Function of cyclo-oxygenase-1 and cyclo-oxygenase-2 in the ductus arteriosus from foetal lamb: differential...

Area of Science:

• Perinatal physiology
• Biochemistry
• Developmental biology

Background:

• Prenatal patency of the ductus arteriosus is crucial for fetal circulation and is primarily maintained by prostaglandin E2 (PGE2).
• The relative contributions of cyclo-oxygenase-1 (COX1) and cyclo-oxygenase-2 (COX2) to PGE2 formation in the fetal lamb ductus arteriosus have not been fully elucidated.

Purpose of the Study:

• To investigate the differential roles and expression of COX1 and COX2 in regulating PGE2 production and ductus arteriosus patency in fetal lambs at different gestational stages.
• To assess the impact of physiological and pathophysiological stimuli on COX enzyme activity and ductus arteriosus function.

Main Methods:

• Utilized fluorescence microscopy and immunogold staining to determine the abundance and localization of COX1 and COX2 in fetal lamb ductus arteriosus endothelial and smooth muscle cells.
• Administered endotoxin in utero and in vitro to evaluate its effects on COX enzyme expression and localization.
• Employed COX2-specific inhibitor (L-745,337) and a dual COX inhibitor (indomethacin) to assess ductus arteriosus contractility in isolated tissues at term and prematurely.
• Investigated the effects of oxygen exposure and endotoxin pretreatment on ductus arteriosus responses to COX inhibitors.

Main Results:

• COX1 was found to be more abundant than COX2 in ductus arteriosus cells, particularly before term.
• Endotoxin induced COX2 upregulation in vivo but caused its disappearance in vitro; COX1 levels remained largely unchanged.
• COX2 inhibition (L-745,337) caused significant contraction of the term ductus arteriosus, comparable to indomethacin, but was less effective in premature lambs.
• Premature ductus arteriosus showed enhanced contraction to L-745,337 after in vivo endotoxin exposure and oxygen administration.
• Oxygen-induced contraction in premature lambs was potentiated by L-745,337.

Conclusions:

• COX1 and COX2 enzymes exhibit differential developmental expression in the fetal lamb ductus arteriosus.
• While both COX1 and COX2 contribute to PGE2 formation at term, COX1 is the predominant isoform in the premature ductus.
• COX2 appears to gain functional significance before term, especially under inflammatory (endotoxin) and oxygen-related stimuli, influencing ductus arteriosus patency.