Function of cyclo-oxygenase-1 and cyclo-oxygenase-2 in the ductus arteriosus from foetal lamb: differential development and change by oxygen and endotoxin

1 Prenatal patency of the ductus arteriosus is maintained mainly by prostag landin(PG) E-2. Here we have examined the relative importance of cyclo-oxyg enase-1 (COX1) and cyclo-oxygenase-2 (COX2) for PGE(2) formation in the foe tal lamb ductus (0.65 gestation onwards). 2 Using fluorescence microscopy and immunogold staining, COX1 appeared more abundant than COX2 in endothelial and smooth muscle cells, and this differ ence was greater before-term. Inside muscle cells, COX1 and COX2 immunoreac tivity was located primarily in the perinuclear region. Endotoxin, given to the lamb in utero (similar to 0.1 mug kg(-1)), caused COX2 upregulation, w hile an opposite effect with disappearance of the enzyme followed endotoxin treatment in vitro (100 ng ml(-1)). COX1 immunoreactivity remained virtual ly unchanged with either treatment; however, this isoform as well as any in duced COX2 migrated towards the outer cytoplasm. 3 The COX2 inhibitor L-745,337 (1-10 muM) contracted the isolated ductus at term, the response being almost as high as that to indomethacin (dual COX1 /COX2 inhibitor) over the same dose-range. Conversely, L-745,337 was relati vely less effective in the premature. 4 Pretreatment of the premature in vivo with endotoxin enhanced the contrac tion of the ductus to L-745,337, while in vitro endotoxin had a variable ef fect. 5 The premature ductus exhibited a stronger contraction to L-745,337 follow ing exposure to oxygen. On the other hand, the oxygen contraction, which is modest before-term, was enhanced by L-745,337. 6 We conclude that COX1 and COX2 develop unevenly in the ductus. While both enzymes contribute to PGE2 formation at term, COX1 is the major isoform in the premature. COX2, however, may acquire greater importance before-term f ollowing physiological and pathophysiological stimuli.