An inhibitor of type-1 cyclo-oxygenase in tissues from human pregnancy

Background previous work has shown that first trimester human decidua conta ins a protein which directly inhibits the activity of type-1 cyclo-oxygenas e (COX-I). Methods. Activity assays for cyclo-oxygenase types I and II were developed. Cell cytosol was prepared from a number of different sources: human placen ta and decidua (first and third trimester), two placental cell-lines (BeWo and TCL-1), an endometrial stromal cell-line and K562 erythroleukemia cells . The effects of all cytosols on activity of type I cyclo-oxygenase, and of cytosols from BeWo choriocarcinoma and decidual cells on type II enzyme, w ere tested. Results. Cytosols from first trimester human placenta, two placental cell-l ines, an endometrial stromal cell-line and K562 erythroleukemia cells all i nhibited the type I enzyme, The inhibitor protein could not be detected in third trimester human decidual cells after labor, and was present only at v ery low levels in third trimester decidua prior to the onset of labor. Cyto sols from BeWo and decidual cells had no effect on the activity of the type -2 cyclo-oxygenase enzyme. Conclusions, The inhibitor of type I cyclo-oxygenase was not specific to pr egnancy-related tissues, and may be a general regulator of this enzyme. Low er levels of inhibitor were present at term, but the physiological signific ance of this is unclear. The cytosolic inhibitor appears to be specific to the type I enzyme.