PTGS1 and serum lipopolysaccharide activity: It is important to note that in vascular disease there may be changes in the expression of COX isoforms that alter their relative roles in antithrombotic protection; however, even in severe atherosclerosis, COX1 remains the dominant driver of prostacyclin production by systemic arteries19,20 with a contribution from COX2 only appearing under conditions of endotoxemia.21