rat. METHOD OF STUDY: Nine virgins and nine midpregnant rats were selected. Both uterine arteries were obtained, together with reference tissues from aorta and uterus. The levels of IL-1 were examined in the above tissues after culturing with media alone (control; CT), and media that contained stimulants like tumor necrosis factor-alpha (TNF-α) or lipopolysaccharide (LPS). IL-1-like activity was evaluated by its capacity to promote the culture growth of 1A-5 and cytotoxic T lymphocyte derived (CTLD) cell lines. This activity was expressed as optical density (OD)/mg protein of the examined organ. RESULTS: Uterine artery tissue, of pregnant rats, cultured in medium alone produced significantly higher levels of IL-1 than uterine artery of virgin animals under the same conditions (16.2 S.E. 1.3 versus 0.6 S.E. 0.05 OD/mg protein, respectively; P < 0.02). Stimulation of uterine artery in vitro by LPS and TNF increased their capacity to secrete IL-1. In comparison with uterine artery, aorta produced higher levels of IL-1 in virgin rats compared with pregnant rats (13.6 S.E. 1.2 versus 1.6 S.E. 0.1; P < 0.02). Stimulation of aorta tissues (from both virgin and pregnant rats) with LPS, in vitro, significantly decreased their capacity to secrete IL-1 (P < 0.04). Stimulation of aorta tissues from virgin rats with TNF-α, in vitro, did not change their capacity to secrete IL-1 activity. However, stimulation of aorta tissues from pregnant rats with TNF-α decreased the secretion of bioactive IL-1. The levels of IL-1 produced by uterine tissues from virgin and pregnant rats were similar, and stimulation with either LPS or TNF-α significantly decreased their capacity to secrete IL-1 (P < 0.04). CONCLUSIONS: The high level of IL-1 activity detected during pregnancy in the uterine artery may suggest its unique involvement in the changes occurring throughout pregnancy in those blood vessels.