Prostacyclin synthesis is stimulated by a serum factor formed during coagulation.

Fresh aortic rings incubated in serum produce more 6-oxo-PGF1 alpha, the stable hydrolysis product of prostacyclin, than in plasma or buffer. A method is described of recovering this stimulatory activity from a dialysate of serum, showing that the activity is due to a prostacyclin stimulating factor. This factor is formed during coagulation initiated by the intrinsic pathway but not by the extrinsic pathway or by thrombin. By contrast with a previously described plasma factor, the activity of the prostacyclinstimulating factor in serum is not greater in serum from patients with renal failure than from healthy controls. The stimulating factor is antagonised by heparin, but differs in other ways from previously described platelet derived stimulating factor(s).